s-sS-./S./WH/^S Cjj-c, •/&> 429 ^ °' c °+ NOAA Technical Report NMFS Circular 429 Synopsis of Biological Data on Tunas of the Genus Euthynnus October 1979 FAO Fisheries Synopsis No. 122 NMFS/S 122 SAST — EUTHYNNUS 1,75(01)024 mm\ aap mm KK&K »6S£: mom JhSI .-;-'■•"•.'•' '■•-■•, mm WB& U.S. DEPARTMENT OF COMMERCE National Oceania and Atmnsnhprin AHminictratirVn NOAA Technical Report NMFS Circular 429 ^qKMOSp, V* ^HemcK c! * Synopsis of Biological Data on Tunas of the Genus Euthynnus Howard O. Yoshida October 1979 FAO Fisheries Synopsis No. 122 fc © © ©- r U.S. DEPARTMENT OF COMMERCE Juanita M. Kreps, Secretary National Oceanic and Atmospheric Administration Richard A. Frank, Administrator National Marine Fisheries Service Terry L. Leitzell, Assistant Administrator for Fisheries The National Marine Fisheries Service (NMFS) does not approve, rec- ommend or endorse any proprietary product or proprietary material mentioned in this publication. No reference shall be made to NMFS, or to this publication furnished by NMFS, in any advertising or sales pro- motion which would indicate or imply that NMFS approves, recommends or endorses any proprietary product or proprietary material mentioned herein, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of this NMFS publication. CONTENTS Page Introduction 1 1 Identity 1 1.1 Nomenclature 1 1.11 Valid name 1 1.12 Synonymy 2 1.2 Taxonomy 2 1.21 Affinities 2 1.22 Taxonomic status 4 1.23 Subspecies 6 1.24 Standard common names, vernacular names 6 1.3 Morphology 6 1.31 External morphology 6 *1.32 Cytomorphology 1.33 Protein specificity 8 2 Distribution 8 2.1 Total area 8 2.2 Differential distribution 11 2.21 Spawn, larvae, and juveniles 11 2.22 Adults 13 2.3 Determinants of distribution changes 13 *2.4 Hybridization 3 Bionomics and life history 14 3.1 Reproduction 14 3.11 Sexuality 14 3.12 Maturity 14 3.13 Mating 15 3.14 Fertilization 15 3.15 Gonads 15 3.16 Spawning 15 3.17 Spawn 21 3.2 Preadult phase 22 3.21 Embryonic phase 22 3.22 Larvae and adolescent phases 23 3.3 Adult phase 31 3.31 Longevity 31 3.32 Hardiness 31 3.33 Competitors 31 3.34 Predators 31 3.35 Parasites, diseases, injuries, and abnormalities 31 3.36 Physiology, biochemistry, etc 34 3.4 Nutrition and growth 35 3.41 Feeding 35 3.42 Food 36 3.43 Growth rate 36 3.44 Metabolism 38 3.5 Behavior 38 3.51 Migrations and local movements 39 3.52 Schooling 39 3.53 Responses to stimuli 39 4 Population 41 4.1 Structure 41 4.11 Sex ratio 41 4.12 Age composition 41 4.13 Size composition 41 4.14 Subpopulations 46 hi 4.2 Abundance and density (of population) 47 4.3 Natality and recruitment 47 4.31 Reproduction rates 47 *4.32 Factors affecting reproduction *4.33 Recruitment *4.4 Mortality and morbidity *4.5 Dynamics of population *4.6 The population in the community and the ecosystem ) Exploitation 47 5.1 Fishing equipment 48 5.2 Fishing areas 49 5.3 Fishing seasons 49 5.4 Fishing operations and results 51 *5.41 Effort and intensity 5.42 Selectivity 51 5.43 Catches 51 "6 Protection and management *7 Pond fish culture Literature cited 52 "No information available. IV Synopsis of Biological Data on Tunas of the Genus Euthynnus HOWARD 0. YOSHIDA 1 ABSTRACT Biological and fisheries data on Euthynnus affinis, E. alletteratus, and E. lineatus from published and unpublished sources were compiled, synthesized, and summarized following the FAO species syn- opsis outline. INTRODUCTION The fishes of the genus Euthynnus are widely distri- buted in the warm and tropical waters of the world's oceans. In some localities they appear to be the domi- nant scombrid in the coastal, nearshore waters. Euthyn- nus alletteratus is one of the commonest scombrids in the western North Atlantic (Rivas 1951). In trolling surveys off the southeastern coast of the United States this spe- cies was caught most often (Anderson 2 ). Ben-Tuvia (1957) stated that E. alletteratus seemed to be the only common scombrid along the coast of Israel in the Medi- terranean. In Hawaiian waters E. affinis was one of the more common species taken by trolling (Welsh 1949; Tester and Nakamura 1957). Walford (1937) stated that E. lineatus was very abundant in the eastern tropical Pacific. Although the species of Euthynnus are widely distrib- uted and apparently abundant in some localities, gen- erally the group as a whole is not commercially as impor- tant as the other tunas, e.g., skipjack tuna, Katsuwonus pelamis. Calkins and Klawe (1963) stated that E. lin- eatus was of no commercial value and Kikawa and staff (1963) noted that consumer demand for E. affinis was not very great in Japan. The world landings of Euthynnus ranged from 80,350 to 87,735 metric tons (t) and aver- aged about 84,674 t during the period from 1973 to 1976 (FAO 1977). Because the world demand for tuna is steadily growing and since several of the commercially important tunas are at or near the level of maximum sustainable yield, the underexploited and presently commercially unim- portant tuna and tunalike species are likely to attract more attention. Therefore it is important that the life history and biology of these species, including Euthyn- nus, be elucidated. The purpose of this report is to collate and update all the information presently available on Euthynnus. All 'Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA, Honolulu, HI 96812. Anderson, W. W. 1954. Progress report, South Atlantic Fishery Investigations, Appendix SA-2. In Atlantic States Marine Fisheries Commission, 13th Annu. Meet., Baltimore, Part 2, p. 211-213. papers on Euthynnus published in the FAO Species Synopsis series (Calkins and Klawe 1963; Kikawa and staff 1963; Marchal 1963; Williams 1963) were relied on heavily in preparing this report. 1 IDENTITY 1.1 Nomenclature 1.11 Valid name Collette (1978) discussed the relationships of the groups of fishes in the subfamily Scombrinae, including Euthynnus. He pointed out that some workers (Fraser- Brunner 1950; Collette and Gibbs 1963) placed the monotypic Katsuwonus in synonymy with Euthynnus, which he thought obscured the relationships of Euthyn- nus (sensu stricto) with Auxis and of Katsuwonus with Thunnus. The status of the species within Euthynnus is clear; there are three allopatric species of Euthynnus through- out the world: E. affinis (Cantor) of the Indo-West Pa- cific, including Hawaii and the Red Sea; E. alletteratus (Rafinesque) of the Atlantic Ocean (including the Medi- terranean Sea, the Caribbean Sea, and the Gulf of Mex- ico); and E. lineatus Kishinouye of the eastern Pacific. Euthynnus affinis was originally described as Thynnus affinis Cantor 1850. The holotype was from Penang, most likely from the Strait of Malacca. It was 536 mm (FL) long and is preserved as a dried skin in the British Museum as BMNH 1860.3.19.214 (Collette 3 ). The little tuna from the eastern Pacific was originally described as Euthynnus lineatus Kishinouye 1920 and still retains that name. Euthynnus alletteratus has long been accepted as the valid name of the Atlantic little tuna. It was first de- scribed as Scomber alletteratus Rafinesque 1810. It was claimed recently by Postel (1973), however, that the fish described and figured by Rafinesque is actually Auxis rochei and that the specific name for the Atlantic little tuna should be Euthynnus quadripunctatus of Geoffroy 3 B. B. Collette, Systematics Laboratory, National Marine Fisheries Service, NOAA, Washington, DC 20560, pers. commun. March 1978. Saint Hilaire (1817). However, Tortonese (1975) argued for the retention of the name alletteratus. It was also pointed out that Rafinesque (1810) described Sarda sarda (as Scomber palamitus), Auxis rochei (as S. bisus), and E. alletteratus (as S. alletteratus) and that he could not have confused "bisu" (Auxis) with "alletterata" (Euthynnus) (Tortonese 1976). Thus Scomber quadri- punctatus of Geoffroy Saint Hilaire (1817) is listed here- in as a junior synonym of Euthynnus alletteratus. 1.12 Synonymy The synonymies given below make no distinction be- tween objective and subjective synonyms. The synon- ymies for Euthynnus affinis and E. alletteratus are based on synonymies given by Jones and Silas (1964) and Fraser-Brunner (1949), respectively. There are no syn- onyms for E. lineatus. Euthynnus affinis Thynnus affinis Cantor 1850 (Penang). Thynnus thunnina. Temminck and Schlegel 1850 (Japan). Auxis taso (not of Cuvier) Bleeker 1850 (Java). Euthynnus alletteratus. Jordan, Tanaka, and Snyder 1913 (Japan). Euthynnus yaito Kishinouye 1923 (Japan). Gymnosarda alletteratus. Meek and Hildebrand 1923 (Panama). Wanderer wallisi Whitley 1937 (New South Wales, Australia). Euthynnus affinis affinis. Fraser-Brunner 1949 (Aden, Seychelles, Thailand). Euthynnus affinis yaito. Fraser-Brunner 1949 (Japan, Hawaii, Pacific islands). Euthynnus affinis. Rosa 1950 (in part). Euthynnus alletteratus affinis. de Beaufort 1951 (in part) (Indo-Pacific). Euthynnus wallisi. Whitley 1964 (Australia). Euthynnus alletteratus Scomber alletteratus Rafinesque 1810 (Sicily). Scomber quadripunctatus Geoffroy Saint Hilaire 1817 (Egypt). Thynnus leachianus Risso 1827 (Nice). Thynnus thunnina Cuvier 1829 (Mediterranean). Thynnus brevipinnis Cuvier in Cuvier and Valenciennes 1831 (Mediterranean). Thynnus brasiliensis Cuvier in Cuvier and Valenciennes 1831 (Brazil). Euthynnus alletteratus. Jordan, Evermann, and Clark 1930 (western Atlantic). Euthynnus thunnina. Nobre 1935 (Portugal). Euthynnus alletteratus alletteratus. Fraser-Brunner 1949 (North Atlantic). Euthynnus alletteratus aurolitoralis. Fraser-Brunner 1949 (Gold Coast). 1.2 Taxonomy 1.21 Affinities — Suprageneric Phylum Chordata Subphylum Vertebrata Superclass Gnathostomata Class Osteichthyes Subclass Actinopterygii Order Perciformes Suborder Scombroidei Family Scombridae Subfamily Scombrinae Tribe Thunnini — Generic Genus Euthynnus Jordan and Gilbert 1882. The generic concept of Euthynnus as given below fol- lows that of Godsil (1954a) and Collette (1978). The species of Euthynnus are fusiform, streamlined, and have a lunate caudal fin similar to all tunalike fishes. The body is naked except for the scaly corselet. A series of oblique or longitudinal black markings above the lateral line distinguishes Euthynnus from Katsu- wonus, which has black longitudinal stripes on the belly. The contiguous or nearly contiguous dorsal fins dis- tinguishes Euthynnus from Auxis, which has widely sep- arated dorsal fins. The concave distal margin of the first dorsal fin separates Euthynnus from Sarda, which has a nearly straight first dorsal margin. The species of Euthynnus usually have eight dorsal and seven anal finlets. Palatine teeth are present in all and vomerine teeth in two of the species. The intestine is straight. There are 37-39 vertebrae. Godsil (1954a) gave a de- tailed description of the generic skeletal characters. Unlike Auxis, Euthynnus has a common trunk for the dorsal and ventral branches of the cutaneous artery. However, Euthynnus is more primitive than Katsu- wonus in that the cutaneous artery's ventral branch is short and dendritic (Godsil 1954a) and much less de- veloped than the dorsal branch. Euthynnus also differs from Auxis wherein the dorsal cutaneous artery lies dor- sal to the corresponding vein and not ventral. In Euthyn- nus the aorta is moved ventrally a distance greater than the depth of the centrum owing to the development of the trelliswork, a distance less than in Auxis and more than in Katsuwonus (Collette 1978). ■ — Specific Euthynnus affinis (Cantor) (Fig. 1). The folowing description is based on that given by Godsil (1954a). The dorsal black markings that are superimposed over a blue to indigo background are most accentuated in the Figure 1. — Variations in the markings of three Euthynnus affinis. (From Godsil 1954a, fig. 65.) anterior region and are more oblique in E. affinis than in the other two species. Black or dusky spots are scattered over a relatively wide area on the belly below the pecto- ral. These spots are variable and cannot be regarded as a specific character. The crest or rise of the lateral line above the pectoral fin is minimal. The crest or rise, when present, is always gentle at its anterior slope. In many specimens the lateral line is almost horizontal from the opercular margin over the anterior third of the pectoral fin, from where it slopes gently downward. The caudal keels are not conspicuously developed and are evident externally only by a dorsoventral flattening of the peduncle. The operculum is relatively straight at the posterior margin and a small dark or black elongated spot is gen- erally present at the dorsal extremity of this margin. The posterior outline of the preoperculum is gently and smoothly rounded. A small irregular dark spot or area is present below the posteroventral margin of the eye. The maxillary extends to or slightly beyond the verti- cal through the middle of the eye and, depending on the size of the specimen, 24 to 35 teeth are on each side of the lower jaw. Vomerine teeth are present but palatine teeth, though always present, may not be as prominent. The dorsal fin is contiguous, is about twice the height of the second dorsal fin, and is roughly half the head length; its dorsal outline is strongly concave. The inser- tion of the anal fin is on a vertical through the origin of the first dorsal finlet, or between this and the end of the second dorsal base. There usually are eight dorsal and seven anal finlets. The gill rakers are fully developed on the first arch only and there is invariably a raker at the angle of the arch including a basal process extending both dorsally and ventrally. The raker count (first arch, left side) is 7 (7-9) + 1+24 (22-24) = 32 (29-34) (sic). Gill teeth (pos- terior rakers) are present on all arches and are most de- veloped on the first arch. Euthynnus alletteratus (Rafinesque) (Fig. 2). The following description is based on Godsil (1954a). Euthynnus alletteratus is distinguished from E. affinis and E. lineatus by the absence of vomerine teeth and by the dorsal markings. The pattern of dorsal markings in- cludes broken, longitudinal black or dark bars running irregularly from the corselet towards the caudal region and are more continuous and regular posteriorly. Anteri- orly, short irregularly curved lines, blotches, or spots, re- place the bars. The markings are superimposed over a background of blue which shades dorsally into the deep blue and black of the middorsal line. The blue fades into silver below the lateral line and the entire belly is silvery or dusky; an irregular number of black or dark spots are present be- tween ventral and pectoral fins, and slightly posterior to the pectorals. The ventral projection of the corselet is variable but generally short, extending posterior to the tip of the pec- toral, a distance not exceeding one-fourth (or occasional- ly more) the length of the pectoral fin in most speci- mens. The maxillary extends posteriorly to a vertical drawn through the middle of the eye. The posterior margin of the operculum is relatively straight and the preoperculum smoothly rounded. The teeth are moderate, individually distinct, and number from approximately 25 to 35 on each side of the lower jaw. The palatine teeth are sharp and conspicuous. Figure 2. — Variations in the dorsal markings of Euthynnus allet- teratus. (From Fraser-Brunner 1949, fig. 2.) Euthynnus lineatus Kishinouye (Fig. 3). The following description is also based on Godsil (1954a). This species can in most instances be readily identi- fied by the dorsal markings, which generally consist of a series of three, four, or five broad continuous black stripes running horizontally on the back from the corselet to the caudal fin. The most ventral stripe starts anteri- orly below the lateral line and generally crosses it in its path to the caudal region. Variations in the pattern con- sist mainly of interruptions in the continuity of the Figure .'). — Variations in the dorsal markings of Euthynnus lineatus. Upper figure represents the typical pattern and the lowest figure shows an extreme variant. (From Godsil 1954a, fig. 56.) stripes, or branching of individual stripes including supplementary short irregular markings between. The black dorsal stripes are superimposed over a back- ground of blue that deepens into black dorsally and shades into grey and silver below. The belly is dusky or silvery; an irregular number (usually from two to six) of black spots are present between the pectoral and pelvic fins. Palatine teeth are present in all specimens; vomerine teeth are present although difficult to discern in some specimens. The posterior margin of the operculum is straight and the free margin of the preoperculum is smoothly rounded. The maxillary extends to a vertical drawn through the center of the eye. A key for the separation of the species of Euthynnus, as adapted from Godsil (1954a), is given below. A. Specimens having 37 (36-38) vertebrae, with four lobes or protuberances on each of two vertebrae, predominantly the 31st and 32d. (Invariably has vomerine teeth; usually has about five continuous, hori- zontal black dorsal stripes; 33 to 39 gill rakers and 29 to 31 gill teeth.) E. lineatus B. Specimens having 39 vertebrae. 1. Vomerine teeth present. No indication of lobes on 33d or 34th vertebrae. (Usually has oblique broken dorsal markings; from 29 to 33 gill rakers and 28 or 29 gill teeth.) E. affinis 2. Vomerine teeth absent, although a longitudinal bony ridge can be felt in this area. Incipient lobes or protuber- ances occur on the 32d and 34th verte- brae. (Usually has broken horizontal dorsal markings; from 37 to 40 gill rakers and 31 or 32 gill teeth; width of snout between anterior margin of eyes less than distance of this plane from tip of upper jaw.) E. alletteratus 1.22 Taxonomic status See also section 1.11. Godsil (1954a) made a detailed comparison of the three species of Euthynnus (Table 1). He indicated that while the specific identity of E. affinis, E. alletteratus, and E. lineatus appeared to be well established, most of the differences that distinguish each species were rela- tive. He noted that all the characters that positively sep- arate the species were skeletal and that only the absence of the dentigerous vomerine plate in E. alletteratus could be used for superficial identification. However, it should be pointed out that E. alletteratus (37-40) is separable from E. affinis (29-33) on the basis of gill raker counts. Euthynnus lineatus is clearly separated from E. affinis and E. alletteratus by having 37 (36-38) vertebrae as op- Table 1. — Tabular comparison and evaluation of suggestive differences in three species of Euthynnus. (From Godsil 1954a, table 17.) The terms used under the column, "nature of difference" are subjective and were not precisely defined by Godsil. Character E. lineatus E. alletteratus E. affinis Nature of difference External Dorsal markings Color Belly spots Lateral line Vomerine teeth Maxillary extent Proportions: Head length Insertion 1st dorsal 2d dorsal anal fin ventral fin Ventral inser- tion to vent Width between anterior mar- gin of eye Gill rakers Gill teeth Anal rays Internal Ventral view of viscera 1. Mosaic 2. Right lobe of liver 3. Fat organ Ureter 1. Branches Skeleton Vertebral column Protuberances Continuous, horizontal bars Darker or deeper hued than in alletteratus or affinis Larger than in affinis a. Dip below second dorsal b. Relatively steep rise above pectoral Present To vertical through center of eye 3.13 to 3.62, as in affinis, longer than alletteratus 2.82 to 3.33, more posterior than alletteratus, as in affinis 1.51 to 1.79, includes affinis and alletteratus 1.37 to 1.55, as in affinis, more posterior than in alletteratus 2.76 to 3.25, as in affinis, more posterior than in alletteratus 2.62 to 3.01, includes affinis and overlaps alletteratus Less than distance from tip of upper jaw to plane through anterior margin of eye 7 to 10+1 +24 to 28 Total count 33 to 39 8 to 10 +21 to 23 Total count 29 to 31 11 to 12 Absent Lateral, as in affinis Absent Large, straight, few collecting tubules as in affinis 37 vertebrae 4 large lobes on each, 31st and 32d vertebrae Broken horizontal bars As in affinis Not recorded No dip below second dorsal Gentle rise above pectoral Absent As in lineatus 3.65 to 3.89, shorter than affinis and lineatus 3.37 to 3.55, more anterior than in affinis and lineatus 1.72 to 1.77, as in lineatus, more anterior than in affinis 1.57 to 1.61, more anterior than in affinis and lineatus 3.27 to 3.46, more anterior than in affinis and lineatus 2.57 to 3.12, overlaps lineatus less than affinis Less than distance from tip of upper jaw to plane through anterior margin of eye 10 to 11 +1 +26 to 28 Total count 37 to 40 9 +22 to 23 Total count 31 to 32 11 to 15 Absent Mesial Absent Generally small, erratic, numerous collecting tubules 39 vertebrae Incipient lobes on 33d and 34th vertebrae Broken oblique bars Indicative As in alletteratus Relative Consistently smaller than in Relative lineatus No dip below second dorsal Indicative No pronounced rise above Relative pectoral Present Positive To or beyond vertical through Indicative center of eye 3.44 to 3.60, as in lineatus, Biometrical longer than alletteratus 3.11 to 3.23, as in lineatus, Biometrical more posterior than in alletteratus 1.65 to 1.70, as in lineatus, Biometrical more posterior than in alletteratus 1.48 to 1.52, as in lineatus, Biometrical more posterior than in alletteratus 3.07 to 3.24, as in lineatus, Biometrical more posterior than in alletteratus 2.75 to 2.95, as in lineatus, Biometrical greater than alletteratus Greater than distance from tip Biometrical of upper jaw to plane through anterior margin of eye 7 to 8 + 1 + 22 to 24 Biometrical Total count 29 to 33 8 +20 to 21 Biometrical Total count 28 to 29 13 to 14 Biometrical Present, generally Indicative Lateral, as in lineatus Doubtful Present, generally Indicative Large, straight, few collect- Relative — ing tubules as in lineatus questionable 39 vertebrae Positive No trace Positive posed to 39. It is further differentiated by the presence of four characteristic lobes on each of the 31st and 32d vertebrae and by having the major portion of the caudal bony keel on these two vertebrae. The major portions of the caudal bony keels are on the 33d and 34th vertebrae in E. affinis and E. alletteratus. Euthynnus affinis and E. alletteratus are specifically different in several structural features: the absence of vo- merine teeth in E. alletteratus, the presence of incipient lobes on the 33d and 34th vertebrae in E. alletteratus and their absence in E. affinis. Identification of E. affinis and E. alletteratus could be made by the presence of vomer- ine teeth, together with the broken oblique dorsal mark- ings in E. affinis and the broken horizontal markings in E. alletteratus, and the number of gill rakers. Godsil (1954a) also noted that E. affinis differed slight- ly from E. alletteratus in many of the body proportions. In summing the ratios resulting from dividing the body length (fork length) in each case by the head length, first dorsal insertion, second dorsal insertion, anal insertion, and ventral insertion, he obtained figures ranging from 12.86 to 13.23 for E. affinis (eight specimens 378-643 mm Table 2. — Common and vernacular names of Euthynnus affinis, E. alletteratus, and E. lineatus. Country Standard common name(s) Vernacular name(s) Euthynnu. Australia Mackerel tuna, little tuna Sri Lanka Lesser bonito, mackerel tuna China — Comoro Island Bonito East Africa Bonito, little tuna Hawaii, U.S.A. Little tuna India — Indochina Indonesia — Japan Madagascar Malaysia Mauritius Mirjurtein coast Mogadiscio New Guinea Pakistan (West) Philippines Seychelles Somalia Abidjan Angola France Ghana Guinea Ivory Coast Mauritania Portugal Senegal South Africa Spain Tunisia United States Ecuador Mexico Peru United States Yaito Bonite Bonito Kababida Dwarf bonito Oceanic bonito Little tunny, bonito s affinis Atavalla, Ragodura, Sureya (Sinhalese), Shurai (Tamil) Tow chung Mibassi, Mpassi Sehewa (Kiswahili) — also refers to Auxis spp. and Katsuwonus pelamis Bonito, kawakawa Choori min, suraly (Tamil); ohaman, chuki (Marathi) Ca ngu Tongkol, diverg-bonito, tongkol komo, poetilai Suma, hiragatsuwo, obosogatsuwo segatsuwo, sumagatsuwo, watanabe Thonnine Tongkol; Ikanayer, Sembak, Choreng, Kembel-mas, Tombal-mas (Malay) Bonite Shirwa, shirwi (Arabic) Maba'adi (Somali); Jeidha (Somali), also refers to small Thunnus albacares and Megalaspis cordyla Dawan, Chooki, Jukko Katsarita, turingan, yaito bonito Bonite Euthynnus alletteratus Bonita Thonine Atun Merma El'la (Apollonien), Poponkou (Keta) Makreni Klewe (Kru), bokou-bokou (Alladian) Corrinelo (Vermeulen) Fule-fule Walaz (Ouolof), dolo-dolo (Lebau) Merma Little tunny, little tuna, mackerel tuna Bacoreta Little tunny Euthynnus lineatus Negra, bonito negro Barrilete negro Barrilete negro Black skipjack Cross-bred mackerel R'zem False albacore FL) and 13.64 to 14.19 for E. alletteratus (seven speci- mens 503-763 mm FL). He found that these values were independent of fish size for both species so that mean values, 13.046 for E. affinis and 13.996 for E. alletteratus, could be used to define the species. The head of E. affinis was proportionately larger and the fins were more poste- riorly inserted. 