1oxfitatesMA(mte,'ianJIllseum PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK 24, N.Y. NUMBER 1765 APRIL 6, 1956 Tunas of the Genus Thunnus of the Northern Caribbean BY HARVEY R. BULLIS, JR.,' AND F. J. MATHER, 1112 During Cruise 30 of the United States Fish and Wildlife Service ex- ploratory fishing vessel "Oregon," in April, 1955, six species of tuna were caught on longlines in the northern Caribbean. The species of tunas taken at the 11 stations occupied (see fig. 1) are listed in table 1. Additional information on the distribution of tunas was obtained from Captain Archie Cross of the M/V "Santo Antonino" and Captain Ed Saarinen of the M/V "Hermes II," who have been fishing with longlines in this area. The yellowfin tuna, Thunnus3 albacares (Bonnaterre), the blackfin tuna, Thunnus atlanticus (Lesson), and the oceanic bonito, Katsuwonus pelamis (Linneaus), are well-known indigenes of the region (Beebe and Tee Van, 1928, 1936; Rivas, 1951; Mather and Schuck, 1952; Rawlings, 1953). Most reports of the albacore, Thunnus alalunga (Gmelin), have been based on T. atlanticus, and there are no records of this species, sub- stantiated by specimens, from the western North Atlantic (Rivas, 1951, pp. 220, 222, 223). Specific data on the presence of bluefin tuna, Thun- nus thynnus (Linneaus), in the Caribbean area are lacking, although there is one known capture from the northern coast of Jamaica (personal communication). We know of no previous records of the Atlantic big- 1 United States Fish and Wildlife Service, Pascagoula, Mississippi. 2 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts (Contri- bution No. 774, Woods Hole Oceanographic Institution). 3 We have followed Fraser-Brunner (1950) and Rivas (1951) in considering the genera Neothunnus, Parathuinnus, and Germo as either synonyms of the genus Thu-nnus or subgenera of that genus. tt -I I-III IlIl1I : S IIoe Io bI IIIme z C A<t~~~~I-I CT o ata ~~~~~~II Ii i iD~~~~~o o; - t- - t- - t- r- 0 0 0 0 0 0 0 0 0 0 0 0 i r- \r r oo 70\C 0 0 0 0 0 0 o 0 o 0 0 o: - o c _ O O-* \0 2 - 00oo 0sON o eD oooo m ON \ C\ a- C\C C' eqN eq NNNN 1956 . BULLIS AND MATHER: TUNAS. 3 85- so* 75 70- 1297'' @ 20 #8 21287t 129 20 b5-5 0 k1296- PN -4 1288e~~2 1289 -5. ~~~~~~~~~~~~~~~129019 ~ 5 85* 80, T5 700 FIG. 1. Positions of longline stations in the northern Caribbean. eye tuna, Thunnus obesus (Lowe), from west of the Azores. The listing of this little-known species among the fishes of Port-au-Prince Bay by Beebe and Tee Van (1928) was later (1936) placed in the synonymy of T. atlanticus by those authors. Morice and Cadenat (1952) and Morice (1953) synonymized T. atlanticus with T. obesus, and it appears that the species to which they refer as occurring off the West Indies was the former. Beebe and Tee Van (1936) showed clearly that T. atlanticus (placed in the genus Parathunnus by them) was a valid species. Fraser-Brunner (1950) incorrectly placed it in the synonymy of T. alalunga. Having ex- amined freshly caught specimens of T. obesus, T. atlanticus, and T. alalunga, we have no doubt that they are different and valid species. A decisive character in separating T. atlanticus from the others is its gill-raker count. Beebe and Tee Van counted the gill rakers on both the left and right arches of 58 blackfins and found the following range of counts: for the lower limb, 15 to 18; for the upper limb, four to six; total number, 20 to 24. One of us (Mather) has taken gill-raker counts from many T. atlanticus captured between Rio de Janeiro and Cape Cod. These are in very close agreement with those of Beebe and Tee Van, ranging from 15 to 18 for the lower limb, four to seven for the upper, and from 20 to 23 in total number. Rivas (1951) gives a slightly higher range of lower rakers (15-19), but states that his studies are in complete accord with those of Beebe and 'Tee Van. In contrast, the count given by Fraser-Brunner for T. obesus is 18 to 25 lower, and eight to 13 upper, and that for T. alalunga by Letaconnoux (1950) is 18 to 22 lower, seven to 10 upper, and 26 to 31 total. The counts obtained by us are consistent 4 AMERICAN MUSEUM NOVITATES NO. 1765 ~ i .n 4.X.,E..iz ' % '.'.E ' .'. _4 FIG. 2. A yellowfin tuna, Thunnus albacares (upper), compared with the heavier big-eye tuna, Thunnus obesus (lower). The fork length of each fish is approximately 150 cm. with these figures, being 19 lower, eight to nine upper, and 27 to 28 total for T. obesus,I and 19 to 22 lower, seven to nine upper, and 27 to 31 total for T. alalunga. Thus T. atlanticus is readily separable from both T. obesus and T. alalunga on the basis of total gill-raker counts, and in most cases by the lower limb count. The pectoral of the albacore is usually much longer (1 to 1.62 times head length) than that of the blackfin tuna (0.8 to 1.2 times head length), but the species intergrade in this respect. In addition, the color of the finlets distinguishes T. atlanticus from the other species. All the finlets of T. obesus and the dorsal ones of T. 1 Rivas obtained counts of 20 to 22 lower, nine upper, and 29 to 31 total for two eastern Atlantic specimens (personal communication). 2 From measurements of Bay of Biscay specimens 51 to 80 cm. long (Navaz, 1950). For the larger specimens measured by us, the pectoral varied from 1.35 to 1.6 times head length. 1956 _~~~~~~~~~~~~~~~~~~~~~~~~~BULLIS AND MATHER: TUNAS 5 cm. in for length.III duk steel siilt tha it is jidnicalwith T.obess.Temxiu sieatrbue --->-"-----E FIG. 3. A yellowfin tuna (upper) compared with an albacore, Thunnus alalunga (lower). The yellowfin is about 100 cm., and the albacore about 96 cm., in fork length. al5lunga are predominantly yellow. Those of T. atlanticus are not yellow, the dorsal ones usually being of a dusky brown color, and the anals dusky steel. The total size range of T. atlanticus also appears to preclude the pos-i sibility that it is identical with T. obesus. The maximum size attributed to T. atlanticus is 60 pounds (Mowbray, 1935), but our own observa- tions lead us to be-lieve that individuals weighing over 25 pounds are very rare. On the other hand, our specimens of T. obesus weighed about 175 pounds each, and Frade (1931) examined individuals up to 188 cm. long, probably weighing about 275 pounds. In addition to this disparity in recorded sizes., the fact that T. atlanticus spawns at a very small size (less than 10 pounds) suggests that its maximum size cannot compare with that attained by T. obesus. 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