FISHERY BULLETIN: VOL. 69, NO. 3 



predominant year of the Geronimo surveys) , 3.7 

 times more adult yellowfin tuna than adult big- 

 eye tuna were captured by Japanese longliners 

 in the same general area (Wise, see footnote 3) . 



SKIPJACK TUNA LARVAE 



Richards (1969) found that distributions of 

 skipjack tuna larvae differed from those of yel- 

 lowfin and bigeye tunas, particularly when 

 surface temperature values were below 26° C. 

 Apparently skipjack tuna larvae are able to 

 tolerate lower temperatures than the other two 

 tunas. In the area covered by Geronimo cruise 3, 

 distributions of larval skipjack tuna (Figure 9) 

 were similar to those of yellowfin tuna larvae, 

 but fewer were caught. The lesser quantities 

 may have resulted from the sampling method 

 used; surface collections may not adequately 

 sample the species. 



On Geronimo cruise 3, skipjack tuna larvae 

 were collected in water temperatures that ranged 

 from 27.6° to 29.7° C and salinities from 34.4^*. 

 to 35.5';V. On Geronimo cruise 4 (Figure 9) the 

 species was infrequently collected, although 

 larvae had been commonly collected in the same 

 region on Equalant II. Skipjack tuna larvae 

 were found in the warmer water (24.4°-25.8° C) 

 on Geronimo cruise 4, which was also true of 

 Equalant II (see Richards, 1969: 298). On 

 Geronimo cruise 5 (Figure 9) larval skipjack 

 tunas were taken at only four stations, presum- 

 ably an artifact of the sampling method. Off 

 Sierra Leone, these larvae were found at only 

 seven stations, perhaps again an artifact of 

 sampling. 



LITTLE TUNNY LARVAE 



also noticeably different from that of the other 

 tuna species. The temperatures for the larvae 

 ranged from 22.7° to 29.3° C and the salinities 

 from 32.7^',r to 35.4;,,. Apparently little tunny 

 larvae can tolerate a wider range of physical 

 conditions than can the larvae of the more 

 oceanic tunas — skipjack, yellowfin, and bigeye. 



Auxis sp. 



Larvae of Auxis (frigate mackerels) are un- 

 questionably the most abundant scombrid larvae 

 found in these tropical waters. This abundance 

 holds true for the eastern Pacific (Klawe, 1963) , 

 as well as for the eastern Atlantic (Figure 11). 

 (We are aware that Auxis may be two species, 

 but as yet methods for distinguishing their 

 larvae have not been satisfactorily developed.) 

 In the northwestern Gulf of Guinea, Auxis larvae 

 were collected mostly nearshore, though a few 

 specimens were found offshore. Auxis was the 

 only species widely distributed off Sierra Leone. 

 One reason for its abundance may be the wide 

 tolerance of the larvae for temperature and sa- 

 linity — Auxis larvae were found in water with 

 temperatures as low as 21.6° C and as high as 

 30.5° C, the widest temperature range found for 

 any tuna larvae we studied. The salinity range 

 of the species was 33.2/,'r to 35.9/,c. 



ACKNOWLEDGMENTS 



This manuscript was reviewed by Elbei't H. 

 Ahlstrom, National Marine Fisheries Service, 

 La Jolla, Calif.; Witold L. Klawe, Inter-Amer- 

 ican Tropical Tuna Commission, La Jolla, Calif. ; 

 and Walter M. Matsumoto, National Marine 

 Fisheries Service, Honolulu, Hawaii. We appre- 

 ciate their effoi-ts in our behalf. 



Little tunny larvae were collected during the 

 Equalant surveys but the data have not yet been 

 evaluated. In the northwestern Gulf of Guinea 

 and off Sierra Leone, little tunny larvae were 

 collected during each Geronimo cruise (Figure 

 10). Unlike the other species, they were not 

 collected on the outer ti-ansects near the equator. 

 The distribution of the larvae of this species, 

 as it related to temperature and salinity, was 



LITERATURE CITED 



Ahlstrom, E. H. 



1959. Vertical distribution of pelagic fish eggs and 

 larvae off California and Baja California. U.S. 

 Fish Wildl. Serv., Fish. Bull. 60: 107-146. 

 Be.ard.sley, G. L., Jr. 



19C9. Distribution and apparent relative abundance 

 of yellowfin tuna (Tluinniis albacares) in the east- 

 ern tropical Atlantic in relation to oceanographic 

 features. Bull. Mar. Sci. 19: 48-56. 



564 