1.23 Subspecies No subspecies are recognized. 1.24 Standard common names, vernacular names The common and vernacular names of the three spe- cies of Euthynnus are given in Table 2. 1.3 Morphology 1.31 External morphology The pattern of markings may vary, sometimes consid- erably, in the three species of Euthynnus (Fraser- Brunner 1949; Godsil 1954a). (See Figs. 1-3.) Euthynnus affinis Godsil (1954b) made morphological studies on E. af- finis from Hawaii and Japan (Table 3). He found several minor differences in the body proportions offish from the two areas but concluded that these differences merely indicated population differences. Meristic data on E. affinis from various areas are given in Table 4. Table 3. — Body proportions of Euthynnus affinis from Japan and Hawaii. (From Godsil 1954b, table 1.) Range in ratios Proportions Head length 1st dorsal insertion 2d dorsal insertion Anal insertion Ventral insertion Greatest body length Dorsal-ventral distance Dorsal-anal distance Ventral insertion to vent Length of 1st dorsal base Length of 2d dorsal base Length of anal base Pectoral length Height of 1st dorsal Height of 2d dorsal Height of anal Diameter of iris 1 Maxillary length 1 Snout to posterior margin of eye 1 Japan Hawaii 3.66-3.72 3.44-3.60 3.07-3.27 3.11-3.23 1.64-1.67 1.65-1.70 1.53-1.54 1.48-1.52 3.33-3.43 3.07-3.24 — 3.55-3.99 3.97-4.18 3.86-4.18 2.31-2.37 2.28-2.38 2.75-2.86 2.75-2.95 3.24-3.41 3.23-3.53 14.07-15.96 14.29-15.53 13.76-14.46 14.02-17.38 6.23-6.88 5.54-6.05 6.86-7.00 6.41-7.00 13.83-14.78 12.10-14.15 13.83-15.00 11.91-14.15 7.27-7.82 6.06-8.00 2.49-2.53 2.31-2.51 2.35-2.38 2.14-2.34 'Ratio of this measurement is to head length. All other measurements are related to fork length. Table 4.— Enumerative data on Euthynnus affinis. First Second dorsal dorsal Dorsal Anal Anal Pectoral Gill Area fin fin finlets fin finlets fin rakers Sri Lanka Deraniyagala (1952) 14-15 12 Munro (1955) 15 20 East Africa Morrow (1954) 14-15 11-12 Williams (1956, 1964) 15-16 11-13 India Jones and Silas (1964) 14 11-14 Indonesia De Beaufort and Chapman (1951) 15 13 Indo-Pacific Fraser-Brunner — — (1949, 1950) Madagascar Fourmanoir (1957) 15 11-13 [Pakistan.] (west) Central Fish 15 13-14 Department (1955) Red Sea Steinitz and Ben- 15-16 — Tu via (1955) Reunion Blanc and Postel — — (1958) South Africa Smith (1961) 15-16 11-13 Japan Godsil (1954b) 15 12-13 Hawaii Godsil (1954b) 14-15 12-13 H-9 14-15 7 28 22-24 (lower arch) 14 7 26 24 (lower arch) 12-14 6-7 13-14 6-7 " (7-10) + (22-23) = 29-33 12-15 6-8 24-28 (7-10) + (22-25) = 29-35 14 7 24 24 (lower arch) — - - (7-10) + (22-23) = 29-33 13-15 7-8 — 25 (lower arch) 14 8 26 12-15 6-8 14 7 13-14 7 23-24 (lower arch) 8+1+24 = 33 25 (lower arch) 8 + 1-H22-24) = 31-33 (7-9) + 1 + (22-24) = 29-34 Euthynnus alletteratus Based on body proportions of E. alletteratus taken along the eastern Atlantic, Marchal (1963) indicated that there were no noteworthy differences in the samples from Cap Vert, Senegal, to Ghana. Postel (1956) compared body proportions and meristic data of E. alletteratus from the Mediterranean Sea (Tunisia) and the eastern Atlantic Ocean (Senegal). He noted that the Tunisian sample was characterized by a shorter head and a shorter predorsal (snout to insertion of first dorsal) and preventral (snout to insertion of ven- tral) distance (Table 5). The Tunisian specimens also had a smaller number of gill rakers (36-41) than the Senegalese specimens (<38-47). Body proportions of E. alletteratus from the U.S. Atlantic coast are given by Godsil (1954a) (Table 6). He also presented meristic data from these fish, which are shown below. Meristic character First dorsal spines Second dorsal rays Counts 10-15 12-13 Dorsal finlets Anal rays Anal finlets Gill rakers 8 11-15 7 (10-11) + (0-1) + (26-28) = 37-40 Mansueti and Mansueti (1962) prepared a "topo- graphic" osteology of a specimen captured in Chesa- peake Bay (Fig. 4). Euthynnus lineatus Body proportions of E. lineatus are given in Table 7. Meristic data, from Godsil (1954a), are given below. Meristic character Counts First dorsal spines 13-15 Second dorsal rays 11-12 Dorsal finlets 8-9 Anal rays 11-13 Anal finlets 7-8 Gill rakers (7-11) +1 + (23-29) = 31-41 Table 5. — Body proportions of Euthynnus alletteratus from Tunisia and Senegal (Postel 1955b: 132-133; 1956: 54). Ratios indicate fork length divided by length of body parts. Length Ratios class Head First dorsal Ventral Pectoral (cm) N length insertion insertion length Tunisia 40-45 1 4.27 3.40 3.40 7.06 45-50 2 4.21 3.57 3.48 6.99 50-55 11 4.22 3.50 3.46 6.99 55-60 30 4.24 3.55 3.50 6.95 60-65 10 4.29 3.56 3.53 6.90 65-70 16 4.28 3.53 3.53 6.70 70-75 13 4.29 3.55 3.53 6.82 75-80 3 4.21 3.59 3.55 6.86 80-85 5 4.29 3.60 3.57 6.88 85-90 5 4.33 3.58 3.55 6.88 90-95 3 4.40 3.67 3.59 6.81 95-100 1 4.37 3.65 Senegal (Males) 3.62 7.06 30-35 1 3.82 3.25 3.15 — 35-40 7 3.84 3.28 3.18 6.12 40-45 81 3.85 3.30 3.20 6.08 45-50 62 3.85 3.30 3.22 6.14 50-55 13 3.87 3.33 3.24 6.31 55-60 ... — — — Table 6. — Body proportions of seven Euthynnus al- letteratus from the western Atlantic (Atlantic coast of United States). Fork length the numerator except those indicated by an asterisk, where head length is the numerator. (From Godsil 1954a, table 15.) Proportions Ratios Head length 3.65-3.89 1st dorsal insertion 3.37-3.55 2d dorsal insertion 1.72-1.77 Anal insertion 1.57-1.61 Ventral insertion 3.27-3.46 Greatest body depth 3.91-4.16 Greatest body width 6.07-6.12 Dorsal-ventral distance 4.08-4.36 Dorsal-anal distance 2.37-2.50 Ventral insertion to vent 2.87-3.12 Length of first dorsal base 3.30-3.57 Length of second dorsal base 14.16-17.25 Length of anal base 13.80-16.05 Pectoral length 5.89-6.50 Height of 1st dorsal 6.90-7.74 Height of 2d dorsal 10.78-13.55 Height of anal 10.78-12.74 Diameter of iris *7.81-8.35 Maxillary length *2.54-2.74 Snout to posterior margin of eye *2. 43-2. 45 1.33 Protein specificity The erythrocytes of two E. lineatus were tested with a series of 540 bean extracts as part of a preliminary work on a program for typing fish blood. On the basis of agglu- tinations, it was determined that the blood of E. lin- eatus can be differentiated from that of six other scorn - brids in the eastern tropical Pacific (Calkins and Klawe 1963). 2 DISTRIBUTION 2.1 Total area In general the species of Euthynnus are coastal fishes found in tropical and subtropical waters of the world. Of the three species, E. lineatus has the most restricted distribution, occurring only in the eastern tropical Pa- cific Ocean. Euthynnus affinis and E. alletteratus are Table 7. — Measurements (millimeters) and proportions of Euthynnus lineatus. Fork length the numerator except those indicated by an asterisk, where head length is the numerator. (From Godsil 1954a, table 10.) Fish number Proportions 19 20 24 26 28 29 30 31 32 33 34 35 36 37 38 Ratios Body length 520 574 583 492 472 446 427 613 514 432 476 455 484 ca 443 462 Head length 150 167 170 157 137 138 123 176 148 116 136 132 137 132 134 3.13- 3.72 1st dorsal insertion 165 186 183 Broken 150 158 133 197 L60 129 146 142 145 145 143 2.82- 3.35 2d dorsal insertion 306 345 340 326 283 293 252 367 299 249 278 267 280 ca 269 272 1.51- 1.79 Anal insertion 33(i 384 386 359 308 315 281 408 339 280 305 295 316 292 302 1.37- 1.56 Ventral insertion 164 182 — 178 154 153 137 198 167 132 153 146 168 147 154 2.76- 3.27 Greatest body depth 132 157 — 148 ca. 123 131 — — 128 — — — — — — 3.32- 4.58 Greatest body width ca. 85 — — — ca. 79 — — — ca.85 — — — — — — 5.93- 6.17 Dorsal-ventral distance 128 147 — — 116 127 — — 120 — — — — — — 3.51- 4.55 Dorsal-anal distance 210 241 — — 192 204 — — 210 — — — — — — 2.19- 2.50 Ventral insertion to vent [80 206 — 187 157 170 144 205 175 147 149 153 153 143 150 2.62- 3.19 Length 1st dorsal base 146 168 — Broken 137 143 — — 145 — — — — — — 3.12- 3.86 Length 2d dorsal base 32 33 — — 30 34 — — 31 — — — — — — 13.12-18.84 Length of anal base 31 31 — — 24 30 — — 31 — — — — — — 14.87-20.10 Pectoral length 84 88 — 89 78 84 — — 87 — — — — — — 5.31- 6.99 Height of 1st dorsal 66 72 — Broken 64 71 — — 76 — — — — — — 6.28- 7.97 Height of 2d dorsal 33 Broken — — 33 35 — — 36 — — — — — — 12.74-16.63 Height of anal 34 ca. 45 — — 36 35 — — 35 — — — — — — 12.74-18.29 Diameter of iris 23 ca.20 — 20 — 20 — — 19.5 — — — — — — *6.00- 7.85 Maxillary length 59 65 — 57 53 52 — — 57 — — — — — — •2.48- 2.75 Snout to posterior margin of eye — — — — ca.58 — — — 62 — — — — - — * 1.97- 2.39 83 3 § a a -n Oj -o 3 c C ta cs 13 ~ X s rt s- £ u. 3 C X i- — I 3 more widely distributed in the world's oceans. The geo- graphic classification and codes from Rosa (1965) were used in part to describe the distribution of the species. Euthynnus af finis ISEW (Indo-Pacific, central) ISW (Indian Ocean) 100 Africa. 120 northeastern area; 130 eastern central area; 156 Malagasy Republic. 400 Asia. 420 central area; 430 southeastern area; 440 eastern area (mainland); 450 eastern area (is.). 600 Oceania. 610 Australia; 640 eastern Oceania; 660 U.S.A. (Hawaii); 670 Pacific Is.; 680 central groups. Euthynnus affinis is widely distributed in the warm waters of the Indo-Pacific region (Fig. 5). In the western Pacific it is found from the coast of southern Japan, throughout the Ryukyu Islands, Taiwan, along the coast of Indochina, the Philippines, and around Borneo and New Guinea (Kikawa and staff 1963). Whitley (1964) re- ported its occurrence (as Euthynnus wallisi) along the west, north, and east coasts of Australia. It also occurs around oceanic islands of the Pacific including the east and west Carolines and the Marshall Islands (Kikawa and staff 1963), the Gilbert Islands (Randall 1955), the Hawaiian Islands, Midway (Chapman 1946), the Line Islands and the Marquesas Islands, New Caledonia and New Hebrides (Angot 1959), and Tahiti (Herre 1932). A stray E. affinis was recorded from Los Angeles Harbor, Calif. (Fitch 1953). No exhaustive search of the lit- erature was made for records of E. affinis in the Pacific Ocean. However, the records listed herein suggest that E. affinis may have a wider distribution than indicated here and in Figure 5. In the Indian Ocean the distribution of E. affinis is es- sentially continuous along the entire east African coast including the Red Sea and the Gulf of Aden, along the coast of Pakistan and both coasts of India, Burma, Malaysia, and Indonesia, and to the west coast of Australia. It occurs around Madagascar (Malagasy Re- public), Sri Lanka (Ceylon), and the offshore islands and archipelagos of Mauritius, Reunion, Comoro, the Sey- chelles including Aldabra, Laccadive, Maldives, and Andaman and Nicobar (Williams 1963; Jones and Silas 1964). Euthynnus alletteratus ANW (Atlantic, NW) ASW (Atlantic, SW) ANE (Atlantic, NE) ASE (Atlantic, SE) 100 Africa. 110 northwestern area; 140 western central area; 150 southern area. 200 North America. 236 New Englad; 237 Middle Atlantic States; 235 southern states; 238 southern Atlan- tic states. 300 Latin America. 311 Mexico; 320 Caribbean Is.; 351 Brazil; 352 Uruguay; 353 Argentina. 500 Europe. 510 Scandinavia; 520 western area (mainland); 530 British Isles; 540 southern area; 550 southeastern area. Euthynnus alletteratus is found along both coasts of the Atlantic Ocean and in the Mediterranean Sea. It is also found in the Sea of Marmara and it occurs spo- radically in the Black Sea (Demir 1961, 1963) (Fig. 6). In the eastern Atlantic Ocean, Laevastu and Rosa (1963), in their distributional chart of E. alletteratus, indicate that the limits of the "regular" distribution of this species are from off the coast of Morocco to the coast of northwest Africa. Marchal (1963) listed the following areas along the west African coast from which E. allet- teratus has been recorded: Levrier Bay, Mauritania (Postel 1950); Cape Verde Islands and Gambia (Cadenat 1950; Postel 1950); off the Bissagos, Guinea, and Sierra Leone (Marchal 1961; Postel 1962); the length of the Figure 5.— Distribution of Euthynnus affinis in the Indo-Pacific region. (Adapted from Kikawa and staff 1963, fig. 2, and Laevastu and Rosa 1963, fig. 4.) 10 Figure 6. -Distribution of Euthynnus alletteratus. Laevastu and Rosa 1963, fig. 4.) (Adapted from coast of Liberia, the Ivory Coast and Ghana; St. Thomas and Principe Islands (da Costa and Frade 1958); and Pointe-Noire (Roux 1957). The distributional chart of E. alletteratus in the west- ern Atlantic given by Laevastu and Rosa (1963) shows the limits of its distribution from the coast of Maine to the northern boundary of Brazil. Briggs (1958) stated that in the western Atlantic E. alletteratus is distrib- uted from "Bermuda and the Gulf of Maine to Ilha Vic- toria, Brazil, and the northern and eastern Gulf of Mex- ico." Fraser-Brunner (1949) also recorded the species from Rio de Janeiro, Brazil. Euthynnus lineatus ISE (Pacific, SE) 200 North America. 232 southwestern states (Cali- fornia). 300 Latin America. 310 Central America (mainland); 340 western South America. Euthynnus lineatus is found in the tropical coastal waters of the eastern Pacific from about lat. 35°N to 12°S (Fig. 7). Calkins and Klawe (1963) constructed this fig- ure from records of E. lineatus reported in the literature, tuna vessel logbooks, scientific logs of oceanographic cruises by ships of the Scripps Institution of Oceanog- raphy and the National Marine Fisheries Service, and field-book notes of C. L. Hubbs, Scripps Institution of Oceanography, and D. P. de Sylva, University of Miami. Records of E. lineatus in the literature include the north- ernmost record from off San Simeon, Calif, (lat. 35°20'N, long. 120°40'W) (Nowell 1961), specimens from Cali- fornia waters (Roedel 1948; Fitch 1952), Baja California (Godsil 1954a), the Tres Marias Islands (Fowler 1944), Acapulco, Mexico (Mais and Jow 1960), Costa Rica (Schaefer and Marr 1948), Colombia Bank (lat. 2°N, long. 79°W), Guayaquil Bank (lat. 3°35'S, long. 80° 55'W) (Godsil 1954a; Clemens 1957), and from the Gala- pagos Islands (Fowler 1938, 1944; Schmitt and Schultz 1940; Seale 1940; Godsil 1954a). Logbooks of commercial tuna vessels indicate that E. lineatus has been en- countered nearly everywhere along the coastline from about halfway down the coast of Baja California to northern Peru. They have been frequently encountered in the Gulf of California, the Revillagigedo Islands, all along the coast of Mexico and Central America, and the Galapagos Islands. There have been occasional reports of this species from Clipperton and Cocos Islands and there is a single report of its occurrence from Shimada Bank (lat. 16°52'N, long. 117°30'W) (Calkins and Klawe 1963). More recently, they have been recorded as far as 2,000 mi (3,200 km) off the coast in the eastern Pacific (Klawe 4 ). In addition there are two records of E. lineatus from the Hawaiian Islands (Matsumoto and Kang 1967; Matsu- motol976). 2.2 Differential distribution From all indications it appears that the distribution of all the different life stages of E. affinis and the other two species of Euthynnus appears to be similar. As noted earlier the adults are generally coastal fishes and judging from the distribution of the various life stages of these species, the entire life cycle is completed within the coastal province. 2.21 Spawn, larvae, and juveniles Euthynnus affinis Larval and juvenile E. affinis are widely distributed in the Indo-Pacific area (Fig. 8). As many investigators have observed in the past, e.g., Matusmoto (1959), it ap- pears that larval and juvenile E. affinis are generally taken close to iand masses and less frequently around oceanic islands. There also are a few captures of larval fishes in midocean localities but chances are these were carried away from coastal areas by the prevailing cur- rents. In the coastal waters of southern Japan Yabe et al. (1953) indicate that preadults ranging in length from 150 to 250 mm are taken from August to October near Aburatsu, Kyushu. Preadults also constitute a regular part of the commercial catch in other areas. In the fish- ery for E. affinis off the southwest coast of Sri Lanka, fish smaller than 240 mm appear regularly in the commercial landings (Sivasubramaniani 1970). In the Philippines Wade (1950a) obtained many of his juvenile and pre- adult E. affinis from various fish markets. 4 W. L. Klawe, Inter-American Tropical Tuna Commission, Scripps Institution of Oceanography, La Jolla, CA 92037, pers. commun. to Tamio Otsu, National Marine Fisheries Service, Southwest Fisheries Center, Honolulu, HI 96812, November 1977. 11 ry T 1 1 35° "^ A — ] 120 r~i i ■ ' II5 C "W t- 05 1 3 1 ■ ' 100 I 1 i V 95° i -1 ' 90° -4 85" T 1 _4 iii 80° i ■ i 75° T 1 ■ \ • S | 35° 30° i »"""] STATES \ li r ,J a -»no 25° ^^"N. 1*M? i«. CALIFORNIA < iV * ™ • • l 25° 20° • HS^ *4 !• £ 9 \ 9 i« • • -VwfS MARIAS • • v /Ji. 4*0 J * I 1 .. 1 5° «-H I • « •j t 15' ' » « • , II LJ ■*•> SHIMADA ^ 1 • 1 1" ITT a • t • * •» 10° • f **w sj » * C • * • • ♦ • ® icUPPERTON IS. ^ $ • 05° * • • • i 4 L/« « « • Icoiros * • • 05° 0° ■ f "fl ■T PARAMOUNT ^C • • 7 r~ • 1 1 * _R4i 4,P4<5£>5 "'^^ 1 t 0°- 05° "1 /5Z ;«. 20° - ■ I T-* 1 i i 1 _ i 1 10 i i 1C I— 00 9 y r ■ 1 90 i -r 4- 1 Figure 7. — Distribution of Euthynnus lineatus in the eastern Pacific Ocean. (From Calkins and Klawe 1963, fig. 2.) Euthynnus alletteratus The distribution of larval and juvenile E. alletteratus is shown in Figure 8. They have been recorded from both sides of the Atlantic Ocean, the Mediterranean Sea in- cluding the Black Sea and Sea of Marmara, and from the Gulf of Mexico. In the eastern Atlantic along the west African coast, the northernmost record of larval E. allet- teratus is from off the northern coast of Morocco. There are numerous records of larval E. alletteratus from the Gulf of Guinea. The absence of records from farther south along the coast of Africa may merely reflect lack of sampling effort. In the western Atlantic, larval E. allet- teratus has been collected as far north as lat. 35°42'N off the North Carolina coast of the United States and as far south as lat. 10°S off the coast of Brazil. Although most of the larvae have been collected relatively close to shore, there are a few midocean records of E. alletteratus lar- vae. Richards and Simmons (1971) suggested some sort of vertical stratification in the distribution of larval E. al- letteratus. They noted that the larvae were collected more often at the surface at night. They also tentatively concluded that there was greater net avoidance by larval E. alletteratus during the day. However, they attributed the higher frequency of capture at night to vertical mi- gration. Marchal (1963) stated that along the coasts of the Ivory Coast and Ghana postlarval and juvenile E. allet- teratus were found at the surface from 2 mi (3.2 km) to around 100 mi (160 km) off the coast. Marchal made the observation that those postlarval and juvenile fish found out to 100 mi (160 km) offshore were probably taken out by the currents because no adults were found beyond the 12 Figure 8. — Distribution of larval and juvenile Euthynnus spp. (See Tables 9-11.) continental shelf. He stated that these young forms of all sizes were taken from October to July and that they may be present all year. Marchal observed that preadult E. alletteratus appeared to be closer to the coast than the adults. He indicated that the beach seines did not catch fish over 40 cm long. In the Mediterranean Sea in Haifa Bay, Oren et al. (1959) captured preadults 80 to 240 mm long from the end of June to the middle of August. Also in the Medi- terranean area, Demir (1963) reported the catch of pre- adult E. alletteratus ranging from 145 to 220 mm long in the Sea of Marmara during the period from the last week of August to the second half of September. He also re- ported 180 to 250 mm long preadults in the Dardanelles from the middle of August to the end of the first week in October. In the Gulf of Mexico juvenile and preadult E. allet- teratus 15 to 172 mm long have been commonly found be- yond the edge of the continental shelf throughout the summer months (Bullis 1955). Euthynnus lineatus Larval and postlarval E. lineatus are almost as widely distributed as the adults in the eastern tropical Pacific Ocean (Fig. 8). They have been recorded as far north as lat. 29°45'N (Point Antonio, Baja California) and south to lat. 04°00'N, long. 81°35'W (the vicinity of Malpelo Island) (Calkins and Klawe 1963). The larvae were also collected near the head and entrance of the Gulf of Cali- fornia. Except for one specimen caught near Malpelo Island, all the larval and juvenile E. lineatus have been collected within about 150 mi (240 km) of the mainland. 2.22 Adults See section 5.3. 2.3 Determinants of distribution changes The three species of Euthynnus seldom occur more than a few hundred miles from land. They are usually found around land masses and island chains generally between lat. 35°N and 35°S (Blackburn 1965). Godsil (1954a) noted that E. lineatus along the west coasts of Baja California and Central America appeared to be lo- calized in distribution and confined to certain inshore areas. He also noted that E. af finis in the Hawaiian Islands were confined within the 20 or 30 fathom (36.5 or 54.8 m) contour. In the western Pacific near New Guinea E. affinis were abundant and distributed in inshore waters throughout the area (Mori et al. 1969). Around the Maldive Islands in the Indian Ocean E. affinis are found close to the islands and they often venture into 13 shallow water in pursuit of bait (Jonklaas 1967). In this respect the species of Euthynnus generally appear to be similar to some species of Sarda which are also inhabi- tants of the coastal or neritic, pelagic province. Sver- drup et al. (1942) characterized the neritic province as one where the environment is more variable than in the oceanic. In the neritic province the chemical constitu- ents of the seawater are more variable: salinities are usually lower and some of the inhabitants may be more or less euryhaline. The species of Euthynnus, particularly E. affinis, are also found in waters around oceanic islands and archi- pelagos although here too they are found close to shore. The following example illustrates the type of habitat oc- cupied by the species of Euthynnus. Off the coast of Japan E. affinis may occur in waters with salinities ranging from 31.22 to 33. 80%° (Yabe et al. 1953). Yabe et al. (1953) also noted that near Aburatsu, Japan, heavy autumnal rains make the water turbid 1 or 2 mi (1.6 or 3.2 km) from shore and cause a considerable lowering of the salinity in the surface water. However, these conditions did not seem to affect the catches of E. affinis. Kishinouye (1923) noted that E. affinis in Japanese coastal waters are found in waters ranging from 18°to28°C. Williamson (1970) described the coastal environment of E. affinis around Hong Kong. The coast is composed of steep, rocky headlands and islands and the 50 m contour lies about 25 mi (40 km) offshore. The surface water temperature ranges from 14° to 29°C annually. The west side of Hong Kong is greatly influenced by the estuary waters fed by the West River. The bottom in this area is muddy and the water turbid and brackish (surface salinity, 33°L in February and 6%o in July). On the east side of Hong Kong more oceanic conditions prevail: the surface salinity is 34%o in February and 26%, around Ju- ly, which is the height of the summer rainy season. In the Indian Ocean the tropical and subtropical waters are generally characterized by a scarcity of plankton offshore except in areas where vertical mixing of water masses occurs, e.g., off Somalia, where up- welling takes place. Strong development of phyto- plankton and the ensuing zooplankton is confined to the immediate coastal areas (Williams 1963). Along the Atlantic coast of the United States most of the E. alletteratus are taken in "green water" and are seldom taken in the "blue water," or slope water of the Florida Current (de Sylva and Rathjen 1961). As de Sylva and Rathjen pointed out, E. alletteratus typically occupy the inshore turbid waters. Morice and Cadenat (1952) made a similar observation in Guadeloupe, and Whiteleather and Brown (1945) noted that this species appeared to be a coastal fish in areas around Trinidad, Tobago, and Guyana. Calkins and Klawe (1963) characterized the general habitats of E. lineatus based on published studies (Holmes et al. 1957; Brandhorst 1958; Cromwell 1958; Cromwell and Bennett 1959; Sund and Renner 1959). Calkins and Klawe (1963) noted that E. lineatus occurs in the equatorial Pacific water mass which extends approximately from lat. 23° or 24°N to northern Peru and the Galapagos Islands. There are transition zones to the north and south of the tropical water mass which are influenced by the cold California Current and the Peru Current in the north and south, respectively. The princi- pal warm currents influencing the tropical water mass are the North Equatorial, the Equatorial Counter- current, and the South Equatorial Current. Where E. lin- eatus is most frequently found near the coast, these cur- rents are usually weak and variable and the thermocline is relatively shallow (10-50 m) which allows the exchange of nutrients between the deep layer and the surface waters. In a thermal dome located off Central America (lat. 9°N, long. 90°W) the thermocline is frequently less than 10 m and sometimes reaches the surface. In the Gulf of Panama, the Gulf of Tehuantepec, the Gulf of Cali- fornia, and the inshore waters of Baja California, upwell- ing enriches the inshore waters. 3 BIONOMICS AND LIFE HISTORY 3.1 Reproduction 3.11 Sexuality All of the species of Euthynnus are heterosexual, males and females do not differ in external appearance, and there is no record in the literature of hermaphroditism in these fishes. However, it would not be surprising if hermaphroditic specimens were to occur since cases have been discovered in closely related species, e.g., Katsu- wonus pelamis (Uchida 1961). 3.12 Maturity Euthynnus affinis Euthynnus affinis apparently attains sexual maturity at a relatively small size, at least in certain areas of its distributional range. Buriag (1958) examined a total of 30 E. affinis 44.4 to 62.2 cm long in Philippine waters and found that the smallest female with mature gonads was a specimen 49 cm long. A 47.7 cm female was found to have spent ovaries. In an earlier study in Philippine waters, a sample of 205 females included a ripe specimen between 40 and 40.9 cm long that was determined to be spent. In yet another study comprising a sample of 144 fish 33.4 to 50.8 cm long, it was found that the smallest mature fe- male was around 38.5 cm long (Ronquillo 1963). Euthynnus affinis in the Indian Ocean appears to reach sexual maturity later than those occurring in the Philippines. Based on a sample of 75 specimens taken near the Seychelles, Ommanney (1953) reported that E. affinis attained sexual maturity between 50 and 65 cm TL (total length), probably in the third year of life. Wil- liams (1956, 1963) examined 37 specimens from east Africa and noted that fish there attained sexual maturity between 55 and 60 cm TL. In Mauritius waters E. affinis 14 55 cm long are mature (Baissac 5 ). Off the southwest coast of India near Vizhingam (lat. 08°22'N, long. 76°59'E) the smallest female with ripe ovaries was found to be 48 cm (Rao 1964). In the South China Sea off Kwangtung, China, E. af- finis presumably attains sexual maturity at around 50 cm (Williamson 1970). Elsewhere in this paper William- son also noted that two distinct size-groups of fish made up the spawning schools and that the smaller of the size groups was made up of fish with a mean size of 44 cm which were probably a year old. Around Hawaii, Tester and Nakamura (1957) determined the sex and maturity of 93 E. affinis caught by trolling. However, they did not relate the sexual maturity of the fish to its size. They found that five females in their sample were ripe. chasing by three ripe male E. lineatus in a manner sim- ilar to that described by Magnuson and Prescott (1966) as reproductive behavior of Pacific bonito, Sarda chili- ensis. These observations were made by Hunter and Mit- chell (1967) near drifting objects under which E. lin- eatus had collected off the coast of Costa Rica. Whether these observations actually represented reproductive be- havior by E. lineatus remains to be demonstrated. 3.14 Fertilization Fertilization is external in all the species of Euthyn- nus. 3.15 Gonads Euthynnus alletteratus In the eastern Atlantic in the area off Dakar, Senegal, Postel (1955b) determined the size of first maturity of E. alletteratus as 39.7 cm for the males and 38.6 cm for the females. Postel considered that E. alletteratus were sex- ually mature when the gonadosomatic index reached 3 to 4%, which was related to the time when the sexual products could be expressed by a slight pressure on the body walls. Marchal (1963) stated the smallest E. allet- teratus he observed in spawning condition were 44.2 to 44.7 cm long off the coast of Guinea. In the western Atlantic Ocean off the coast of Florida, de Sylva and Rathjen (1961) observed that the smallest fish in ripe condition was a female 27.2 cm long. How- ever, they also noted that most fish in their sample were not in spawning condition until they were 35 cm long. And in the Spanish fishery for E. alletteratus based at the southern ports of Barbate and Tarifa, it was found that the size at first spawning was 56.5 cm for the males and 57.0 cm for the females (Rodnguez-Roda 1966). Euthynnus lineatus The size at first spawning for E. lineatus is not known. There are only fragmentary observations on the gonadal development of this species in the eastern tropical Pacif- ic where it occurs. Mead (1951) reported two females 54.4 and 55.0 cm long, which had swollen and turgid ovaries, from the waters off Central America. Schaefer and Marr (1948) reported two adults from the Gulf of Nicoya, Costa Rica, in an advanced stage of maturity but did not give their size. 3.13 Mating Although the reproductive behavior of Euthynnus has not been positively observed in the natural environment or in experimental tanks and ponds, Hunter and Mit- chell (1967) observed a high frequency of wobbling and Euthynnus affinis Information on the fecundity of E. affinis is available only from the Indian Ocean. Rao (1964) indicated that E. affinis around Vizhingam spawned 210,000 to 680,000 ova per spawning and 790,000 to 2,500,000 ova during the spawning season (Table 8). He noted that the number of ova produced by E. affinis increased with the size of the fish. Table 8. — Fecundity of Euthynnus affinis in the Indian Ocean off Vizhingam, India. (From Rao 1964, table I.) Fork Weight No. of ova No. of ova length of fish per spawning per spawning season (cm) (kg) (millions) (millions) 48.0 1.37 0.21 0.79 52.5 2.06 0.31 0.88 55.5 2.35 0.30 1.31 58.2 3.20 0.50 2.14 65.0 4.57 0.68 2.50 Baissac, J. de B. 1960. Indian Ocean section - genus Euthyn- nus. Mimeogr. rep., 2 p. CCTA/CSA, Colloque sur les Thonides, Dakar, 12-17 Decembre 1960, Tunny (60) 5. Euthynnus alletteratus Not much information is available on the fecundity of E. alletteratus. Postel (1955b) determined that the fecundity of a 75 cm fish from off the coast of Dakar, Senegal, was 1,750,000 eggs. Euthynnus lineatus The fecundity of E. lineatus has yet to be investi- gated. 3.16 Spawning Euthynnus affinis Euthynnus affinis in the Philippines apparently spawn all year round as indicated by the presence of fish in all stages of sexual development throughout the year (Wade 1950b; Buhag 1958). Wade (1950b) stated that his sam- ple was not sufficiently large to discern possible seasonal variations in spawning intensity. Ronquillo (1963) de- termined the gonad index for a sample of 144 E. affinis in 15 (9) (MO) NUMBER OF FISH ( ) MEAN VALUE RANGE (10) (9) 1 (16) (6) (27) (I) o (9) (28) (3) D J L MAR APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC. Figure 9. — Seasonal distribution of Euthynnus affinis gonad index in the Philippines. (From Ronquillo 1963, table 16.) Gonad index W 3 = rrj X 10 , where W„ is the weight of the paired ovaries in grams and L is fork length in millimeters. Philippine waters to define the spawning season (Fig. 9). His results were essentially the same as those obtained by Wade (1950b) and Buhag (1958) in that no clear seasonality in spawning was evident. Ronquillo (1963), however, noted that the highest gonad indices were found from March to May. Based on the development of ovarian ova, Buhag (1958) concluded that E. affinis in the Philippines spawns more than one batch of eggs dur- ing a spawning season (Fig. 10). Although he did not en- counter any fully ripe ovaries in his samples, Buhag (1958) speculated that ripe eggs of E. affinis would prob- ably be between 0.8775 and 1.1050 mm in diameter. On the basis of the distribution of larval E. affinis in Philippine waters, Wade (1951) indicated that spawning may have seasonal peaks. Matsumoto (1959), however, indicated that Wade may have misidentified the larvae and that what Wade identified as E. affinis were more likely Auxis. Based on an earlier study reporting the cap- ture of juveniles, Wade (1950a) stated that E. affinis spawn in the vicinity of Manado, Celebes, East Indies; near Marigabato Point, Cotabato Province, Mindanao; and Batangas and Balayan Bays, Luzon, Philippines. In the western Indian Ocean near the Seychelles, the spawning season for E. affinis is during the period of the northwest monsoon, from October-November to April- May including a peak from January to March (Omman- ney 1953). Off the coast of east Africa the spawning season extends from January to July, the middle of the northwest monsoon to the beginning of the southeast monsoon (Williams 1963). The capture of larval E. affinis in the western Indian Ocean during the months of De- cember and January (Jones and Kumaran 1964) corrobo- 6 8 10 12 14 16 18 20 22 24 26 28 30 DIAMETER IN MICROMETErt UNITS Figure 10. — Ova diameter frequency polygons of Euthynnus affinis showing the various stages of development of the ova to maturity: I, immature; II, early maturing; III, late maturing; IV, V, V-A, mature; VI, ripe; VII, spent. (From Buiiag 1958, fig. 3.) rates the above observations. In other close-by areas in the western Indian Ocean, fish in spawning condition were taken in November and December around Mada- gascar (Fourmanoir 1957) and in December around Mauritius (Baissac see footnote 5). Off the southwest coast of India near Vizhangam, Rao (1964) indicated that E. affinis spawns from April to September. He did not discount spawning also in other months of the year and noted the possibility that indi- vidual fish may mature and spawn several batches of ova during the spawning season. The capture of juveniles up to 200 mm in the months of January, May, June, September, October, and November near Vizhingam and Calicut, India (Jones 1960; Table 9) suggests a rather lengthy spawning season for E. affinis in these waters. In the eastern equatorial Indian Ocean, larval E. af- finis have been captured from August to October in Indo- nesian waters (Matsumoto 1959; see Table 8) which sug- gested spawning during these months. Larval and juvenile E. affinis have been recorded from many other areas in the Indo-Pacific (Table 9; see also 16 Table 9.— Records of larval and juvenile Euthynnus affinis in the Indo-Pacific. Locality Marine area code [see Number Date Lat. Long. Rosa (1965)] Larvae Juveniles Apr. 1929 04°03'N 123°26'E ISEW 1 04°03'N 123°26'E 3 06°55'N 114°02'E ISEW 15 06°55'N 114°02'E 23 06°55'N 114°02'E 25 08°02'N 109°36.5'E ISEW 1 08°02'N 109°36.5'E 2 — 08°02'N 109°36.5'E 42 May 1929 12°15'N 109°26'E ISEW 1 — 20°30.5'N 125°28'E ISEW 2 — 20°30.5'N 125°28'E 2 — June 1929 14°37'N 119°52'E ISEW 1 July 1929 00°41.5'S 134°14.5'E ISEW 1 — 00°41.5'S 134°14.5'E 3 00°41.5'S 134°14.5'E 2 00°40.5'S 134°15'E ISEW 7 00°40.5'S 134°15'E 3 00°40.5'S 134°15'E 10(?) 00°40.5'S 134°15'E 4 00°40.5'S 134°15'E 4 00°33'S 134°00'E ISEW 11 00°33'S 134°00'E 3 00°33'S 134°00'E 1(7) 01°01'S 137°20'E ISEW 2 01°01'S 137°20'E 3 01°20'S 138°42'E ISEW 1 01°20'S 138°42'E 1 Aug. 1929 07°53'S 116°18'E ISEW 1 07°53'S 116°18'E 2(?) 09°09'S 114°47'E ISEW 2 Sept. 1929 06°22'S 105°12'E ISEW 7(?) 06°22'S 105°12'E 13(?) 04°38'S 99°24'E ISW 1 02°00'S 98°59'E ISW 1 02°00'S 98°59'E 1 — 02°00'S 98°59'E 2 02°07'S 99°53'E ISW 1 01°29'S 100°07'E ISW 2 01°29'S 100°07'E 10 00°52'S 99°25'E ISW 1 — 00°52'S 99°25'E 11 00°52'S 99°25'E 7 — Oct. 1929 02°57'S 99°36'E ISW 1 03°12'S 99°26'E ISW 1 Dec. 1929 01°45'N 71°05'E ISW 1 00°35'N 66°09'E ISW 1 03°45'S 56°33'E ISW 2 — 05°01'S 54°46'E ISW 1 — 08°27'S 50°54'E ISW 1 11°55'S 49°55'E ISW 2 12°09'S 49°34'E ISW 8 — 09°10'S 45°17'E ISW 1 08°24'S 42°54'E ISW 3 — 07°24'S 41°51'E ISW 56 04°45'S 40°10'E ISW 15 Jan. 1930 03°26'S 42°58'E ISW 34 — 04°21'S 42°56'E ISW 2 — 14°16'S 41°48'E ISW 3 16°12'S 42°04'E ISW 14 — 18°30'S 42°18'E ISW 1 21°13'S 42°26'E ISW 3 23°11'S 42°54'E ISW 2 25°14'S 36°21'E ISW 29 Mar. 1948 Manado, Celebes, Netherlands, East ISEW 1 Indies Length (mm) Reference Remarks — Matsumoto(1959) — Matsumoto (1959) — Matsumoto(1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto ( 1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) — Matsumoto (1959) 7.08 Jones and Kumaran 1963) — Jones and Kumaran 1963) 6.05,7.14 Jones and Kumaran 1963) 5.94 Jones and Kumaran 1963) 5.59 Jones and Kumaran 1963) 4.7 Jones and Kumaran 1963) 6.62-12.72 Jones and Kumaran 1963) 6.58 Jones and Kumaran 1963) 5.14-7.94 Jones and Kumaran 1963) 4.68-8.75 Jones and Kumaran 1963) 5.42-12.16 Jones and Kumaran 1963) 4.74-8.69 Jones and Kumaran 1963) 6.11 Jones and Kumaran 1963) 6.79 Jones and Kumaran 1963) 4.79-9.14 Jones and Kumaran 1963) — Jones and Kumaran 1963) 5.69-5.88 Jones and Kumaran 1963) 7.08-8.39 Jones and Kumaran 1963) 4.62-7.42 Jones and Kumaran 1963) 115 Wade (1950a) Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Length not defined Fork length 17 Table 9.— Continued. Locality Marine area code [see Number Length (mm) Reference Date Lat. Ixmg. Rosa (1965)] Larvae Juveniles Remarks Apr. 1948 Batangas, Luzon, Philippines May 1948 7°02'N 124°12'E Taal, Batangas Province, Luzon, Philippines Batangas, Luzon, Philippines Mar. 1949 Batangas, Luzon, Philippines Batangas, Luzon, Philippines Apr. 1949 Batangas, Luzon, Philippines Batangas, Luzon, Philippines Batangas, Luzon, Philippines Aug. -Oct. Off southern Kyushu, 1950 Japan Sept. 1956 Calicut, India Oct. 1956 Vizhingam, India Nov. 1956 Vizhingam, India Jan. 1957 Vizhingam, India May 1958 Vizhingam, India June 1958 Vizhingam, India Aug. 1956 Jan. 1957 Feb. 1957 Mar. 1957 June 1957 Dec. 1957 Oct. 1960 July-Aug. 1960-61 00°01'S 12°31'S 07°55'S 02°58'S 14°57'S 08°12'S 21°11'N 21°25'N 21°24.5'N 09°34'S 133°02'W 132°04'W 110°02'W 129°55'W 146°20'W 145°12'W 158°17.5'W 157°21'W 159°00'W 139°50'W 12°29'N 43°03'E Gulf of Tonkin ISEW ISEW ISEW ISEW ISEW ISW ISW ISEW ISEW ISEW ISEW ISEW ISEW ISEW ISEW ISEW ISEW ISEW ISEW 1 1 1 1 2 215 22 7 143-178 Wade (1950a) Fork length 2 33.5, 35 Wade (1950a) Fork length 4 127-175 Wade (1950a) Fork length 2 40,44 Wade (1950a) Fork length 2 40, 68.4 Wade (1950a) Fork length 1 80 Wade (1950a) Fork length 1 76.5 Wade (1950a) Fork length 18 73-112 Wade (1950a) Fork length 2 117.5-131 Wade (1950a) Fork length tnerous 150-250 Yabeetal. (1953) Fork length 6 72.0-140.0 Jones (1960) ' Length given by Jones 1 116.5 Jones (1960) is standard length. 1 162.0 Jones (1960) - Jones reported cap- 8 34.3-75.0 Jones (1960) ture of larger juve- 2 24.5, 40.6 Jones (1960) niles not included 1 96.0 Jones (1960) ' here. 1 — Strasburg(1960) 2 — Strasburg(1960) 1 — Strasburg(1960) 1 — Strasburg(1960) 2 — Strasburg (1960) — — Strasburg(1960) — — Strasburg (1960) — — Strasburg (1960) — — Strasburg (1960) — — Nakamura and Matsumoto (1967) — — Parin (1967) — 3.5-6.0 Gorbunova (1965a) Length not defined July-Sept. Hawaii ISEW — 25 — Higgins (1970) 1967 July-Sept. 21°30'- 24°45'N ISEW 24 — — Chen and Tan (1973) 1968-71 119°28'-121°30'E 03°30'- 12°00'N 102°45'-115°15'E Fig. 8). Larvae and juveniles have been reported from Hawaii (Strasburg 1960; Higgins 1970), near the Mar- quesas and Tuamotus and surrounding areas (Strasburg 1960; Nakamura and Matsumoto 1967), in the Gulf of Tonkin (Gorbunova 1965a), in the Gulf of Aden (Gor- bunova 1965b; Parin 1967), around Taiwan and adja- cent waters (Matsumoto 1959; Chen and Tan 1973), and off the coast of southern Japan (Yabe et al. 1953). These records suggest that E. affinis probably spawns through- out its range. Euthynnus alletteratus Based on the records of occurrence of postlarval and juvenile E. alletteratus, Padoa (1956) indicated that spawning in the Mediterranean occurred in the spring- time and in the summer. The summer spawning con- clusion was based on postlarval material reported on by Ehrenbaum (1924); however, Matsumoto (1959) indi- cated that the identification of E. alletteratus by Ehren- baum was erroneous. On the other hand, Belloc (1955) noted that spawning takes place in different parts of the Mediterranean chiefly in July-August. Ben-Tuvia (1957) indicated that young E. alletteratus 8 to 16 cm long are taken by "light fishing" from June to September along the Mediterranean coast of Israel, which, according to him, suggested summer spawning. Postel (1964) also in- dicated that the spawning season for E. alletteratus in the Mediterranean is in the summer (June- July-August). In the eastern Atlantic, Postel (1950) noted that the spawning season was from April to November, including a peak from June to September along the coast of Dakar, Senegal. Further south along the coast of western Africa, Marchal (1963) indicated that peak spawning took place 18 in October and November. Along the Ivory Coast, Mar- chal (1963) indicated that the spawning season is very extended, at least from October to June. He noted an in- terruption of spawning during July to September co- inciding with a cooling of the sea in the Ivory Coast area. Of interest is the series of larval tuna surveys conducted in the northwestern Gulf of Guinea in 1964 and 1965 by the Miami Laboratory, NMFS (National Marine Fish- eries Service) (Richards et al. 1969a, 1969b, 1970). The cruises were made in the winter-spring "warm season" in the Gulf of Guinea (February-April 1964 and March- April 1965) and in the summer-fall "cool season" (August-October 1964). Larval E. alletteratus were caught during the cool season as well as the warm season (Table 10). Although the surveys did not cover all the months of the year, the results, together with observa- tions made by Marchal (1963), suggest year-round spawning in the northwestern Gulf of Guinea. Around Sao Tome and Principe the spawning season extends from October to December (Frade and Postel 1955; da Costa and Frade 1958). The development of E. alletteratus gonads indicates an extended spawning season beginning in March and continuing to about November off the coast of Florida (de Sylva and Rathjen 1961). Potthoff and Richards (1970) also concluded that E. alletteratus spawns over a long period in Florida waters. They based their con- clusion on the occurrence of juveniles in the regurgitated food of seabirds in the Dry Tortugas, Fla. Klawe and Shimada (1959) reported the capture of juvenile E. alletteratus during the months of March, April, June, July, and August in the Gulf of Mexico (Table 11) and suggested reproductive activity at least during these months if not also in other months of the year. The records of other larval and juvenile E. allet- teratus shown in Table 11 suggest spawning in those areas also. Marchal (1963) concluded that in the Mediterranean and along the west coast of Africa, E. alletteratus spawns during periods of the year when the water is warmest and that this species apparently reproduces throughout its range. Euthynnus lineatus Klawe (1963) found that E. lineatus spawning in the northern part of its distribution is limited to the summer months. He also noted that farther south, E. lineatus spawns throughout the year including a possible peak in early spring (Table 12). Table 10.— Records of larval Euthynnus alletteratus in the northwestern Gulf of Guinea and off Sierra Leone (ASE't. (From Richards et al. 1969a, 1969b, 1970.) Locality No. of Locality No. of Date Lat. Long. larvae Date Lat. Long. larvae February 1964 04°20'N 08°09'W 78 ( )ctober 1964 04°23'N 01°04'E 3 04°51'N 05°30'W 1 02°53'N 01°02'W 1 05°02'N 03°53'W 2 03°38'N 02°00'W 1 04°15'N 01 o 32'W 1 04°00'N 02°38'W 4 02°45'N 01°30'W 4 04°09'N 03°10'W 5 02°51'N 01°25'W 1 I "ebruary 1965 07 o 57'N 16°53'W 1 04°20'N 01°30'W 1 06°29'N 16°28'W 5 04°30'N 00°54'W 5 06°15'N 16°29'W 1 04°34'N 00°49'W 1 09°00'N 16°02'W 1 05°31'N 00°10'E 2 06°11'N 15°30'W 1 05°28'N 00°10'E 2 07°30'N 15°00'W 2 04°48'N 00°01'E 4 I "ebruary 1965 08°30'N 15°27'W 1 04°59'N 01°00'E 15 08°14'N 15°00'W 7 04°30'N 01°30'E 3 07°26'N 15°01'W 1 March 1964 04°31'N 01°55'E 2 07°00'N 14°29'W 1 05°01'N 03°58'W 1 07°01'N 14°28'W 1 April 1964 04°32'N 05°01'W 5 P A&rch 1965 07°08'N 13°30'W 1 04°56'N 01°11'W 11 07°03'N 13°06'W 1 04°54'N 00°30'W 33 06°49'N 13°04'W 4 04°15'N 00°33'W 1 04°35'N 02°32'W 3 03°52'N 01°03'VV 1 04°06'N 02°33'W 1 02°55'N 02°04'W 10 04°20'N 01°59'W 1 03°31'N 02°04'W 10 04°08'N 01°28'W 1 August 1964 04°20'N 06°59'W 2 04°10'N 00°29'W 1 04°32'N 06°19'W 1 04°22'N 00°06'W 9 05°00'N 04°30'W 1 05°35'N 00°32'E 3 04°21'N 02°02'W 1 05°05'N 00°25'E ( 04°18'N 01 o 09'W 1 05°59'N 01°30'E 2 04°27'N 01°44'W 8 05°45'N 01°30'E 1 06°00'N 01°39'E 1 05°53'N 01°58'E 1 06°09'N 02°37'E 1 04°15'N 02°30'E 2 September 1964 02°30'N 03°50'N 07°57'W 06°41'W 1 5 'Marine area code. See Rosa (1965) 19 Table 11.— Records of larval and juvenile Euthynnus alletteratus in the Atlantic and Mediterranean. Marine area Locality code [see Rosa (1965)] Number Length (mm) Reference Date Lat. Long. Larvae Juveniles Remarks June 1920 18°00'N 64°14'W ASW 1 Matsumoto (1959) July 1920 33°07'N 77°00'W ASW 4 — ■ — Matsumoto (1959) 33°07'N 77°00'W 5 — — Matsumoto (1959) May 1921 17°55'N 64°48'W ASW 1 — — Matsumoto (1959) Nov. 1921 07°22'N 46°51'W ASW 1 — — Matsumoto (1959) 05°35'N 51°08'W ASW 1 — — Matsumoto (1959) 05°35'N 51°08'W 2 — — Matsumoto (1959) 05°35'N 51°08'W 10 — — Matsumoto (1959) 05°06'N 51°35'W ASW 1 — — Matsumoto (1959) 05°06'N 51°35'W 14 — — Matsumoto (1959) 05°06'N 51°35'W 2 — — Matsumoto (1959) May 1922 35°42'N 73°43'W ASW 5(?) — — Matsumoto (1959) June 1953 25°35'N 79°25'W ASW — 1 8.8 Klawe(1960) (') July 1954 34°35'N 75°15'W ASW — 2 25,35 Klawe (1961) (')From stomach of Euthynnus 28°59'N 88°07'W ASW — 4 27-41 Klawe and Shimada (1959) (') 28°36'N 87°58'W ASW — 4 28-33 Klawe and Shimada (1959) (') 29°05'N 88°10'W ASW — 86 21-44 Klawe and Shimada (1959) (') 27°34'N 89°00'W ASW — 3 26-38 Klawe and Shimada (1959) (') 27°58'N 88°03'W ASW — 2 76-80 Klawe and Shimada (1959) (') Aug. 1954 29°28'N 87°30'W ASW — 38 11-47 Klawe and Shimada (1959) (') 28°59'N 88°02'W ASW — 4 56-108 Klawe and Shimada (1959) (') 28°46'N 88°40'W ASW — 5 24-36 Klawe and Shimada (1959) (') 29°12'N 88°34'W ASW — 29 22-174 Klawe and Shimada (1959) (') June 1955 28°40'N 88°58'W ASW — 10 21-31 Klawe and Shimada (1959) (') Aug. 1955 28°50'N 87°50'W ASW — 4 3.5-5.3 Klawe and Shimada (1959) (') 28°50'N 87°48'W ASW — 88 30-53 Klawe and Shimada (1959) (') 28°47'N 87°57'W ASW — 16 31-55 Klawe and Shimada (1959) I 1 ) 28°45'N 87°56'W ASW — 4 6.2-8 Klawe and Shimada (1959) M 28°55'N 88°00'W ASW — 90 29-65 Klawe and Shimada (1959) (') 28°55'N 87°57'W ASW — 116 4-80 Klawe and Shimada (1959) f 1 ) 29°01'N 87°48'W ASW — 60 17-68 Klawe and Shimada (1959) (') 28°12'N 88°43'W ASW — 11 49-86 Klawe and Shimada (1959) (') 28°17'N 88°37'W ASW — 12 32-94 Klawe and Shimada (1959) (') Sept. 1955 29°27'N 86°55'W ASW — 52 24-49 Klawe and Shimada (1959) W — Gulf of Mexico ASW — 8 19-29 Klawe and Shimada (1959) (') Aug. 1956 28°50'N 87°50'W ASW — 33 21-82 Klawe and Shimada (1959) (') Oct. 1957 1 Dec. 1958 J Off Takoradi, Ghana ASE j Single ( specimen - Kazanova (1962) Length not defined July 1960 Off Dakar, Senegal ASE Up to 60 specimens per catch , » — 4.14-6.10 Kazanova (1962) Length not defined Aug. -Sept. \ 1964 | Around Cu ba ASW 20 - 3.0-5.4 Gorbunova and Salabarn(1967) Length not defined Feb. -Mar. / 06°18'N 23°20'W ASE 2 — 3.8,3.7 Zharov and Zhudova (1969) Length not defined 1963 04°40'N 24°28'W ASE 1 — 4.4 Zharov and Zhudova (1969) Length not defined < 10°00'S 34°33'W ASW 1 - 8.7 Zharov and Zhudova (1969) Length not defined 03°00'N 30°00'W ASW 1 - 4.2 Zharov and Zhudova (1969) Length not defined k 03°37'S 30°04'W ASW 1 - 4.4 Zharov and Zhudova (1969) Length not defined Apr. -July 1960-67 24°30'N 82°50'W ASW - 47 29-135 Potthoff and Richards (1970) Standard length ° C M 1964- 07°S 05°N 04°30'N 12°E \ 04°30'W > 04°30'W j ASE 4 - 4.2-10.2 Zhudova (1969a) Approximate locations Length not defined Aug. -Oct. 1964 09°20'N 19°41'W ASE No numbers given - Zhudova (1969b) Throughout Ivory Coast and ASE — Numerous — Marchal (1963) the year Ghana June-Aug. Haifa Bay ASE — Numerous 80-240 Ben-Tuvia (1957) Length not defined Aug. -Oct. Dardanelles ASE — Numerous 145-220 Demir(1963) Fork length 1959 Aug. -Sept. Sea of Marmara ASE — Numerous 180-250 Demir(1963) Fork length 1959 'Total length measured from tip of snout to shortest median ray of caudal fin. 20 Table 12. — Average numbers of Euthynnus lineatus larvae caught per hour of surface plankton tow off Cape Blanco, Costa Rica. (From Klawe 1963:465.) No. of No. of Month larvae Month larvae January 1.5 July 0.1 February 0.1 August 0.2 March 3.2 September 1.4 April 14.9 October 0.0 May 0.6 November 0.2 June 0.0 December 0.7 Records of larval and juvenile E. lineatus from the eastern Pacific and from near Costa Rica are shown in Tables 13 and 14, respectively. The records indicate the probable spawning periods and localities in the eastern tropical Pacific Ocean. 3.17 Spawn There is very little information on the fertilized eggs of Euthynnus in the literature. Delsman (1931) described the eggs of Thynnus thunnina (= E. affinis) which he had earlier identified as eggs of Scomber (= Rastrelli- Table 13. — Records of larval and juvenile Euthynnus lineatus in the eastern tropical Pacific Ocean (ISE 1 ). The lengths of the specimens were given as total or fork length in the various references listed in the table; however, both were taken in the same manner, i.e., from the tip of the snout to the shortest median ray in the caudal fin. Total or Collector Locality Number fork length (mm) or Date Lat. Long. Larvae Juveniles reference Jan. 1922 06°49'N 80°25'W 4 1 — Matsumoto (1959) 06°49'N 80°25'W 1 — — Matsumoto (1959) 06°49'N 80°25'W 1 — — Matsumoto (1959) 06°49'N 80°25'W 13 — — Matsumoto (1959) 06°40'N 80°47'W 4 — — Matsumoto (1959) 06°40'N 80°47'W 1 — — Matsumoto (1959) 06°40'N 80°47'W 1 — — Matsumoto (1959) 06°40'N 80°47'W 2 — — Matsumoto (1959) 06°40'N 80°47'W 2 — — Matsumoto (1959) 06°40'N 80°47'W 58 — — Matsumoto (1959) 06°48'N 80°33'W 1 — — Matsumoto (1959) 06°48'N 80°33'W 2 — — Matsumoto (1959) 06°48'N 80°33'W 2 — — Matsumoto (1959) 06°48'N 80°33'W 1 — — Matsumoto (1959) 06°48'N 80°33'W 1 — — Matsumoto (1959) 08°24'N 79°23'W 13 — — Matsumoto (1959) 08°40'N 79°23'W 25 — — Matsumoto (1959) Sept. 1928 07°06'N 79°55'W 2 — — Matsumoto (1959) 07°16'N 78°30'W 1 — — Matsumoto (1959) 07°55'N 79°02'W 1 — — Matsumoto (1959) Mar. 1947 08°20'N 84°10'W — 8 48-86 Schaefer and Marr (1948) 09°20'N 85°20'W — 10 29-56 Schaefer and Marr (1948) 09°10'N 85°20'W — 1 61 Schaefer and Marr (1948) May 1949 10°58'N 89°56'W — 2 7.5, 10.5 Mead (1951) 11°20'N 87°20'W — 23 14-18 Mead (1951) 12°50'N 89°40'W — 2 18,24 Mead (1951) Oct. 1951 24°35'N 112°05'W — 1 9.7 Sefton, Jr. 2 Jan. 1955 12°34'N 89°50'W — 8 25 (mean) Clemens (1956) 08°43'N 84°11'W — 34 17-38 Clemens (1956) Nov. 1955 07°42'N 79°20'W — 1 30 Eastropac Expedition 2 03°0TN 82°15'W — 6 27-38 Eastropac Expedition 2 Dec. 1955 11°48'N 88°25'W — 1 46 Eastropac Expedition 2 Nov. 1955 08°31.3'N 79°32'W 2 — — Klawe (1963) Aug. 1956 26°04.5'N 112°48'W 1 — 7.0 LaJollaLab.,NMFS 2 Sept. 1956 15°05'N 93°54'W — 3 15-27 Klawe (1963) Oct. 1956 12°51'N 93°05'W — 1 51 Klawe (1963) Nov. 1956 14°00'N 96°11'W — 1 30 Schaefer and Shimada 2 Feb. 1957 17°24'N 102°04'W — 1 21 Renner and Hark 2 Aug. 1957 29°12'N 115°39'W — 1 — LaJollaLab.,NMFS 2 31°11'N 114°15'W — 2 29.5, 353 LaJollaLab., NMFS 2 May 1958 05°34'N 81°29'W — 1 60 Klawe (1963) 08°28'N 84°21"W 1 — — Klawe (1963) 15°15'N 95°23'W 11 — — Klawe (1963) June 1958 18°44'N 104°21'W — 5 20-27 Klawe (1963) 17°49'N 103°38.5'W — 99 7.5-45 Klawe (1963) 21°36'N 106°44'W — 3 18-48 Klawe (1963) 16°39'N 100°05'W 1 — — Klawe (1963) 17°24'N 101°25'W 6 — — Klawe (1963) 18°44'N 104°21'W 1 — — Klawe (1963) 21 Table 13.— Continued. Total or Collector Locality Number fork length (mm) or Date Lat. Long. Larvae Juveniles reference Nov. 1958 14°56.5'N 93°06.5'W 11 — — Klawe (1963) 15°39'N 93°59.5'W 1 — — Klawe (1963) 14°18'N 95°02.8'W 1 — — Klawe (1963) 15°02'N 95°07.5'W 1 — — Klawe (1963) 14°21'N 97°01'W 3 — — Klawe (1963) 14°21'N 97°01'W 24 — — Klawe (1963) 15°31'N 97°44'W 5 — — Klawe (1963) Dec. 1958 15°31'N 97°44'W 15 — — Klawe (1963) 15°36'N 99°23.5'W 1 — — Klawe (1963) Jan. 1959 15°29.5'N 98°32.5'W 4 — — Klawe (1963) 15°29.5'N 98°32.5'W 4 — — Klawe (1963) Feb. 1959 19°46'N 105°44'W 5 — — Klawe (1963) Apr. 1959 08°12'N 83°15.5'W — 6 12-18 Broadhead and Chatwin 2 08°12'N 83°17'W — 1 7.5 Broadhead and Chatwin 2 08°15'N 83°23'W — 6 13-28 Broadhead and Chatwin 2 Sept. 1959 15°39'N 97°00'W 2 — — Klawe (1963) 14°20'N 95°59'W 6 — — Klawe (1963) 14°20'N 95°59'W 6 — — Klawe (1963) 14°54.8'N 95°07.1'W 36 — — Klawe (1963) 14°21.5'N 94°01'W 5 — — Klawe (1963) 16°28'N 99°32.5'W 2 — — Klawe (1963) Feb. 1961 12°35'N 93°40'W — 3 7.5-9.5 Vann 2 Oct. 1966 Entrance, Gulf of 2 — — Klawe etal. (1970) California Nov. 1966 Entrance, Gulf of 3 — — Klawe etal. (1970) California OffTres Marias Is. 1 — — Klawe etal. (1970) Dec. 1966 Entrance, Gulf of 1 — — Klawe etal. (1970) California 'Marine area code. See Rosa (1965). 2 As reported in Klawe (1963). ger) kanagurta. Delsman noted that the egg diameters were 0.85 to 0.95 mm and that the diameter of the oil globule ranged from 0.21 to 0.24 mm. Sanzo (1932) de- scribed some fertilized eggs which he tentatively identi- fied as belonging to Euthynnus alletteratus. The eggs were buoyant, spherical, and transparent, and were about 1.08 mm in diameter with an oil globule 0.28 mm in diameter. The dimensions of the fertilized eggs were very similar to that of A uxis and Thunnus eggs, but the embryos did not show yellow pigmentation as in those species. The yolk sac was rich in black pigment. Houde and Richards (1969) reported on the collection of some fertilized eggs which were later determined to be from E. alletteratus. The eggs were collected from May through August 1969 in the Straits of Florida off Miami and returned to the laboratory for incubation. In a successful attempt at hatching some of the fertilized eggs, examination of the resulting larvae reared to 12 days past hatching revealed that the larvae were those of E. alletteratus. They noted that the larvae hatched within 12 h of collection and probably within 24 h after the eggs were fertilized. They did not include a descrip- tion of the fertilized eggs. Calkins and Klawe (1963) stated that the fertilized eggs of E. lineatus are pelagic but they had never been specifically identified in plankton collections. 3.2 Preadult phase 3.21 Embryonic phase Euthynnus af finis Delsman (1926), as stated earlier, described some fer- tilized eggs of Scomber (= Rastrelliger) kanagurta which he later reidentified as Thynnus thunnina (= E. affinis). He noted that the eggs took less than 24 h to hatch. Dels- man's drawing of a newly hatched larva indicates a size of approximately 2.1 mm at hatching. He counted a total of 39-41 "myotomes" in larvae of various stages of de- velopment (Fig. 11). Whether these were actually larvae of E. affinis has not been verified. Euthynnus alletteratus Houde and Richards (1969) collected the fertilized eggs of E. alletteratus and were successful in hatching the eggs and rearing the larvae up to 18 days past hatching. The larvae were slightly less than 3 mm long at hatching. The newly hatched larvae had a large yolk sac that con- tained a single prominent oil globule, the eyes were un- pigmented, and the mouth and gut were not functional. The yolk was absorbed, the eyes became pigmented, and 22 Table 14. — Larval and juvenile Euthynnus lineatus captured off Cape Blanco, Costa Rica (ISE 1 ). (From Klawe 1963, table 5.) Location from Cape Blanco N jmber Total length (mm) Date Larvae Juveniles Nov. 1958 20miS 1 6.5 20miS 1 — 9.0 20 mi SSW 1 — 6.0 20miSSW 2 — 5.0 Jan. 1959 20miS — 8 21-39 20miS — 43 14-25 Feb. 1959 20miS — 8 25-50 20miS 1 — 5.0 Mar. 1959 20miS 3 — 5.1-6.7 20miS 1 — 6.7 5 miSE 5 miSE 2 6 — 6.2,8.2 5.2-9.2 5 miSE 1 — 5.3 Apr. 1959 20miS — 4 11-25 5 miSE — 77 16-25 20 mi S 2 — 6.5-7.7 20miS 7 — 5.0-8.2 20 mi SE 12 — 4.1-7.1 5 miSE 23 — 4.5-7.5 5 miSE 25 — 4.4-7.5 5 miSE 12 — 4.4-7.2 5 miSE 88 — 4.4-14.2 May 1959 lOmiSE 10 mi SE 5 11 16-25 5.5-8.0 10 mi SE 1 — 8.5 10 mi SE 2 — 6.0-13.0 June 1959 lOmiW — 2 ca.17 Aug. 1959 12miSE 3 — 4.6-8.8 6 miSE — 3 15-17 Sept. 1959 20miS 4 — 4.8-5.7 lOmiS 5 — 6.1-7.4 lOmiS 4 — 5.0-7.3 lOmiS 5 — 4.4-7.5 Nov. 1959 20miS — 4 11.5-53 20miS 1 — 4.4 Jan. 1960 lOmiS 9 — 4.1-5.5 lOmiS 2 — 4.6-4.8 Feb. 1960 20 mi SSW — 1 18 Mar. 1960 lOmiS — 12 15-28 20miS 6 — 3.3-6.3 20miS 19 — 4.3-8.6 lOmiS 6 — 3.7-6.7 lOmiS 4 — 6.6-8.3 May 1960 20miS lOmiS — 14 6 13-21 9.5-24 lOmiS 1 — 6.5 July 1960 lOmiS — 4 13-17 lOmiS — 62 10-24 lOmiS 1 — 7.0 Aug. 1960 lOmiS 1 — 6.0 20miS — 1 19 lOmiS — 3 12-18 Sept. 1960 Oct. 1960 lOmiS lOmiS 1 51 12.5-24 7.5 Marine area code. See Rosa 1965. the mouth and gut were functional within 48 h after hatching. Euthynnus lineatus No information. 3.22 Larvae and adolescent phases The larvae and juveniles of all three species of Euthyn- nus have been described in detail (e.g., Schaefer and Marr 1948; Wade 1950a; Mead 1951; Matsumoto 1958, 1959; Jones 1960). The following descriptions of young Euthynnus are taken primarily from the above refer- ences. Euthynnus af finis The smallest specimen identified by Matsumoto (1958) as E. affinis measured 4.6 mm TL (Fig. 12a). The head length is moderate (33.9% TL), there are 40 myo- meres, and the abdominal sac is nearly triangular. The mouth is fairly large (about 71.9% of the head length) and contains 12 teeth on the upper jaw and 9 teeth on the lower jaw. The distance from the tip of the snout to the anterior edge of the orbit is almost equal to the orbit diameter. Three long spines are present on the posterior edge of the preopercle; the longest spine is the one at the angle. Generally, a single chromatophore is found at the middle of the lower jaw and at the symphysis of the pec- toral girdle. The median fins show very little development; there are 4 or 5 rays in the caudal fin and only strong striations representing rays in the incipient anal and dorsal fins. The pelvic fins are undeveloped and the pectoral fins show only striations. There are 13 and 15 teeth in the upper and lower jaws, respectively, and the preopercular spines have increased to 6 in a 5.5 mm TL specimen (Fig. 12b). Five short spines are present in the first dorsal fin and about nine rays in the caudal; the other median fins and the pectorals still show only strong striations and the pelvic fins are just emerging as small buds. The single chromatophore at the middle of the mandi- ble and that at the pectoral symphysis are still evident. A 7.6 mm TL specimen exhibits some striking changes, particularly in pigmentation. A series of four or five chro- matophores is present on the anterior half of the mandi- ble and the first dorsal fin is almost completely pigmented. The head comprises 39.8% of the total length and the snout length is much greater than the diameter of the or- bit. About 16 teeth are present on both the upper and lower jaws, and 7 spines are noticeable on the posterior edge of the preopercle. There are 8 spines in the first dorsal fin; the length of the longest spine is less than half the distance between the dorsal fin insertions. The second dorsal and anal fin rays are further developed and, although the rays are not clearly evident, about 11 radials in the second dorsal and 12 in the anal are present. The first 7 dorsal and 6 anal finlet radials are also evident. There are 9 + 9 rays in the caudal fin and the pelvic fins are complete with 1 spine and 5 rays; about 5 rays are noticeable in the pectoral fins. 23 12 + 28 Newly hatched larva, X 4.0. IO + 30 Larva of the next morning, X 40 IO+29 I-irva of the Hccond night, X 40. 10+31 Larva of the second morning, with yolk completely absorbed and eyes black, X 4 ft - Figure 11. — Larvae of Euthynnus affinis. (From Delsman 1926, figs. 3-6.) The first dorsal fin is heavily pigmented, and the pigmentation at the tip of the snout is more extensive in a 9.6 mm TL specimen (Fig. 12d). Chromatophores now extend over two-thirds of the length of the mandible and the chromatophore at the symphysis of the pectoral gir- dle still persists. The first dorsal fin now has 13 spines and the length of the longest spine is greater than half the distance be- tween the dorsal fin insertions. There are 13 rays in the second dorsal and anal fins. Figure 12. — Euthynnus affinis larvae: (a) 4.6 mm; (b) 5.5 mm; (c) 7.6 mm; (d) 9.6 mm. (From Matsumoto 1958, figs. 15-17.) The body length, total or fork length, was measured from the tip of the snout to the fork of the tail when the tail was forked, and to the tip of the longest ray when the tail was not forked. 24 25 Figure 13.— Juvenile Euthynnus affinis: (a) 24.5 mm SL; (b) 33.5 mm FL; (c) 56.6 mm SL; (d) 67 mm FL; (e) 96.0 mm SL; (f) 110 mm FL; (g) 156 mm FL. (From Wade 1950a, figs. 10-13; Jones 1960, figs. 1-3.) Wade (1950a) and Jones (1960) described juvenile E. affinis ranging in length from 24.5 mm SL (standard length) to 156 mm FL (Fig. 13). In the 24.5 mm SL speci- men (Fig. 13a), all the larval characters are lost except for the vestiges of the preopercular spines (Jones 1960). The color of the body in the 24.5 mm SL and in the 33.5 mm FL (Fig. 13b) specimens is light brown dorsally and becomes paler toward the midline. A dark longitudinal band is present along the lateral midline and ventrally the body is pale. According to Wade (1950a) the color of the body and the head darkens as the fish grows larger and about 9 to 13 darker vertical bars begin to develop above the lateral midline on specimens about 60 mm FL. The first dorsal has 16 spines and the posterior spine nearly reaches the base of the second dorsal. There are 12 26 to 14 rays (mostly 13) in the second dorsal and 13 or 14 rays in the anal fin. There are 8 dorsal and 7 anal finlets. The gill raker count on a 35 mm FL specimen was 4 + 1 + 20 and increased to (7-8) + 1 + (22-23) in specimens of 127 to 175 mm FL (Wade 1950a). Euthynnus alletteratus See section 3.21. In a 4.6 mm TL specimen of E. alletteratus (not fig- ured), no visible indication of spine or ray development is evident in the unpaired fins. The future fins are repre- sented by a continuous membrane which starts near the nape and extends around the caudal end to the anal opening. There are 40 myomeres including the urostyle; the urostyle is incompletely developed and extends pos- teriorly in line with the longitudinal axis of the body. Chromatophores are present at the pectoral girdle symphysis and immediately anterior to the anal opening along the midventral line. There are about 3 chromato- phores over the forebrain and about 12 over the mid- brain and a row of 3 or 4 well -spaced chromatophores is evident over the middle two-thirds of the length of the lower jaw (Matsumoto 1959). A 5.5 mm TL specimen (Fig. 14a) shows the develop- ment of four short spines in the first dorsal fin. The un- paired fins are beginning to develop, and the urostyle has turned upward. Chromatophores along the margin of the 27 Figure 14.— Euthynnus alletteratus larvae: (a) 5.5 mm; (b) 7.5 mm; (c) 9.3 mm. (From Matsumoto 1959, figs. 8-10.) (See Fig. 12 for definition of body length.) lower jaw have increased and cover the anterior two- thirds of the jaw length. Nine chromatophores are pres- ent on the midventral line from the anal fin origin to the caudal peduncle (Matsumoto 1959). A 7.5 mm TL specimen (Fig. 14b) has 9 very long spines in the first dorsal fin. There are 12 or 13 rays in the second dorsal, 14 rays in the anal, and about 17 rays in the caudal fin. 28 Pigmentation is increased on the first dorsal fin and about 13 well-scattered chromatophores are present on the outer two-thirds of the fin between the first and seventh spines. The chromatophores along the lower jaw have increased and now appear closer together. The pigmentation along the midventral edge of the body con- sists of about 11 regularly spaced chromatophores although some specimens may have as many as 15 (Matsumotol959). The most noticeable change in a 9.3 mm TL specimen (Fig. 14c) is the extremely long spines in the first dorsal fin. Similar to E. lineatus of comparable size, the length of the longest spine is about equal to the body depth measured at the origin of the second dorsal fin. The sec- ond dorsal and anal fins have 13 rays. The posterior edge of the caudal fin now shows signs of becoming forked and the ventral fins are beginning to enlarge. Pigmentation on the outer half of the first dorsal fin membrane has in- creased; there are 22 chromatophores extending over 8 interspinous membranes (Matsumoto 1959). Matsumoto (1959) noted many changes in a 10.6 mm TL and a 11.5 mm TL specimen (not figured). Both specimens have completely developed dorsal and anal fins including 16 spines and 13 rays in the dorsal, fol- lowed by 8 finlets, and 14 rays in the anal followed by 7 finlets. The caudal fin is more clearly forked and the pelvic fins are longer. The 11.5 mm TL specimen has 20 + 19 vertebrae. An increase in pigmentation is evident in several places. The lower jaw bears two rows of chro- matophores (the larger specimen has a third row) and the upper jaw has a single row of chromatophores along two- thirds of its length. Matsumoto (1959) also described postlarval and juve- nile E. alletteratus ranging in length from 12.0 to 58.0 mm TL (Fig. 15). The pigmentation along the dorsal and ventral edges of the body and along the midlateral line noted in the 10.6 and 11.5 mm TL specimens was also evident in the 12.0 mm TL specimen (Fig. 15a). Distinc- tive changes occurred between the 12.0 and 18.5 mm TL specimens (Fig. 15b). The abdominal sac was more elongate and the anus was more posteriorly placed in the larger specimen. The head parts, particularly the mouth, appeared smaller in relation to the total length and the fins and finlets were more clearly defined. The outline of the dorsal fin in the 26.0 mm TL specimen (Fig. 15c) resembles that of an adult and the body is narrower, rela- tive to the total length than in the 18.5 mm TL speci- men. For specimens larger than 26.0 mm TL the only noticeable change is in the increased pigmentation on the body. At about 40 mm TL one to three very faint spots or ventral bars appear along the dorsal third of the body. The number of bars increases to about 10 in a 58.0 mm TL specimen (Fig. 15d) and to 13 on a 94.3 mm TL fish (not figured). Richards and Dove (1971) described in detail the inter- nal development of young E. alletteratus ranging in stan- dard length from 3.5 to 24.0 mm. Anatomical features of E. alletteratus were described and compared with those of K. pelamis, Thunnus albacares, T. obesus, T. thyn- nus, T. alalunga, T. atlanticus, and Auxis spp. The fol- lowing anatomical features were examined: the sensory organs including the eyes, olfactory organs and acoustico-lateralis systems, the nervous system (brain), swim bladder, kidney, gonads, liver, pancreas, spleen, digestive system, cardiovascular system, gills, skeleton, musculature, and pigmentation. Potthoff and Richards (1970) also made observations on the development of the axial skeleton of E. alletteratus and also computed a re- gression equation to estimate the standard length of a specimen based on the length of the vertebral column. The equation is, SL = 3.66 + 1.22 VL, where SL is stan- dard length in millimeters, and VL is vertebral column length in millimeters. Euthynnus lineatus The smallest larval E. lineatus identified by Matsu- moto (1959) measured 5.0 mm TL (Fig. 16a). The head is relatively large (about 37% TL) and the mouth is also large and contains about eight teeth on each side of both jaws. As in the other species of Euthynnus at the same stage, the abdominal sac is short and triangular, and the anus is located near the middle of the body. Spines and rays are undeveloped in all the fins. There are 38 or 39 myo- meres including the urostyle. Chromatophores are present at the symphysis of the pectoral girdle and anterior to the anal opening. There is no pigment on the lower jaw at this stage of develop- ment (Matsumoto 1959). There are 5 short spines in the region of the first dorsal fin and posterior to these, 2 more are beginning to de- velop in a 6.0 mm TL specimen (Fig. 16b). The second dorsal and anal fin rays are still poorly developed and are difficult to distinguish; there are 17 rays in the caudal fin. Three or four chromatophores can be seen near the middle of the lower jaw (Matsumoto 1959). In a 7.1 mm TL specimen (Fig. 16c) the first dorsal fin has 7 definite spines, of which the 6 anterior ones are slightly greater in length. Three additional weak spines are beginning to develop but the fin rays are poorly formed. The caudal fin is beginning to fork and has 18 well-developed rays. There are some striking changes in pigmentation in this specimen. The first dorsal fin between the second and sixth spines now has six large chromatophores. Chro- matophores are present at the tips of the upper and lower jaws and seven more are found along the anterior two- thirds of the lower jaw (Matsumoto 1959). Compared with the 7.1 mm TL specimen, a 9.3 mm TL specimen (Fig. 16d) has a well-developed dorsal fin. It has 12 well-developed spines of which the longest is about 78% of the body depth at the origin of the second dorsal fin. The second dorsal fin consists of 11 rays and the anal fin 12 rays. The pelvic fins are nearly complete in development and the pectorals have about 14 distinct rays. The first dorsal fin is pigmented over the first eight interspinal membranes; the pigmentation is generally concentrated on the outer two-thirds of the fin (Matsu- moto 1959). 29 30 The abdominal sac is more elongate and the anal open- ing only slightly anterior to the anal fin origin in a 10.6 mm TL postlarval E. lineatus (Fig. 17a). The dorsal fin consists of 15 spines and 12 rays, and there are 8 dorsal finlets; the anal fin consists of 11 rays and there are 7 anal finlets (Matsumoto 1959). The 18.6 mm TL juvenile (Fig. 17b) is already similar in body shape to larger juveniles due mostly to a gradual reduction in the head depth relative to body length and to the elongation of the abdominal sac, wherein the anal opening is closer to the anal fin origin. The fins and finlets are more clearly defined in the 18.6 mm TL specimen. The dorsal fins have the full adult complement of 15 spines and 12 rays, followed by 8 finlets. The anal fin also has the full adult complement of 12 rays followed by 7 finlets. The caudal fin is well de- veloped and more deeply forked, the pelvic fins are longer, and the pectorals have 24 completely formed rays which are comparable to the fully developed fins (24-26 rays) of the adults (Matsumoto 1959). In the 21.0 mm TL specimen (Fig. 17c), except along the area of the lower jaw, the pigmented areas are more widespread (Matsumoto 1959). 3.3 Adult phase 3.31 Longevity See sections 3.43 and 4.13. The maximum size and longevity of E. affinis are not well defined. Kishinouye (1923) stated that E. affinis from Japanese waters grow to be 60 cm and 3.5 kg, and that on rare occasions, specimens over 100 cm long and 10 kg in weight are found. Ommanney (1953) reported that the largest E. affinis caught during a survey in the Mauritius-Seychelles area was a specimen 87 cm long, which weighed 8.6 kg (19 lb). Around the Marquesas Islands, E. affinis as large as 79 cm have been taken on surveys conducted by the NMFS Honolulu Laboratory. Landau (1965) estimated the age of the oldest fish from a sample collected in the Red Sea as 6 yr old. The fish was 62 cm SL and weighed a little over 5 kg ( 1 1 lb) . Fowler (1936) indicated that E. alletteratus from the West Indies grow to 122 cm. The largest specimen measured by Postel (1956) in the Mediterranean Sea off Tunisia was 101.5 cm, but he noted seeing many ex- ceeding a meter in length. In the tropical eastern Atlan- tic, the largest specimen measured by Postel (1955a) in Senegal was 94.6 cm. Landau (1965) noted that the oldest E. alletteratus in her Mediterranean samples be- longed to age group X and was estimated to be about 86 cm SL (defined as the distance from snout to insertion of caudal fin). The world record sport catch for E. allet- teratus is a specimen 92.07 cm long and weighing 12.24 kg (20 lb) (International Game Fish Association un- dated). Figure 15.— Postlarvae and juvenile Euthynnus alletteratus: (a) 12.0 mm (b) 18.5 mm; (c) 26.0 mm; (d) 58.0 mm. (From Matsumoto 1959, figs. 11-14.) (See Fig. 12 for definition of body length.) There is no information on the longevity of E. lineatus. 3.32 Hardiness Not much is known on the hardiness of the three spe- cies of Euthynnus. In establishing tunas in tanks and ponds for experimental purposes, Tester (1952a) noted that small E. affinis 0.4 to 1.4 kg (1-3 lb) became es- tablished in these enclosures more readily than yellow- fin tuna, T. albacares. Once a school of E. affinis be- came established, newly introduced fish started to feed during the second day of confinement. In the experi- mental tanks maintained by NMFS in Honolulu, E. af- finis have survived for more than 14 mo (Magnuson 1965). Stevens and Fry (1971) took body temperatures of E. affinis that had been in captivity for 2 yr. Calkins and Klawe (1963) stated that the hardiness of E. lineatus is similar to that of other tunalike fishes and that "They are hardy enough to be successful in their natural environment, but they can only stand a minimum of handling." 3.33 Competitors The competitors of E. affinis in east African waters in- clude skipjack tuna, small yellowfin tuna, Auxis thazard, and a carangid, Megalaspis cordyla (Williams 1963). These fishes school together with E. affinis off east Africa in the Indian Ocean. In waters around Sri Lanka, E. af- finis are found in schools together with A. thazard, and presumably these two species are direct competitors for food (Williams 1963). Marchal (1963) stated the E. alletteratus competes with species with which it is found such as A. thazard and S. sarda. He also suggests the dolphins (Delphinus) and other cetaceans, Grampus and Globicephala, as probable competitors. In the eastern tropical Pacific, E. lineatus is found in close association with yellowfin tuna, skipjack tuna, and dolphin fish (Coryphaena) that undoubtedly compete with it for food (Calkins and Klawe 1963). 3.34 Predators In east Africa, E. affinis have been found in the stom- achs of longline-caught striped marlin, Tetrapturus audax, and sharks, Carcharhinus spp. (Williams 1963). Predators of E. alletteratus include various species of sharks, Carcharhinus spp. and Galeocerdo spp., large yellowfin tuna, and Istiophorus spp. (Marchal 1963). Euthynnus lineatus have been found in the stomachs of yellowfin tuna (Alverson 1963). Calkins and Klawe (1963) stated that the large billfishes undoubtedly prey on E. lineatus. 3.35 Parasites, malities diseases, injuries, and abnor- Silas (1967a) and Silas and Ummerkutty (1967) made detailed surveys on parasitism in Euthynnus and other 31 32 Figure 17. — Postlarval and juvenile Euthynnus lineatus: (a) 10.6 mm; (b) 18.6 mm; (c) 21.0 mm. (From Matsumoto 1959, figs. 5-7.) (See Fig. 12 for definition of body length.) scombrids. They found that the three species of Euthyn- nus were parasitized by various copepods, digenetic trematodes, and monogenetic trematodes (Table 15). Figure 16. — Euthynnus lineatus larvae: (a) 5.0 mm; (b) 6.0 mm; (c) 7.1 mm; (d) 9.3 mm. (From Matsumoto 1959, figs. 1-4.) (See Fig. 12 for definition of body length.) Calkins and Klawe (1963) also found that E. lineatus was parasitized by a trematode Hirudinella marina, which was found in the stomach. Postel (1954) also listed the parasites of E. alletteratus (Table 16). Thomas (1967) described a new parasitic copepod, Caligus krishnai, from the gills of E. af finis. 33 Table 15. —Parasites of Euthynnus. (Modified from Silas 1967a; Silas and Ummerkutty 1967.) Parasites Host Copepods Monogenetic trematodes Digenetic trematodes Euthynnus alletteratus Euthynnus affinis Euth\nnus lineatus Caligus bonito Caligus coryphaenae Pseudocycnus appendiculatus Ceratocolax euthynni Bomolochus anonymous Caligus coryphaenae Caligus regalis Pseudocycnus appendiculatus Caligus bonito Caligus ambly genitalis Caligus euthynnus Caligus asymmetricus Caligus sauala Caligus productus Caligulus longispinosus Caligus coryphaenae Caligus macarovi Capsala maccallumi Capsala manteri Hexostoma macracanthum Capsala goun 'Pricea minimae 'Hexostoma euthynni Allopseudaxine katsuwonis Allopseudaxine macrova Hexostoma euthynni Dinurus scombri Lecithochirum texanum Rhipidocotyle capitatum Rhipidocotyle nagatyi Sterrhurus monticelli Tergestia laticollis Rhipidocotyle septapapillata lecithochirum magnaporum 'Lecithochirum microstomum Hirudinella marina 'Lecithochirum magnaporum 'Lecithochirum microstomum Doubtful record. Table 16. — Parasites of Euthynnus alletteratus. table 2.) (From Postel 1954, Location of Parasite Life stage infestation Callitetrarhynchus gracilis Plerocercoid larvae Body cavity Otobothriidae Plerocercoid larvae Pyloric caeca Radmorhynchus pristis Adult Stomach Sterrhurus sp. Adult Stomach Hirudinella clavata Adult Stomach Hexostoma thunninae Adult Gills Hexostoma macracanthum Adult Gills Nerocila orbignyi Adult Ventral finlets form maculata 3.36 Physiology, biochemistry, etc. Carey et al. (1971) stated that the tunas, including E. alletteratus, have evolved a countercurrent heat- exchange mechanism for conserving metabolic heat and raising body temperature. They determined that the temperature of one specimen of E. alletteratus was 31.2°C. The surface water temperature was 19.9°C; thus, the body temperature of the fish was 11.3°C higher than the surrounding water temperature. Stevens and Fry (1971) determined the body tempera- tures of two E. affinis held in captivity for 2 yr. They found that captivity reduced the excess temperature (de- fined as the body temperature minus ambient water temperature) of E. affinis. Graham (1973) determined the thermal profile of E. lineatus, which uses a centrally located vascular heat-exchange mechanism similar to that of E. alletteratus to maintain core body tempera- tures warmer than ambient temperature of seawater. He also described the structure of the central heat-exchange mechanism and the effect of temperature changes in blood-gas relationships in E. lineatus. Graham found that a warm central core in E. lineatus was related to the distribution of red muscle. The warmest body tempera- tures occurred along the vertebral column between the first and second dorsal fins. The heat-exchange mechan- ism in E. lineatus was composed of the dorsal aorta, the posterior cardinal vein, and a large vertical rete. The dor- sal aorta was embedded in the posterior cardinal vein and was thus completely bathed in venous blood. Graham found that similar to the situation in bluefin tuna, T. thynnus, the oxygen-carrying capacity of hemo- globin was unaffected by changing blood temperature. Graham (1975) discussed the adaptive significance of elevated body temperatures in scombrid fishes. He reit- erated the observation made by Carey et al. (1971) that the principal advantage of a high and fairly constant body temperature is facilitation of continuous swimming by increasing the frequency of muscular contractions, thus increasing available swimming power. Graham (1975) also observed that warm-bodied fishes probably achieve a marked independence from environmental temperature that permits them to make rapid hori- zontal and vertical migrations without the necessity of thermal acclimation. Aspects of gas exchange in E. affinis have also been de- termined (Stevens 1972). The perfusion rate of the gills was determined to be 1.77 liter/min per kg (mean) and ranged from 1.55 to 1.88 liter/min per kg in three trials on a 2.26 kg specimen. The head loss in centimeters of water averaged 1.8. The calculated resistance to water flow of- fered by the gills averaged 1.03 cm of water/min per kg per liter and ranged from 0.90 to 1.20. Oxygen uptake was determined to be 503 mg/h per kg (mean) and ranged from 400 to 643. The calculated utilization (fraction of oxygen removed from the water) averaged 0.79 and ranged from 0.69 to 0.95. Rivas (1953) determined that scombrid fishes, in- cluding Euthynnus, possessed a pineal apparatus. He gave a description of the pineal apparatus and hypothe- sized that it might function as a light receptor to control phototactic movements of the fish. Support for Rivas' hypothesis was provided by Murphy (1971) who investi- 34 gated the pineal organ in bluefin tuna and found that the bluefin tuna's pineal organ had sensory cells possessing the structural characteristics of vertebrate retinal photo- receptor cells. He concluded that the pineal organ in bluefin tuna serves as a photoreceptor which receives ex- ternal light stimuli and that such stimuli may travel from the pineal organ to a site of action via an apocrine secretion moving through capillaries or more likely by impulses transmitted by the pineal nerve. Magnuson (1970) made a detailed study of the hydro- static equilibrium of E. affinis. This study was based on morphometric and body density measurements of fish 31.6 to 67.8 cm long and from observations on the swim- ming behavior of fish about 42 cm long held in tanks. Variations in required lift under various conditions of seawater density, density of fish, and amount of food in the gut were evaluated. Magnuson (1970) also estimated the effectiveness of each lifting hydrofoil on E. affinis in terms of the percentage of the total lift it produced, its surface loading, and its coefficient of lift. He used all these parameters to develop a model which predicted the minimum speed required for hydrostatic equilibrium. In a later paper Magnuson (1973) tested this model to see if it predicted the swimming speeds of a large number of scombroid fishes, including E. affinis; considered the "adaptive radiation in the morphology especially of the gas bladder and pectoral fins which together with swimming speed contribute to the mechanism by which scombroids maintain hydrostatic equilibrium"; and con- sidered problems associated with maintaining hydro- static equilibrium by large body size. 3.4 Nutrition and growth 3.41 Feeding Observations on various aspects of feeding and related observations have been made on Euthynnus. Bullis and Juhl (1967) observed what they called "phalanx orienta- tion" in the feeding behavior of E. alletteratus near the Grenadine Islands in the Lesser Antilles. This pattern of orientation was observed as the E. alletteratus were apparently feeding on a large group of dwarf herring, Jenkinsia lamprotaenia, which had collected directly un- der a floating night light. The phalanx developed by a single fish being joined by another and then by a third fish. This phalanx took the form of a tightly packed three-fish aggregation evenly aligned side by side. The phalanx attacked the ball of dwarf herring without alter- ing formation. The observers noted that the attack on the dwarf herring did not start until the phalanx had been formed. During the course of feeding, additional E. allet- teratus were seen to join the phalanx until it was esti- mated that the phalanx contained 14 or 15 fish of about the same size. Wicklund (1968) reported on daylight feeding patterns of E. alletteratus in Florida waters. He observed a school of 20 and a group of 4 fish feeding on bigeye scad, Selar crumenophthalmus, and herring, Clupea sp. Wicklund observed E. alletteratus moving toward the herring at which time the herring moved to the bottom and mixed with the scad. The E. alletteratus attacked when all the herring and scad were tightly packed against the bottom. In their attacking maneuver, the fish swam downward toward their prey with a great burst of speed and in the instant before reaching bottom they turned sharply parallel to the bottom, stirring up clouds of sediment. Wicklund noted that the E. alletteratus took their prey at this point or a fraction of a second later, and noted that the fish's jaws could be heard snapping audibly. The feeding continued all day, presumably in the same man- ner. The E. alletteratus left the area in the evening at 1800 and returned at 1030 the next day. Wicklund's (1968) observations have similarities and differences from observations made by Hiatt and Brock (1948). The latter observed a group of three E. affinis herding a closely packed school of several hundred scads, Decapterus sanctaehelenae, over a large coral head in Rongerik lagoon in the northern Marshall Islands. They noted that the three E. affinis "... usually followed the school of scads rather closely, with one tuna at each rear flank of the school and the third lagging behind them. Now and then the scads would turn off to one side, at which time the tuna on that side could move forward swiftly and herd them back into line." On one occasion, Hiatt and Brock (1948) saw a stray scad eaten by the rearmost E. affinis. Except for this incident, the E. affinis did not make any attempt to prey on the scads during the 3-h observational period. Wicklund's observa- tions were similar to Hiatt and Brock's in that in both in- stances the Euthynnus forced the prey into tightly packed schools. However, the E. alletteratus observed by Wicklund (1968) aggressively attacked their prey whereas the E. affinis observed by Hiatt and Brock (1948) merely picked off the stragglers. In this regard, Wicklund's observations are more similar to those made by Kishinouye (1923). Kishinouye (1923) noted that E. affinis were voracious feeders, and described their feeding method as darting swiftly into a school of small fish and scattering them. As Kishinouye (1923) stated, however, the feeding habits of E. affinis may vary throughout the year. Presumably, this could also be true for the other species of Euthynnus. Walters (1966) studied the filter feeding of E. affinis by means of high-speed motion pictures. He showed that E. affinis traveled an average of 5.9 body lengths/s while feeding and observed a maximum speed of 10.0 body lengths/s. He found no change in speed and no increase in swimming effort as the fish opened its mouth and dis- tended the orobranchial chamber to engulf its prey. Walters (1966) observed that the feeding mechanism is drag free and that E. affinis feeds by swimming over its prey rather than by sucking it into its mouth. He also pointed out that E. affinis, and scombrid fishes in gen- eral, are facultative filter-feeders in that they are able to feed in open water upon swimming organisms that are minute in comparison to the size of the predator, and noted the high gill-raker counts in these species to sup- port his statement. 35 Magnuson and Heitz (1971) determined that the mean gill-raker gap for E. af finis was 1.4 mm and the filtering area of the first gill arch was 650 mm 2 . They noted that in terms of gill-raker gap, E. affinis was intermediate (ranked fifth, going from small to large) compared with Katsuwonus pelamis, Auxis rochei, A. thazard, Scom- ber japonicus, Thunnus albacares, T. alalunga, T. obesus, Sarda chiliensis, S. orientalis, Coryphaena equiselis, and C. hippurus, ranked from small to large, respectively. Magnuson and Heitz (1971) related the gill- raker apparatus to food selectivity among these fishes and noted that despite the varied diet of scombrid fishes, selectivity in terms of size does exist in the scombrids. They observed that within a species, larger fish fed on relatively fewer crustaceans and more fishes. 3.42 Food Observations on the diet of Euthynnus from various lo- calities suggest that these fishes feed primarily on what- ever is available at any particular place and time. As an example Ronquillo (1953) found that E. affinis fed about equally on crustaceans (56.2% by number) and fishes (43.8% by number) in Philippine waters. Ronquillo (1953) found no squids in the stomachs. Around Hawaii Tester and Nakamura (1957) also found that squids were negligible in the diet of E. affinis, but unlike the Philip- pine area, fishes were much more important (91.8% by volume) than crustaceans (8.2% by volume). In the In- dian Ocean, Kumaran (1964) found that squids (56.5% by volume) were most important, followed by fishes (38.3% by volume), and crustaceans (5.2% by volume) were the least important. For E. alletteratus in the Mediterranean Sea, Oren et al. (1959) found that crustaceans (63% by number) were most important followed by fishes (22% by number) and squids (11% by number). Heteropods and tunicates made up 4% by number of the diet. Small fish; squid; Auxis thazard; a pelagic crab, Pleuroncodes planipes; and sierra mackerel, Scombero- morus sierra, have been found in the stomachs of E. lin- eatus (Calkins and Klawe 1963). Table 17 presents examples of food items found in stomachs of Euthynnus from various areas. It can be seen in Table 17 that Postel (1954) listed E. alletteratus, pre- sumably a juvenile, from the stomach of an adult E. al- letteratus. 3.43 Growth rate Euthynnus affinis The available information on the age and growth of E. affinis is sketchy and fragmentary. No data are avail- able on the growth of the larvae. On the juveniles, Kish- inouye (1923) suggested that a 115 mm specimen caught off Port Keelung in August may have been about 3 mo old. Wade (1950a) speculated that a 115 mm long speci- men from the Celebes Sea was 3 or 4 mo old, and that a 175 mm specimen may have been spawned as long as 6 Table 17. — Food of Euthynnus spp. Number of food Percentage Percentage Food items organisms prevalence by volume Food of Euthynnus affinis. (From Kumaran 1964, table 1.) Crustacea: (20.4) (5.2) Isopods 7 2.8 — Amphipods 9 2.8 — Cope pods 9 3.4 0.1 Penaeus sp. 3 1.4 0.1 Phyllosoma larvae 6 2.7 0.1 Megalopa larvae 8 2.0 0.1 Squilla sp. 2 0.7 — Alima larvae 82 5.5 3.4 Unidentified crustaceans 17 5.5 1.1 Gastropoda: Pteropods 5 1.4 — Cephalopoda: (12.3) (56.5) Sepwteuthis sp. 25 10.9 55.7 Loligo sp. 2 1.4 0.8 Vertebrata (Pisces): (87.1) (38.3) Sardinella spp. 10 5.5 0.7 Stolephorus commersonii 15 6.8 1.0 Anchoviella tri 56 23.7 3.4 Other clupeids 6 3.4 0.5 Saurida sp. 4 2.0 0.4 Leptocephalus 3 1.4 0.1 Hemiramphus sp. 1 0.7 — Holocentrus sp. 3 1.4 0.6 Sphyraena sp. 5 2.7 — SUlago sihama 7 4.1 0.4 Lactarius lactarius 1 0.7 0.1 Carangids 18 5.5 13.8 Leiognathus spp. 141 32.5 6.8 Sciaena sp. 1 0.7 — Euthynnus affinis 1 0.7 — Triacanthus sp. 1 0.7 0.2 Unidentified fish including larvae 36 14.9 9.5 Food of Euthynnus alletteratus. (From Postel 1954, table 1.) Fish: Sardinella aurita Smaris sp. Sardinella sp. Ammodytes sp. Engraulis sp. Galeiodes polydactylus Aulopus sp. Scomber japonicus Saurida parri Auxis sp. Myctophum sp. Euthynnus alletteratus Fodiator acutus Caranx Rhoncus Cypselurus sp. Decapterus pundtatus Hemiramphidae Vomer Setipinnis Sphyraena sp. Pagellus sp. Box boops Sargus sp. Molluscs: Shelled (?) molluscs Sepia sp. Loligo sp. Allotenthis africana Crustacea: Planktonic Crustacea Euphausiaceae Sergestidae Parapeneus longirostris Bryozoans Madreporaires Green algae mo before its capture. These observations suggest a growth rate of 1.0 to 1.3 mm/day. Yabe et al. (1953) presented length data of preadult E. affinis landed at the port of Aburatsu, Japan, during 36 August- October 1950 (Table 18; Fig. 18). Yabe et al. indicated that E. affinis between 150 and 250 mm were in their first year of life. Figure 18 suggests an average growth rate of 1.5 mm/day. This growth rate is not very different from that suggested for E. affinis juveniles in the Philippines. Ommanney (1953) observed the age-size relationship of E. affinis caught near the Seychelles. Although the basis for determining the age-size relationship is not made clear, he suggested that postlarval to 25 cm fish Table 18. — Average size of Euthynnus affinis landed at Aburatsu, Japan. (From Yabe et al. 1953, table 5.) No. of fish Fork length (mm) Month measured Range Mean Aug. 26 107 183-240 200 30 51 201-225 213 31 98 203-239 217 Sept. 1 53 194-240 214 2 19 199-268 218 4 92 209-245 225 5 78 204-290 224 6 91 200-309 221 7 79 203-307 235 8 132 196-325 234 9 149 200-271 222 20 115 213-274 236 25 13 223-255 236 Oct. 6 5 230-295 241 11 9 252-278 262 13 24 254-286 265 16 138 244-313 270 17 111 220-332 272 AUG. SEPT. OCT. were in their first year of life, 25 to 45 cm fish in their sec- ond year, 45 to 65 cm fish in their third year, and 65 cm and larger fish in their fourth year and over. Landau (1965) determined the ages of E. affinis from the southern Red Sea based on the annular marks on the vertebral centra. The age-size relationships are given in Table 19. Landau, using the graphical method, esti- mated that the L, for E. affinis in the Red Sea was 580 mm SL. Table 19. — Age-size relationships of Euthynnus affinis from the Red Sea. (From Landau 1965, tables 2, 3.) No. of Length (SL) 1 in mm Approximate mean Age fish Range Mean w eight (kg) Southern Red Sea (April-June 1964) I 28 310-430 345 0.9 11 11 370-520 456 2.1 III 18 470-560 511 2.8 IV 25 520-590 544 3.3 V 1(1 520-600 554 3.5 Bay of Eilat, Red Sea (May 1964) I 78 320-340 370 1.0 II 2 505 and 525 — 3.0 'SL is standard length defined by the author as the distance from the snout to the insertion of the caudal fin. On the basis of annular marks on the first dorsal spine of E. affinis, Shabotinets (1968) determined the age-size relationship of fish taken in the Gulf of Aden as shown below. ige Size (cm) 3 50-65 4 55-75 5 65-80 6 86 Figure 18.— Growth of preadult Euthynnus affinis off the southern coast of Japan. (Data from Yabe et al. 1953.) Euthynnus alletteratus Houde and Richards (1969) observed the growth of lar- val E. alletteratus under laboratory conditions. They col- lected fertilized eggs in the western edge of the Gulf Stream near Miami, Fla., and incubated and hatched the eggs in 20- and 140-gal (75.5- and 530-liter) aquaria. The growth in length of the larvae in one of their rearing experiments is shown in Figure 19. As can be seen the lar- val fish grew from approximately 2.5 mm to a little less than 8.5 mm in 18 days. Houde and Richards noted that the growth of the larvae was probably not as fast as in the natural environment. Based on modal groups in length-frequency distribu- tions Postel (1955b) presented the following age-length relationships for E. alletteratus off Dakar in the eastern Atlantic- Less than 1 yr (Group 0) <30 cm lto2yr(Groupl) 30-45 cm 2 to 3 yr (Group 2) 45-60 cm 3 to 4 yr (Group 3) 60-75 cm Over4yr >75cm 37 7 o o o o 8 Table 20.— Age-length and age-weight relation- ships for Euthynnus alletteratus in the Mediterra- nean Sea. (From Landau 1965, table 1.) 2 4 6 8 10 12 14 16 18 20 DAYS AFTER HATCHING Figure 19. — Growth in length of Euthynnus alletteratus larvae oreared in the laboratory. (From Houde and Richards 1969, fig. 3.) Landau (1965) determined the ages of E. alletteratus in the Mediterranean Sea by reading marks on the verte- bral centra. Lengths of fish at various ages were back- calculated by relating the radius of annular marks on the vertebrae to the length by the regression: LS = 45.85V + 72.62 where LS is standard length defined as distance from snout to insertion of caudal fin, and Vis vertebral radius. The age-size relations determined by Landau are given in Table 20. Landau also estimated L x for E. alletteratus as 840 mm, using the graphical method on size obtained by back-calculations. Euthynnus lineatus Except for some observations on the growth of juve- nile E. lineatus there is nothing in the literature on the growth of this species. Clemens (1956) was able to rear juvenile E. lineatus for up to 10 days in shipboard aquaria. From the beginning of the holding experiment to the end 10 days later, the average weight of the juve- niles increased 11 times and the average length in- creased approximately 1.4 times (Table 21). Length (SL)' in mm Approximate mean Age Range Mean weight (kg) I 28-49 358.4 0.8 II 46-68 539.1 2.8 in 54-75 637.2 4.5 IV 61-79 701.9 6.0 V 65-84 755.0 7.5 VI 74-86 801.5 8.5 VII 75-84 810 9.0 SL is standard length defined by the author as the distance from the snout to the insertion of the caudal fin. 3.44 Metabolism Malvin and Vander (1967) determined the plasma renin activity in E. affinis. They pointed out that there is general agreement that freshwater fishes contain renin in their kidneys but that this problem had not been re- solved in marine fishes; furthermore, plasma renin had not been measured for marine species. Their results showed that certain characteristics in the plasma renin activity of E. affinis and K. pelamis were identical to that of the mammalian renin-angiotensin system which strongly indicated to them that the material being evalu- ated was angiotensin generated by the enzymatic action of renin. It was determined that the renin activity, ex- pressed as angiotensin-equivalents, was 23.3 and 15.8 ng/ml of plasma for two specimens of E. affinis. Klawe et al. (1963) determined the hemoglobin con- tent of the blood of E. lineatus. They noted that the hemoglobin content of the blood of fishes is generally re- lated to the level of activity of the species. The hemo- globin concentration of E. lineatus blood ranged from 16.9 to 19.9 g/100 ml for five fish measuring 427 to 657 mm. This level of hemoglobin concentration was higher than for Scomber japonicus and Sarda chiliensis. They speculated that the higher hemoglobin content of the blood of E. lineatus was somehow related to its complex cutaneous vascular system which S. japonicus and S. chiliensis lack. 3.5 Behavior For feeding behavior, see section 3.4; for reproductive behavior, see section 3.13. Table 21. — Growth of postlarval Euthynnus lineatus. (From Clemens 1956, table 1.) Number of fish Hours 1 Standard length (mm) Range Average Fork length (mm) Range Average Weight (g) Range Average Range Average 23 3 3 4 171-175 194-200 244-248 173 197 246 17.0-37.5 48.0-52.0 54.0-55.0 59.0-71.5 26.8 49.3 54.3 63.6 18.5-40.0 51.0-55.0 58.0 63.0-75.0 28.3 52.0 58.0 67.5 0.10-0.57 0.29 1.51-1.91 1.70 1.94-2.37 2.14 2.61-4.72 3.46 Hours of growth computed from time fish started feeding, 42 h after capture. 38 3.51 Migrations and local movements See section 5.3. 3.52 Schooling Aspects of the schooling behavior of Euthynnus rela- tive to feeding have been discussed in section 3.41. Other observations on the schooling behavior of Euthynnus indicate that these species tend to school with other spe- cies. In the Indian Ocean off the east African coast, E. af- finis were found in schools with small T. albacares, K. pelamis, Auxis sp., and a carangid, Megalaspis cordyla (Williams 1963). Williams noted, however, that all indi- viduals in the schools were of much the same size. He also found that with small E. affinis "the schooling is strong and disciplined." Elsewhere in the Indian Ocean, Williams (1963) noted that in waters around Sri Lanka, mixed schools of Auxis spp. and E. affinis are common. Sivasubramaniam (1970) stated that K. pelamis, Auxis spp., and young T. albacares occur together with E. affinis and that the catches are almost always mixed. Fourmanoir (1957) observed that around Madagascar, schools of E. affinis were almost always distinct from that of other species of tuna, except in June to the east of Nosy-Be, where T. albacares were taken at the same time as E. affinis. Williams (1963) noted that in east Africa, schools of E. affinis were composed of 100 to 1,000 or more individ- uals, and in Sri Lanka as many as 5,000 individuals (mixed E. affinis and Auxis spp.) may be taken in one haul of a beach seine. Cahn (1972) investigated side-to-side spacing and positional orientation of E. affinis during schooling in experimental tanks. The study was designed to demon- strate the role of the lateral line sensory system in the schooling of E. affinis. Euthynnus affinis, in the experi- mental tanks, significantly increased their side-to-side spacing and altered their diagonal to abeam position ratios so that the abeam orientation assumed increased importance when the hydrodynamic field between ori- enting fish was blocked by a transparent partition. She concluded that hydrodynamic contact is essential for the typical spacing and positional orientation in schooling, and that the lateral line plays a prime regulatory role as the water turbulence detector. Although E. alletteratus are found in schools most of the time, they have a tendency to scatter during certain periods of the year (Marchal 1963). Marchal further noted that E. alletteratus schools have an elliptical shape of variable size and may be as long as 30 m along the long axis. Like E. affinis, E. alletteratus often school with other species, including Auxis sp., Sarda sarda, and Selar crumenophthalmus. All the individuals in these mixed schools tend to be of the same size (Marchal 1963). Euthynnus lineatus in Peruvian waters are frequently found in schools with T. albacares and K. pelamis of the same size (Bini 1952). The number of individuals in the school, however, was not as great as the commercially important species. Calkins and Klawe (1963) reported that commercial tuna fishermen have observed that E. lineatus will frequently collect around drifting or anchored tuna boats. They noted that T. albacares and K. pelamis also exhibit this type of behavior but be- lieved this behavior pattern was more pronounced with E. lineatus. Hunter and Mitchell (1967) observed schools of E. lineatus beneath flotsam or drifting objects. How- ever, these schools remained near the floating objects only for short periods and they did not swim as close to the objects as did other small fishes. They could not ascertain whether the schools of E. lineatus were truly as- sociated with a particular object. 3.53 Responses to stimuli Tester (1959) summarized the various experiments on the response of E. affinis and other tunas to stimuli (Hsiao 1952; Miyake 1952; Tester 1952a, 1952b; Van Weel 1952; Tester et al. 1954; Hsiao and Tester 1955; Tester et al. 1955; Miyake and Steiger 1957). It was found that E. affinis were attracted to continuous white light over a range of moderate intensity (about 70 to 450 fc). Euthynnus affinis were not attracted to a light of weaker intensity, and were repelled by a light of stronger intensity (Hsiao 1952). In experiments testing the re- action of E. affinis to moving objects of various colors, it was found that white lures were slightly more attractive than red, black, or silver (Hsiao and Tester 1955). Hsiao and Tester (1955) noted, however, that this may have been associated with greater visibility than color prefer- ence. Experiments on the chemoreception of E. affinis indicated that this species had a well-developed sense of smell or taste in that they were strongly attracted to clear colorless extracts of tuna flesh. It was further found that the attractant was contained in the protein rather than the fat fraction of the clear extract (Van Weel 1952; Tester et al. 1955). It was also determined that E. affinis became conditioned to the smell of juices exuded from the food which presumably contained common or simi- lar substances which stimulated the feeding response (Tester et al. 1954). Nakamura (1968) determined the visual acuity of E. affinis. Visual acuity was defined as the ability to see clearly the fine details of objects, especially as the objects become smaller and closer together. To determine the visual acuity, E. affinis were trained to discriminate be- tween vertically and horizontally striped images that were projected on an opal glass plate in an experimental tank. The visual acuity of two E. affinis, 36.4 cm (0.9 kg) and 43.4 cm (1.6 kg), were determined at various levels of luminance (Fig. 20). Nakamura (1968) also conducted these experiments on K. pelamis and noted that at lower luminances the visual acuity of the two species were similar. At higher luminances, however, K. pelamis had a greater visual acuity than E. affinis. Experiments have also been conducted to describe the hearing thresholds and frequencies audible to E. affinis (Iversen 1969). Based on experiments with two speci- mens, Iversen determined a threshold curve for acoustic sound pressure for E. affinis which showed that the fish perceived sounds from 100 to 1,100 Hz (Fig. 21). The 39 06 -2.5 -2.0 -1.5 -10 -0.5 +0.5 +1.0 +1.5 LOG OF LUMINANCE OF WHITE STRIPES ( FOOT- LAMBERTS) 30- 20 -10 I - L \ t I 1 A i 44 cm Euthynnus affinis o 54 cm Euthynnus of finis i 1 1 H < i 100 200 1000 300 400 500 FREQUENCY (Hz) Figure 21.— Acoustic sound pressure thresholds of two Euthynnus affinis. (From Iversen 1969, fig. 1.) Figure 20. — Visual acuity curve of Euthynnus affinis at adaptive illumination of 170 luxes. Curve fitted by eye. (From Nakamura 1968, fig. 3.) (Although not explicitly stated, it is believed that visual acuity is plotted against log, of luminance.) lowest mean threshold was 7 dB/mbar at 500 Hz. At 100 Hz the threshold was 30 dB/mbar higher than at 500 Hz, and at 1,100 Hz it was 23 dB/mbar higher. The mean thresholds for E. affinis were consistently higher than those for T. albacares (Iversen 1967). Iversen (1969) noted that this difference could have resulted in part from the lack of a gas bladder in E. affinis. Steffel et al. (1976) conducted experiments on captive E. affinis to determine their ability to discriminate temperature gradients. Tests on two fish yielded a dis- crimination threshold of 0.10° to 0.15°C. Their experi- ments indicated that the thermal sensitivity of E. affinis is no more acute than that of inshore fishes and appeared inadequate for direct sensing of weak horizontal temper- ature gradients at sea. Walters (1966) determined the swimming speed of E. affinis by high-speed motion pictures. He observed that E. affinis traveled an average of 5.9 body lengths/s while feeding and a maximum of 10.0 body lengths/s. The non- feeding swimming speed, with food present, averaged 4.5 body lengths/s and ranged from 2.9 to 12.5 body lengths/s. Magnuson (1969) investigated the swimming activity of captive E. affinis as related to their search for food in outdoor tanks. He determined that the average swim- ming speed of E. affinis, averaging about 35 cm long, was 80 cm/s during the day and 83 cm/s at night in tanks con- taining no food. These fish had been in captivity for less than a month. Swimming speed measurements made after the fish had been in captivity for 5 to 6 and 8 mo showed that the speed was lower than that of fish held less than a month, but no marked difference was observed between the mean speed during the day (74 cm/s) and the mean speed during the night (72 cm/s). Magnuson (1969) also measured the swimming speed of E. affinis in tanks containing several thousand live prey fish. They appeared to swim faster than those without food, averaging 108 cm/s during the day and 92 cm/s at night. He noted that the higher day speeds were caused from intermittent high-speed pursuit of the prey. Euthynnus affinis did not prey on the baitfish at night. Magnuson (1969) found that swimming speed was highest after a meal and decreased when the fish were de- prived of food. He argued that if the level of swimming activity is regulated by search for food, swimming speed should be higher when motivation to feed is increased by deprivation of food. Because swimming speed decreased during deprivation, he concluded that swimming activity must be regulated in response to some biological need other than food search. He further concluded that swim- ming activity appeared to be more closely related to the requirements for maintaining hydrostatic equilibrium and gill ventilation, than for food search. Inoue et al. (1970) also made observations on the swim- ming speed of E. affinis. They found that E. affinis swam at a speed of 0.30-1.27 m/s during the day and 0.33-0.75 m/s under artificial lights in their experimental tanks 4 m in diameter and 0.6 m deep. Nakamura and Magnuson (1965) gave a detailed description of the coloration of living E. affinis. In addi- tion to the permanent coloration, E. affinis exhibited three transient color patterns or markings that were re- lated to feeding. These patterns or markings were black spots ventral to the pectoral fins, faint vertical bars on the flanks, and a yellowish middorsal stripe. These three color patterns were observed when E. affinis were feeding. Nakamura and Magnuson (1965) suggested that these transient color patterns may act as "social re- leasers" to signal the presence of food to other members of the school. Wickham et al. (1973) investigated the efficacy of midwater artificial structures for attracting pelagic sport fishes in the Gulf of Mexico near Panama City, Fla. With 40 equal experimental fishing effort they obtained signifi- cantly greater catches of E. alletteraius around the arti- ficial structures than in adjacent control areas. How- ever, they noted that E. alletteratus were seldom observed or captured at the structures unless baitfish were present. They concluded that E. alletteratus appar- ently were not attracted by the structures per se, but rather by the presence of the baitfishes that were at- tracted to the structures. 4 POPULATION 4.1 Structure 4.11 Sex ratio 70 TROLL N = I850 DRIFT NET (4 -6 MESH) N = 740 16.1 24.1 32.1 40.1 48.1 56.1 64.1 20 28 36 44 52 FORK LENGTH (cm) 60 68 The sex ratios of E. affinis in various localities are given in Table 22. Williamson (1970) estimated the sex ratio of E. affinis by size near Hong Kong. He found that for fish from 38 to 49 cm the sexes appeared to be repre- sented in equal numbers but for fish from 50 to 73 cm, 67% of the fish were males. The sex ratio of E. alletteratus in various localities is given in Table 23. No information is available on the sex ratio of E. lineatus. Table 22. — Sex ratio of Euthynnus affinis. Locality Number (percent) Sample size Males Females Source East Africa (western 11 Indian Ocean) East Africa (western 37 Indian Ocean) Hawaii 93 6(54.5) 5(45.4) Morrow (1954) 22(59.4) 15(40.5) Williams (1964) Philippines 45(48.4) 48(51.6) Tester and Nakamura(1957) 456 243(53.3) 213(46.7) Wade (1950b) Table 23. — Sex ratio of Euthynnus alletteratus. Locality Number (percent) Sample size Males Females Source Between North Carolina 227 121(53.3) 106(46.7) deSylvaand and northern Florida Rathjen (1961) Miami, Fla. 550 261(47.5) 289(52.5) deSylvaand Rathjen (1961) Barbate and Tarifa, 378 198(52.4) 180(47.6) Rodriguez-Roda Spain (1966) Senegal 866 432(49.9) 434(50.1) Postel (1955b) 4.12 Age composition See section 4.13. 4.13 Size composition Euthynnus affinis The length-frequency distribution of E. affinis caught by trolling and drift nets in the southwest region of the Sri Lanka fishery is shown in Figure 22. The E. affinis Figure 22. — Length frequencies of Euthynnus affinis caught by drift nets and troll lines in the southwest regions of Sri Lanka. (From Sivasubramaniam 1970, fig. 3.) taken by the commercial fishery ranges from 20 to 65 cm. Occasionally fish in the 15 to 20 cm and 65 to 68 cm groups are also taken (Sivasubramaniam 1970). Sivasu- bramaniam discussed the size selectivity of the various gear used in the Sri Lanka fishery. He noted that the trolling gear sampled a wide range of sizes of E. affinis. However, he also stated that trolling gear selected a larger proportion of smaller sizes of fish in the stock. Although drift nets are highly selective, the use of a wider range of mesh sizes from 10.2 to 15.2 cm (4-6 in) in Sri Lanka made these nets less selective. He indicated that the use of 10.2 to 15.2 cm mesh nets resulted in the cap- ture of a fairly wide size range of E. affinis. Since the pole-and-line fishing method is directed primarily at K. pelamis which range from 40 to 55 cm, this fishing method tends to select E. affinis of the same size range which are found together with K. pelamis. Finally, Si- vasubramaniam (1970) pointed out that the selectivity of longline gear relative to the size and behavior of E. affinis eliminated this species from longline catches. It appears that in general all the various life stages of E. affinis oc- cupy the same habitat, and the size of fish taken is pri- marily dictated by the gear used. This probably holds true for the other two species of Euthynnus which are also coastal fishes. The length -frequency distribution of E. affinis caught by trolling along the southeast coast of India is shown in Figure 23. The E. affinis caught during July 1960 in this area ranged from about 42 to 68 cm. No modes were dis- cernible in the length distribution. The August 1961 sam- ple showed a mode at around 46 cm and the September 1961 sample at around 52 cm. As noted earlier, other fishing gear in addition to trolling gear are used to catch E. affinis along the southeast coast of India. Presumably, the length-frequency distribution of E. affinis caught by other gear would differ from that of fish caught by trolling. The length range of E. affinis caught along the south- west coast of India is given by Bennet (1964) (Table 24). The gear used in this fishery includes drift nets and hook and line (presumably trolling gear). Shore seines are oc- 41 JULY I960(N° 15) 1 1 - I 35 AUG. 1961 (N« 32) ' ' i II 30 25 20 15 - 10 - 5 n "1 1 1 1 1 II 1 ; , l SEPT. 1961 (N- 16) 1 - 15 10 5 400 500 600 700 TOTAL LENGTH (mm) Figure 23. — Length frequencies of Euthynnus affinis caught by trolling off the southeast coast of India. (From Silas 1967b, fig. 15.) Table 24.- -Size composition of Euthynnus affinis from the southwest coast of India. (From Bennet 1965 table 3.) Minimum Maximum Minimum Maximum length length length length Month (cm) (cm) Month (cm) (cm) 1960 1961 July 45.0 60.5 January 30.5 62.8 August 43.5 64.0 February 31.7 58.5 September 43.0 60.0 March 24.3 62.3 October 15.0 62.3 April 30.1 70.1 November 24.7 55.0 May 42.5 67.3 December 26.3 62.7 June 42.5 63.7 July 48.2 66.1 August 41.6 67.3 September 42.2 61.0 October 20.3 59.0 casionally used. The fish caught during the sampling pe- riod measured from 15 to 70 cm. Bennet (1964) noted that the smallest fish were taken in October 1960 by shore seine. He further stated that the smaller sizes are not represented in the commercial catches. The size range and the modal groups of E. affinis caught in vari- ous other localities in the Indian Ocean as summarized by Williams (1963) are shown in Table 25. Length -frequency data on E. affinis caught in Japanese waters are scanty. Yabe et al. (1953) presented size data on young E. affinis landed at Aburatsu, Kyu- shu, Japan, in 1950 (Fig. 24). During a fishing and marketing experiment (see sec- tion 5), E. affinis measuring 23 to 73 cm were taken by a Table 25. — Size composition of catches of Euthynns affinis in vari- ous areas of the Indian Ocean. (From Williams 1963, table 3.) Area and author Main size groups Overall size Australia Roughley(1951) 2.2-4.1 kg 5.4-6.6 kg East Africa Morrow (1954) — Williams (1964) 1.0-2.2 kg 3.6-5.4 kg Madagascar Fourmanoir (1955) — Seychelles Ommanney (1953) 45-65 cm Over 65 cm Somalia Ogilvieet al. (1954) 50 cm at 3-4 Up to 76 cm and 8.2 kg 51-71 cm at 1.9-5.2 kg 40-78 cm at 1.0-7.3 kg Up to 80 cm 43-87 cm at 1.0-8.6 kg 50 cm at 3-4 kg Up to 79 cm and 6 kg jf AUG. 26 1m n-, AUG. 30 rf-rfk_ AUG. 31 _xrfhrrh __ SEPT. 1 >■ o 2 Ul nltih SEPT. 2 1 3 O Ul K b. H ^rnrm ! SEPT. 3 Z HI o £C Ul 0. ■n. SEPT. 5 | _rriTi-ru _ SEPT. 6 -r-rrm-ri- 1 SEPT. 7 ) _jtJTTu SEPT. 8 ^-rTTTl~h-^_ SEPT. 9 _riTrfk SEPT. 20 200 I 205 250 I 255 LENGTH (mm) 300 I 305 Figure 24.— Length frequencies of Euthynnus affinis landed at Aburatsu, Kyushu, Japan, in 1950. (From Yabe et al. 1953, fig. 1.) 42 modified purse seiner off Hong Kong. Two size groups were represented in the landings. The dominant group included fish from 50 to 73 cm long (2.5-7.0 kg) and the other less numerous group was composed of fish 38 to 44 cm long (1.2-2.5 kg) (Williamson 1970). In the Philippines, the size of E. affinis taken by troll- ing by research vessels is shown in Figure 25. The fish ranged from about 30 to 80 cm and the length-frequency distribution showed a prominent mode at about 50 cm. Other commercial fishing methods capture much smaller E. affinis. Wade (1950a) reported finding E. affinis as 45 35 20 5 S.F. BAIRD 8 T.N.GILL 300 400 500 600 700 800 TOTAL LENGTH (mm) Figure 25. — Length frequency of Euthynnus affinis taken by trolling in Philippine waters, 1947-49. (From Ronquillo 1963, fig. 16.) small as 40 mm in the fish markets in the Philippines. The length-frequency distribution of E. affinis taken in recent purse seine surveys near the Philippines (Rosen- berg and Simpson 6 ) is given below. Length (cm) 30 35 40 45 50 Elsewhere in the Pacific, size distribution of E. affinis taken by trolling around Hawaii and the Marquesas is shown in Figures 26 and 27, respectively. Length-weight relationships have been determined for E. affinis from various locations in the Indo-Pacific (Table 26). Number Percent 1 0.3 79 25.2 228 72.6 6 1.9 ''Rosenberg, K. J., and A. C. Simpson. 1975. Pelagic fisheries development - trip reports chartered purse seine vessels. Regional. 9 February 1975 to 26 March 1975, voyage 3, 28 p. South China Sea Fisher- ies Development and Coordinating Programme. 4 — MAY H JUNE JULY J I ■ I 1 I I — » AUGUST SEPTEMBER OCTOBER _l l__„i_ NOVEMBER _Q I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 WEIGHT (POUNDS) 0.4 1 0.9 I 1.4 1 1.8 1 2.21 2.7 I 3.2 1 3.6 I 4.1 I 4.5 I 5.01 5.4! 5.7 1 6.3 16.8 I WEIGHT (kg) Figure 26. — Weight composition of Euthynnus affinis captured off Kaneohe, Oahu, Hawaii, by months, 1951-55. (From Tester and Nakamura 1957, fig. 6.) i — i — i — i — r 50 I 51 I 61 LENGTH (cm) 70 HO I 81 Figure 27. — Length frequency of Euthynnus affinis taken by troll- ing around the Marquesas Islands. (Data from files of Southwest Fisheries Center, National Marine Fisheries Service, NOAA. Honolulu, HI 96812.) 43 Table 26. — Length-weight relations W = aL of Euthynnus. Predictive equations were fit throught logarithmic trans- formation of data (see Ricker 1973). Species and locality No. of fish Size range offish Weight Fork length a b 1.81-5.22 kg 52-71 cm 0.0166 2.963 (4-11.5 lb) — 12-58 cm 0.0137 3.0249 - - 0.0138 3.0287 - - 0.08853 2.5649 0.45-6.80 kg 0.0108 3.1544 (1-15 lb) — 34.4-81 .0 cm 0.0334 2.83768 - 33.1-65.2 cm 0.0211 2.94854 - - 0.0222 2.914897 - - 0.0152 3.0 1.35-13.9 kg 473-1,015 mm 0.0163 3.0 0.23-8.39 kg 23.1-85.8 cm 0.00496 3.26314 0.91-6.26 kg 365-667 mm 0.01327 3.0817 (2-13 lb 13 oz) Weight Length unit unit Source E af finis 10 (Indian Ocean) E. affinis 201 (Indian Ocean) E. affinis (Indian Ocean) E. affinis 226 (South China Sea) E. affinis 101 (Hawaii) E. affinis (males) 203 (Philippines) E. affinis (females) 165 (Philippines) E. alletteratus 325 (western Mediterranean) E. alletteratus (eastern Atlantic) E. alletteratus 100 (Tunisia) E. alletteratus 343 (Florida) E. lineatus 109 (eastern Pacific) cm Morrow (1954) cm Sivasubramaniam (1966) cm Silas (1967b) cm Williamson (1970) cm Tester and Naka- mura (1957) cm Ronquillo (1963) cm Ronquillo (1963) cm Rodriguez- Roda(1966) cm Postel(1950) cm Postel (1956) cm Beardsley and Richards (1970) cm Klawe and Calkins (1965) Euthynnus alletteratus Juvenile E. alletteratus caught in the Sea of Marmara (from last week in August to mid-September) and the Dardanelles (mid-August to first week in October) in 1959 apparently were the first records of juveniles in Turkish waters (Demir 1963). The juveniles caught in the Sea of Marmara were slightly smaller (mode at 20 cm) than those taken in the Dardanelles (mode at 23 cm) (Fig. 28). Rodriguez-Roda (1966) presented length-frequency distributions of E. alletteratus landed at Barbate and Tarifa, Spain, in 1963 and 1964 (Fig. 29). He smoothed the percentage frequency of the various length classes by /n-i +2/„ +/ n+ , the formula, / The length distribu- tions of the males and females were the same for both years. However, the length-frequency distribution in 1963 showed a single strong mode at 60 cm whereas the 1964 distribution showed two strong modes at 45 and 60 cm and a lesser mode at about 85 cm. It is of interest that the weight-frequency distribution, also smoothed by the formula given above, showed a single prominent mode at 4 kg in 1963 but in 1964 showed a mode at about 2 kg and another at about 9 kg (Fig. 30). Thus, in 1963 both the length- and weight-frequency distributions indicated only a single size group in the fishery but in 1964, three size groups were represented in the landings in terms of length, and only two size groups in terms of weight. Postel (1955b) presented the length-frequency distri- bution of E. alletteratus taken in the eastern Atlantic off Senegal (Fig. 31). He stated that the length group from 30 to 45 cm were 1 to 2 yr old fish and those from 60 to 75 DARDANELLES 15 16 17 18 19 20 21 22 23 24 25 26 LENGTH (cm) Figure 28.— Length frequencies of juvenile Euthynnus alletteratus from the Sea of Marmara and the Dardanelles. (From Demir 1963, fig. 2.) 44 40 1963 MALES(N-=9I) FEMALES (N = 74) MALES(N = I07) FEMALES(N = I06) 60 70 LENGTH (cm) Figure 29. — Length frequencies of Euthynnus alletteratus landed at Barbate and Tarifa, Spain, in 1963 and 1964. (From Rodnguez- Roda 1966, fig. 6.) 30 i 1 1 / \ 1963 1 1 1 1 1 /\ / \ / \ 1964 \ / / \ / \ / / \ \ / / \ \ / / / / \ \ \ \ / / \ \ / / \ \ / / \ \ \ / J _^ --^_ L_ 1 2 3 4 5 6 7 8 9 10 II 12 13 WEIGHT (kg) Figure 30. — Weight frequencies of Euthynnus alletteratus landed at Barbate and Tarifa, Spain, in 1963 and 1964. (From Rodnguez- Roda 1966, fig. 7.) cm were 3 to 4 yr old. He noted that fish 45 to 60 cm long (2-3 yr old) were not found in the area off Cap Vert, Sene- gal. However, Marchal (1963) stated that E. alletteratus from 50 to 70 cm were found in normal proportions off the coast of Guinea. The length-frequency distribution of E. alletteratus caught by sport fishermen on charter boats off Miami, Fla., is shown in Figure 32. In Figure 33 is shown the length-frequency distribution of E. alletteratus taken by commercial trolling between North Carolina and north- ern Florida. The length range offish generally landed by the Miami sport fishery (Fig. 32) was from about 500 to 750 mm (de Sylva and Rathjen 1961). de Sylva and Rath- jen noted that only a very few large or very small fish were taken and that fish larger than 620 mm were pre- 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 I I I I I I I I I I I I I I I 24 29 34 39 44 49 54 59 64 69 74 79 84 89 94 LENGTH (cm) Figure 31. — Length frequency of Euthynnus alletteratus from Senegal. (Data from Postel 1955b.) u. 20 !| 15 3 420 500 580 660 FORK LENGTH (mm) 740 H,". , Figure 32. — Length frequencies of male and female Euthynnus alletteratus caught by anglers off Miami, Fla., September 1952 to August 1953. (From de Sylva and Rathjen 1961, fig. 1.) dominantly males, possibly suggesting either a differ- ential growth rate or mortality beginning at that size be- tween the sexes. They also found that the E. alletteratus taken by commercial trolling between North Carolina and northern Florida were of similar size as those taken off Miami. However, they pointed out that the length- frequency distribution of the Miami sample showed a more even distribution of sizes while that of North Carolina-northern Florida was markedly leptokurtic. They suggested several causes for the disparity in the length-frequency distributions from the two areas, in- cluding the fact that the commercial trolling gear pos- sibly selected a certain size range of fish by the use of only a certain range of hook sizes, as also suggested by Carlson (1952). Carlson indicated that the selectivity was possibly due to the loss of smaller fish caused by the hooks pulling free more easily, de Sylva and Rathjen 45 300 400 500 600 700 800 900 FORK LENGTH (mm) Figure 33. — Length frequency of 217 Euthynnus alletteratus caught by commercial trolling gear between North Carolina and northern Florida, July 1951. (From de Sylva and Rathjen 1961, fig. 2.) (1961) also suggested that in the Miami sport fishery the anglers use a wider assortment of baits and artificial lures and because the angler is more careful in landing the fish, the hook is less apt to pull free. Beardsley and Richards (1970) also presented length- frequency data of E. alletteratus caught in the sport fish- ery in southern Florida (Fig. 34). These fish were sampled at a Florida taxidermy firm during a period from September 1967 to September 1968. They indi- cated that because the fish was sampled at a taxidermy company the length-frequency distribution may be biased because usually only the largest fish caught are preserved and mounted. A comparison of the length- frequency data presented by de Sylva and Rathjen (1961) (Fig. 32) with that of Beardsley and Richards (1970) (Fig. 34), however, does not clearly indicate that larger fish were being selected. The length-weight relationships determined for E. al- letteratus from various localities are given in Table 26. Euthynnus lineatus The length-frequency distribution of E. lineatus taken between June 1972 and August 1975 in the Gulf of Cali- fornia and from Baja California to Ecuador is shown in Figure 35. The length-weight relationship for E. lineatus com- puted by Klawe and Calkins (1965) is given in Table 26. The largest E. lineatus collected by Calkins and Klawe was a male 636 mm long which weighed 4.8 kg (10.5 lb). 4.14 Subpopulations For various reasons, probably including the fact that 1) Euthynnus in general are commercially not very impor- o CC LlJ , oo 5 2 20 ^^rfnti XI Q MA JZL OCT.- DEC. (N=59) tk n cm JAN.- MAR. (N = I05) APR- JUNE (N=33) n JULY -SEPT. (N = I48) xEL n_ 20 30 I I 21 31 40 I 41 50 I 51 60 I 61 70 I 71 90 I 91 FORK LENGTH (cm) Figure 34.— Length frequencies by quarters of the year for Euthyn- nus alletteratus sampled from a taxidermy plant in south Florida from September 1967 through September 1968. (From Beardsley and Richards 1970, fig. 2.) _ - p. - 6 - - 4 - - 2 ~ lr -, ^ It-Mil i-TH ■mum... 30 35 40 45 50 55 60 65 LENGTH (cm) Figure 35.— Length frequency of Euthynnus lineatus. (Data courtesy of W. Klawe, Inter-Am. Trop. Tuna Coram., La Jolla, Calif.) tant and 2) investigators had been concerned primarily with clarifying the species status in the genus, very little has been done to investigate the subpopulation problem within this group. Based on various published works on 46 meristic and morphometric characters of E. alletteratus in the Mediterranean and eastern Atlantic, Marchal (1963) concluded that two subpopulations existed in this area. He stated that the Senegal population extended at least from Cap Vert, Senegal, to Ghana and probably well beyond the tropical coast of west Africa. The Medi- terranean subpopulation, which can be differentiated from the subpopulation off Senegal by meristic and mor- phometric characters, extends into the Atlantic south to Morocco and perhaps to as far north as the Bay of Biscay, France. In an earlier work Postel (1953) attempted to de- termine if the E. alletteratus that appeared in the cold season and the warm season off Cap Vert belonged to separate subpopulations on the basis of the number of spots on the pectoral region of the two groups offish. Be- cause of the wide variability of the number of spots the results were not conclusive. In a preliminary study of the serology of tunas in- cluding E. affinis, Cushing (1956) indicated that it was probable that serological techniques could be applied profitably to the study of racial and specific variation in tunas. He stated that species differences existed among several species of tunas tested including E. affinis. In some preliminary experiments on two E. lineatus, it was found that the blood of this species could be differenti- ated from that of six other scombroids from the eastern tropical Pacific (Calkins and Klawe 1963). Other than these preliminary studies nothing has been done on subpopulation determination by serological methods. 4.2 Abundance and density (of population) Probably because of the relative commercial unimpor- tance of the species of Euthynnus, very few detailed studies have been made on the relative abundance of these fishes. Sivasubramaniam (1970) investigated the exploited stock of E. affinis along the southwest coast of Sri Lanka. He found a high degree of variability in catch rates of E. affinis within four subareas along the south- west coast which he attributed to seasonal changes in oc- currence and to the schooling behavior of this species. He concluded that the best index of the relative density of E. affinis was an average taken from the mean catch rates obtained in the four subareas. The catch rate was given as the catch in pounds per operation or trip not exceeding 24 h. Sivasubramaniam (1970) found that the index of relative density was higher (35.3) in 1968 than in 1969 (31.1). He also indicated that the mean value of relative density obtained for the southwest subarea could indi- cate the relative strength of recruitment of E. affinis along the whole southwest coast. He noted that E. affinis are first recruited into the troll fishery in the southwest subarea along the southwest coast. Sivasubramaniam (1970) estimated that a little over 600 tons of E. affinis were landed in 1969 on the south- west coast of Sri Lanka. These landings did not include those made by the nonmechanized boats. He noted that there is evidence of differential spatial distribution of E. affinis by size and that it could be possible to avoid cap- turing small fish by avoiding areas occupied by them. He indicated that the annual yield of the fishery could be considerably increased by doing this. Elsewhere in the Indian Ocean it has been recorded that E. affinis occurred in commercial quantities in Australian waters (Roughley 1951) and around Somalia (Ogilvie et al. 1954). Williams (1964) noted that there are large unexploited schools of E. affinis in east African waters and Morgan (1956) estimated that Euthynnus and Sarda represented about 0.5% of all fish by weight in the Indian Ocean. Marchal (1963) reported that the manner of fishing and total catches of E. alletteratus have had no effect on the populations of this species. Rodriguez -Roda (1966) presented long-term landings data of E. alletteratus in the Spanish fishery covering the period from 1929 to 1964. The landings were given in numbers of fish and show wide annual fluctuations but no significant trends. 4.3 Natality and recruitment 4.31 Reproduction rates See section 3.1. 5 EXPLOITATION It was noted earlier that Euthynnus generally has little or no commercial value. In many localities it appears that the typical fishery for Euthynnus is a multispecies fishery. It is not very clear whether the Euthynnus or the other species of tunas are the main targets of these fish- eries. Euthynnus usually schools together with other spe- cies of tunas, and sometimes nontunas, and the use of nonselective gear and fishing methods probably accounts for the mixed catches. However, there is some evidence of size-differentiated schooling habits in Euthynnus. In the Indian Ocean, it was found that small E. affinis tended to be found in pure schools but the larger fish were found to school with other species (Williams 1963). Williams also noted that in Madagascar, Somalia, Seychelles, Pakistan, Sri Lanka, and the west coast of India, E. af- finis is the prime objective of fisheries and specific at- tempts are made to catch this species. The FAO Yearbook of Fishery Statistics (FAO 1977) indicates that nine countries had landings of E. affinis between 1973 and 1976. In the Indian Ocean, the follow- ing countries showed landings: Maldives, Pakistan, Sey- chelles, Yemen (Arab Republic), and Indonesia; in the western Pacific: Indonesia, Malaysia, Papua New Guinea, and Philippines; and in the central Pacific: United States. Other sources (FAO 1974a, 1974b) showed that Bangladesh, India, Israel, and Sri Lanka also at one time had landings of E. affinis. In the Atlantic Ocean and the Mediterranean Sea, the following countries had landings of E. alletteratus be- tween 1973 and 1976: Angola, Bulgaria, Cyprus, Ghana, Ivory Coast, Mauritania, Morocco, Poland, Romania, Spain, United States, Venezuela, and Yugoslavia (FAO 1977). An earlier list (FAO 1974a) showed that Israel, 47 Liberia, and Turkey also at one time had landings of E. alletteratus. Euthynnus lineatus landings for Panama and the United States between 1973 and 1976 are shown in the FAO Yearbook of Fishery Statistics (FAO 1977). 5.1 Fishing equipment Silas (1967b) described the "multiple trolling" tuna fishery off the southeast coast of India (Gulf of Mannar). This is a multispecies fishery and in addition to E. af- finis, a number of other species are taken. The vessels used in the fishery are known as Tuticorin-type boats which are small sailboats ranging in length from 8.2 to 10.4 m (27-34 ft). These vessels troll seven or nine lines and carry a crew of six or seven fishermen on the smaller boats and seven to nine fishermen on the larger boats. Brined Sardinella (S. albela, S. gibbosa, and S. sirm) are used almost exclusively as bait and only rarely are artifi- cial lures used. Other methods of fishing for E. affinis in the Gulf of Mannar include bottom-set nylon nets (150 mm mesh), shore seines, drift nets (pachuvalai) of 130-150 mm mesh, and longlines (Chacko et al. 1967). In the southern sector of the Gulf of Mannar, the drift nets are set in depths of about 30 m. The longline set is composed of up to 400 hooks baited with squid and the gear is set in depths of 25 to 40 m. Off the southwest coast of India at Vizhingam, a tuna fishery is conducted almost exclusively by dugout canoes and catamarans (Bennet 1964). Including E. affinis, seven species of tunas are taken in this fishery. The other species are Auxis rochei, A. thazard, Sarda orientalis, Thunnus tonggol, T. albacares, and Katsuwonus pelamis. Bennet (1964) stated that E. affinis is one of the most important commercial species at Vizhingam. The principal fishing gears include cotton and nylon drift nets, hook and line, and occasionally shore seines. From July 1960 to October 1961, he noted that 71.4% of the landings of E. affinis were made by drift nets, 24.3% by hook and line, and only 4.3% by shore seines. In the coastal waters of Sri Lanka, mechanized boats of 3.5-ton class and 11 -ton class, in addition to the tradi- tional outrigger canoes, are engaged in the mixed tuna fishery (Sivasubramaniam 1970). The fishing gear used includes drift nets, trolling lines, pole and line, longline, and beach seines (Sivasubramaniam 1966, 1970). In Pakistan the fishing gear or methods used are trolling, longlines, handlines, and beach seines (Qureshi 1952). In the Malagasy Republic, Comoro Island, east Africa, Somalia, Seychelles, and Australia the commonest fishing method for E. affinis is trolling with either natural bait or artificial lures. Handlines and longlines are also used in Somalia (Williams 1963). In Japan no specialized fishery for E. affinis exists, apparently because consumer demand for this species is not great (Kikawa and staff 1963). Presumably, most of the E. affinis caught in Japan are taken incidentally with other species. Kikawa and staff (1963) stated that E. af- finis are taken together with Auxis, juvenile K. pelamis, T. albacares, and T. thynnus. In the coastal waters of Japan, E. affinis are taken mainly from small sailing and motorized vessels. They are also taken by pole and line. In an attempt to develop a tuna fishery in Hong Kong, the Hong Kong Fish Marketing Organization offered to buy E. affinis at a special high price in 1967 and 1968. Two boats switched to tuna fishing using a modified purse seine method. About 16 t of E. affinis were landed in the 2 yr but the fish could not be marketed at a profit and the project was abandoned (Williamson 1970). Warfel (1950) stated that the most productive method of catching tuna in the Philippines is the fish trap, called corrals, or in Tagalog, baklad. The beach seine is the next most productive. Other methods used are a Philip- pine version of a purse seine called a talakop, trolling (sibid-sibid), and occasionally a drive-in net. In Hawaii, E. affinis is taken incidentally in the live- bait pole-and-line Katsuwonus pelamis fishery and recreational troll fishery. Euthynnus alletteratus Like many of the fisheries for E. affinis, the fisheries for E. alletteratus appear to be multispecies fisheries. Along the coast of Tunisia in the Mediterranean, for ex- ample, Postel (1956) lists T. thynnus, Sarda sarda, Auxis sp., and E. alletteratus as species taken in specialized traps called madragues. Madragues are also used in the Moroccan fishery (Marchal 1963). The Tunisian fishery lands 400 to 500 tons and the Moroccan fishery 200 to 300 tons of E. alletteratus per year (Postel 1964). Fisheries for E. alletteratus along the east coast of Africa are apparently not well developed (Marchal 1963). They are caught in beach seines in Senegal, the Ivory Coast, Ghana, and Angola. Off the Ivory Coast, E. allet- teratus are also taken in sardine purse seines and in Angola they are also taken in traps similar to the madrague (Marchal 1963). On the islands of Sao Tome and Principe, E. alletteratus are taken by a type of en- circling gill net (Frade and Postel 1955). In the western Atlantic and adjacent areas, Rivas (1951) stated that the flesh of E. alletteratus is good and of commercial importance throughout the West Indies. Chilton (1949) reported that for many years E. allet- teratus has been caught in varying amounts along the Atlantic coast of the United States and along the coast of the Gulf of Mexico. Chilton's account of this species along the Atlantic and Gulf of Mexico coasts indicates that although E. alletteratus is frequently taken, and sometimes in fair amounts, no large-scale sustained fish- ery exists for this species in these areas. Mansueti and Mansueti (1962) reported on this species in Chesapeake Bay and stated that during 1951-61, E. alletteratus had been harvested commercially in pound nets and hand seines. However, the annual landings were minimal (less than 6 t per year). In addition to pound nets and hand seines, E. alletteratus in the western Atlantic has been taken by menhaden purse seines and trolling with artifi- cial lures (Chilton 1949; de Sylva and Rathjen 1961). Euthynnus lineatus Euthynnus lineatus were not fished commercially in the eastern tropical Pacific before 1972 except for the small numbers that were taken and sold fresh in the local markets of Latin American countries. This species is taken incidentally by gear used to catch other species of fish. They have been taken by tuna purse seines, by live- bait pole-and-line fishing, commercial and sport trolling, and by trolled handlines. They are taken by commercial tuna vessels of all sizes, from small albacore trollers to large purse seiners and by bait boats, and by Ecua- dorian and Peruvian canoe and raft fishermen (Calkins and Klawe 1963). Since 1972 the following commercial catches of E. lineatus have been reported in the Inter- American Tropical Tuna Commission's yellowfin tuna regulatory area (data courtesy of Calkins 7 ): Table 27.— Monthly landings (kilograms) of Euthynnus affinis at Vizhingam, India. (From Bennet 1964, table 1.) Year Catch (tons) 1972 660 1973 1,845 1974 4,043 1975 582 1976 1,673 1977 1,195 5.2 Fishing areas See section 5.3. Month 1956 1957 1958 1959 1960 1961 January 12,091 8,929 5,725 6,130 4,360 8,436 February 8,827 3,970 10,843 2,737 15,998 16,825 March 6,198 25,761 8,022 8,022 15,501 24,384 April 8,444 10,446 1,957 4,498 4,623 32,236 May 6,151 4,131 3,602 7,105 11,192 27,775 June — 3,937 3,086 1,501 2,290 1,259 July — 13,405 — 567 510 290 August 324 402 — 11,952 5,663 10,072 September — — 19,072 26,957 7,067 21,999 October 4,514 5,394 25,580 9,499 81,026 22,537 November 26,675 16,267 15,462 20,560 34,969 December 12,451 2,621 32,753 5,009 22,569 Total 85,675 95,263 126,102 104,537 205,768 165,813 factors: the differential selectivity of the gear used (troll- ing and drift net) and variation in recruitment by size in the various areas around Sri Lanka. Off east Africa, around the Comoro Islands and the Malagasy Republic, E. affinis is taken throughout the year (Williams 1963). Euthynnus affinis is present around the Philippines throughout the year but the highest catches are made from October through De- cember and April through May (Warfel 1950). Around Japan, E. affinis is taken near the Izu Islands from May to November (Kikawa and staff 1963). Young E. affinis, 5.3 Fishing seasons Euthynnus affinis Off the coast of South Africa and southwest Australia, E. affinis occur and are fished during the southern sum- , mer when surface water temperatures are at a maxi- mum (Williams 1963). In the Seychelles, the fishery is highly seasonal and takes place during the northwest monsoon (October-November to April-May), when the surface water temperature is highest (29 o -30°C). In northern Somalia, the fishery is conducted during the northeast monsoon at the time of minimum sea-surface temperature. In Pakistan, west coast of India, and Sri Lanka, E. affinis is taken throughout the year with slight local seasonal variations (Williams 1963). Bennet (1964) found that good landings of E. affinis occur during the 8 mo from October to May and the period of low catches is from June to September (Table 27) in the Vizhingam fishery (southwest coast of India). Bennet observed that the period of low catches coincides with the southwest monsoon when the seas are rough and very little fishing effort is expended. In contrast to the generalized state- ment made by Williams (1963) on the seasonal nature of the E. affinis fishery in Sri Lanka, Sivasubramaniam (1970) described a somewhat more complex situation of the seasonality of the E. affinis fishery (Fig. 36). The seasonal picture around Sri Lanka is complicated by two T. P. Calkins, Inter- American Tropical Tuna Commission, Scripps Institution of Oceanography, La Jolla, CA 92037, pers. commun. March 1978. 120 IOO 80 60 40 20 O 120 IOO 1 80 § 60 40 20 O IOO 80 60 40 20 O 140 120 IOO 80 60 40 20 O WEST 1968 / \\ / \ SP3£-«-3 N. WEST 1969 N.WEST 1968 -x DRIFT NET -° TROLL A / SOUTH 1969 rrr V^- V n,' X \ - '*~--x SOUTH 1968 S.WEST 1968 / H .<£_! I O-J. / JFMAMJ JAS0ND MONTHS JFMAMJJASOND MONTHS Figure 36.— Seasonal variation in catch of Euthynnus affinis around Sri Lanka. (From Sivasubramaniam 1970, fig. 4.) 49 15 to 25 cm long, have been caught near Aburatsu in southern Kyushu from August to October (Yabe et al. 1953). The mean monthly landings of E. affinis at two ports in Kochi Prefecture, Japan, in 1973 and 1974 (Fig. 37) indicate that E. affinis are present throughout the year near Kochi. Because of the sparse data, the significance of the three peaks in January, May, and September is not clear. In troll fishing conducted off the northeast coast of Oahu, Hawaii, from 1951 to 1955, Tester and Nakamura (1957) reported that no E. affinis were taken between De- 1200 600 [—1 — i 1—1 n n n JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC Figure 37. — Mean monthly landings of Eutkynnus affinis in Kochi, Japan, 1973-74. (Data courtesy of T. Koto, Nansei Reg. Fish. Res. Lab., and S. Kikawa, Far Seas Fish. Res. Lab., Japan.) JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC Figure 38. — Mean monthly landings of Euthynnus affinis in Hawaii, 1964-74. (Data from files of Southwest Fisheries Center, National Marine Fisheries Service, NOAA, Honolulu, HI 96812.) cember and April. Their data showed a peak in the catch rate (catch per hour) in October. However, they cautioned that the fact that no E. affinis were taken from December to April cannot be regarded as significant since only a small number of hours were expended in fishing during that period. Welsh (1949) reported good catches of E. affinis during March, April, and May 1948 and during February and April 1949 in Hawaiian waters, including the same area fished by Tester and Nakamura (1957). The mean monthly landings of E. affinis in Hawaii from 1964 to 1974 indicate higher landings from October to April (Fig. 38). The results obtained by Tester and Nakamura (1957) and Welsh (1949) are not inconsis- tent with those shown in Figure 38. Thus it appears that around Hawaii, E. affinis may be less available from May to September and more available from October to April. Euthynnus alletteratus In the Gulf of Gabes, Tunisia, E. alletteratus is found sporadically throughout the year. Off the northern coast of Tunisia, it appears in the spring and disappears in the autumn (Postel 1964). In Morocco, Postel stated that E. alletteratus appears in May and disappears at the end of November. Data presented by Ben-Tuvia (1957) on the mean monthly landings of E. alletteratus during 1950 to 1955 in Israel (Fig. 39) indicate this species is caught throughout the year and that the landings peak in May and October. Rodnguez-Roda (1966) gave a summary of the fishing seasons and the months of peak catches for E. alletteratus in the various Spanish fisheries in the Medi- terranean and the Atlantic (Table 28). The various seasonal peaks in the Mediterranean fisheries suggest that this species may make seasonal migratory move- ments. Off the coast of Senegal in the eastern Atlantic, E. al- letteratus arrive in large numbers in January-February JAN. FEB. MAR APR. MAY JUNE JULY AUG SEPT OCT NOV DEC. Figure 39.— Mean monthly landings of Euthynnus alletteratus from 1950 to 1955 in Israel. (From Ben-Tuvia 1957, table 3.) 50 Table 28. — Fishing seasons for Euthynnus alletteratus in Spain. (From Rodriguez- Roda 1966, table 3.) Months of Region Fishing season peak catches North coast jj Jan. to Dec. Sept. and Oct. Northwest coast I Atlantic June to Dec. Oct. Southwest coast | Ocean Feb. to Dec. Aug. to Oct. Canary Islands / Jan. to Dec. Dec. to Mar. Southern coast | Jan. to Dec. Sept. and Oct. Southeast coast 1 Mediterranean Jan. to Dec. Sept. and Oct. Eastern coast 1 Sea Apr. to Dec. July to Oct. Balearic Islands / Jan. to Dec. May to July and May- June (Postel 1955b). They are present all year in the region of Cap Vert (Marchal 1963). Off the Ivory Coast, Marchal (1963) stated that E. alletteratus are found throughout the year along the coastline but that the catches peak in February. He stated that E. allet- teratus are caught in Angola starting in October, the catches peak in February and March, and become non- existent in May-June. In the western Atlantic, Chilton (1949) suggested that E. alletteratus make seasonal migrations along the U.S. coast. In May and June they have been reported moving north to North and South Carolina and in August and September they have been caught along the coasts of New Jersey and New York. Observations made from September 1952 to August 1953 on anglers' catches landed at Miami, Fla., indicate that 87% of the catches were made from March through August including a peak in July (de Sylva and Rathjen 1961). de Sylva and Rath- jen stated that there is evidence of a general drift of E. al- letteratus out of the Miami area toward the south during the winter and that they occur further north along the coast during the summer. Euthynnus lineatus Euthynnus lineatus is taken throughout the year in all areas of its distributional range. Although information on the seasonal abundance is not very clear, Calkins and Klawe (1963) cited an Ecuadorian census of fishermen which indicated that E. lineatus was most abundant from May to September in the open coastal areas and from January to March in the Gulf of Guayaquil. 5.4 Fishing operations and results 5.42 Selectivity The beach seines, principally used in the Sri Lanka fishery for E. affinis, are not size selective. Surface troll- ing, handlines, and longlines that are used in the Indian Ocean are also not selective (Williams 1963). Calkins and Klawe (1963) stated that E. lineatus are taken by nonselective gear. de Sylva and Rathjen (1961) suggested that the com- mercial trolling gear used to catch E. alletteratus may possibly be selective for a certain size range of fish (see section 4.13). 5.43 Catches With the exception of the Philippines and Indonesia where a fair amount of E. affinis is landed, the species of Euthynnus are nowhere the basis of important large commercial fisheries. To illustrate the magnitude of the fisheries for Euthynnus, from 1965 to 1976 the total world landings for all the species fluctuated from 37,000 to 88,000 t (Fig. 40). In comparison, the annual world pro- duction of K. pelamis has ranged from 300,000 to 350,000 t in 1966-71 (Matsumoto 1974). In Figure 40 is also plotted the total world production of E. affinis and E. alletteratus from 1965 to 1976. The world landings of E. affinis varied from 29,900 to 84,800 t annually and that of E. alletteratus from 4,600 to 9,500 t. Euthynnus affinis constituted 77.1 to 97.0% of the total for Euthynnus during this period. Only small amounts of E. lineatus have been reported in the statistics. It should be pointed out, however, that the world production of Euthynnus, as indicated by the statistics given above, is probably underestimated. It may happen that because only small amounts of Euthynnus are taken, they are lumped together with other species of tunas, or together with other miscellaneous species. Other problems asso- ciated with collecting catch statistics in the Indian Ocean are discussed in FAO (1973). Thus the figures for Euthynnus are probably not only underestimated but are also subject to inaccuracies. The production of E. affinis from 1973 to 1976 in the Pacific and Indian Oceans is given in Table 29. As noted earlier, the Philippines and Indonesia have compara- tively large fisheries for Euthynnus. The Philippines landings of E. affinis fluctuated from 9,447 to 24,000 1 be- 100 I 1 ! 1 1 1 1 i i i i TOTAL Euthy nnus y^^^^o /• It II II II II II II II / A \ / V / o II ' X E. affinis /E. alletteratus i i i i i i i E. lineatus 1965 1967 1969 1971 1973 1975 Figure 40. — World landings of Euthynnus. (Data from FAO 1974a, 1976, 1977.) 51 tween 1973 and 1976. The landings in Indonesia fluctu- ated between 31,600 and 41,616 t (Pacific Ocean) and 5,200 and 8,609 t (Indian Ocean) during the same peri- od. Although the FAO Yearbook of Fishery Statistics does not show any landings of E. affinis in India from 1973 to 1976, according to Bennet (1964), 85.7 to 205.8 t were produced in Vizhingam, India, between 1956 and 1960 (see Table 26). In Hawaii, where E. affinis is taken incidentally in the pole-and-line fishery for K. pelamis, between 8.0 and 43.9 t were recorded during the 14-yr pe- riod from 1964 to 1977. In Japan, production figures for E. affinis are not readily available because they are com- bined with those of other species (Kikawa and staff 1963). The world landings of E. alletteratus from 1973 to 1976 are shown in Table 30. It can be seen that only relatively small quantities of this species are taken in any of the fisheries. During the period from 1973 to 1976, the total annual production of E. alletteratus in the western Atlantic amounted to slightly over 500 t. In the eastern Atlantic, during the same period, the total annual Table 29.- Landings of Euthynnus affinis in metric tons. FAO 1977.) (From Area 1973 1974 1975 1976 Pacific Ocean total '60,850 58,233 61,654 59,003 Indonesia 31,600 38,507 39,625 41,616 Malaysia 5,000 8,145 9,963 7,810 Papua New Guinea '250 250 30 100 Philippines 24,000 11,315 12,013 9,447 United States 16 23 30 Indian Ocean total 16,300 23,132 23,156 '23,028 Indonesia 5,200 8,609 7,710 7,927 Maldives 1,000 800 400 1,000 Pakistan 9,600 13,113 14,470 13,575 Seychelles 300 350 250 200 Yemen (Arab Republic) 200 260 326 '326 Total E. affinis landings ■77,150 81,365 84,810 '82,031 'Estimated. Table 30.-— Landings of Euthynnus alletteratus in metric tons. (From FAO 1977.) Area 1973 1974 1975 1976 Western Atlantic Ocean total 300 382 360 506 Poland — — 2 — United States 9 1 5 Venezuela 300 373 357 501 Eastern Atlantic total 2,000 '4,285 '2,515 '1,967 Angola 900 1,287 449 '449 Bulgaria — 8 — Ghana — 66 138 76 Ivory Coast 1,583 860 400 Mauritania 1,000 '1,000 '1,000 '1,000 Morocco 0. 46 14 32 Poland — 6 — — Romania 100 297 46 10 Spain — — — — Mediterranean Sea total 700 13 27 H Cyprus 5 7 7 Morocco 5 — Spain 700 — — — Yugoslavia 3 20 1 Total landings 3,000 '4,680 '2,902 '2,481 landings fluctuated between 1,967 and 4,285 t, and in the Mediterranean Sea they did not exceed 700 t during the same period. Although the FAO Yearbook of Fishery Statistics does not show any figures for E. alletteratus from Tunisia, Postel (1964) reported that 400-500 tons are landed an- nually in Tunisia. Calkins and Klawe (1963) stated that most of the landings of E. lineatus are probably made by small boats in Latin America and that they go unrecorded. They further noted that landings are sometimes recorded in Mancora, Peru, but it is not known what proportion they make up of the actual total landings even in the immedi- ate area of Mancora. Tuna purse seiners sometimes in- advertently set on E, lineatus but these catches are dumped overboard. However, estimates of the amount caught have been recorded in the vessels' logbooks which indicate that amounts from 1 to 100 tons have been caught (Calkins and Klawe 1963). In years when large amounts of tuna are caught by setting on schools, as op- posed to setting on porpoises, large quantities of E. lin- eatus are dumped overboard (Klawe 8 ). LITERATURE CITED ALVERSON, F. G. 1963. The food of yellowfin and skipjack tunas in the eastern tropi- cal Pacific Ocean. [In Engl, and Span.] Inter-Am. Trop. Tuna Coram. Bull. 7:293-396. ANGOT, M. 1959. Tuna fishing investigations in the South Pacific. South Pac. Coram. Q. Bull. 9(41:48-53. BEARDSLEY, G. L„ Jr., and W. J. RICHARDS. 1970. 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It is hoped that synopses in this series will be useful to other scientists initiating investigations of the species con- cerned or of related ones, as a means of exchange of knowledge among those already working on the species, and as the basis for comparative study of fisheries resources. They will be brought up to date from time to time as further information becomes available. The documents of this Series are issued under the following titles: FAO CSIRO INP NMFS Symbol Fisheries Synopsis No. FIR/S Fisheries Synopsis No. DFO/S Sinopsis sobre ta Pesca No. INP/S Fisheries Synopsis No. NMFS/S Synopses in these series are compiled according to a standard outline described in Flb/S1 Rev. 1 (1965). FAO, CSIRO, INP, and NMFS are working to secure the cooperation of other organizations and of individual scientists in drafting synopses on species about which they have knowledge, and welcome offers of help in this task. Additions and corrections to synopses already issued will also be most welcome. Comments on individual synopses and requests for information should be addres- sed to the coordinators and editors of the issuing organizations, and suggestions regarding the expansion or modification of the outline, to FAO: FAO: Fishery Resources and Environment Division Aquatic Resources Survey and Evaluation Service Food and Agriculture Organization of the United Nations Via delle Terme di Caracalla 00100 Rome, Italy CSIRO: CSIRO Division of Fisheries and Oceanography Box 21 Cronulla, N.S.W. 2230 Australia INP: Instituto Nacional de Pesca Subsecretaria de Pesca Secretaria de Pesca Secretaria de Industria y Comercio Carmona y Valle 101-403 Mexico 7, D.F. NMFS: Scientific Editor National Marine Fisheries Service, NOAA Auke Bay Fisheries Laboratory P.O. Box 155 Auke Bay, AK 99821 U.S.A. Consolidated lists of species or groups covered by synopses issued to date or in preparation will be issued from time to time. Requests for copies of synopses should be addressed to the issuing organization. The following synopses in this series have been issued since January 1977: FIR/S1 13 Synopsis of biological data on the perch, Perca fluviatilis and flavescens December 1977 NMFS/S116 Synopsis of biological data on the red progy, Pagrus pagrus (Linnaeus) May 1978 NMFS/S1 17 Synopsis of biological data for the winter flounder, Pseudopleuronectes americanus (Walbaum) November 1978 NMFS/S123 Synopsis of biological data on the rock crab, Cancer irroratus Say May 1979 PENN STATE UNIVERSITY LIBRARIES UNITED STATES DEPARTMENT OF COMMERCE NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION NATIONAL MARINE FISHERIES SERVICE SCIENTIFIC PUBLICATIONS STAFF ROOM 450 II07N E 45THST SEATTLE. 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