FISHERY BL'LLETIN: VOL. 69, NO. 5 



that the difference was because of increased sam- 

 pling intensity on Geronimo cruise 3. Wide- 

 spread spawning was seen near the equator, liow- 

 ever, on both Equalant I and Geronimo cruise 3. 

 An indication of this equatorial spawning is evi- 

 dent in cruise 5 (Figure 7). During Geronimo 

 cruise 4, the distribution of larvae was reduced 

 from that seen on cruise 3, averaging 5.2 larvae 

 per 1000 m^ of water strained. Again the situ- 

 ation differed from that found in Equalant II 

 during which almost no larvae were taken, 

 probably because of light sampling. 



Richards (1969) found no yellowfin tuna 

 larvae in waters with temj^eratures lower than 

 26° C, and indicated that the presence of yellow- 

 fin tuna larvae may depend on water tempera- 

 ture. During the Geron imo cruises, with one ex- 

 ception, yellowfin tuna larvae were collected in 

 waters warmer than 24° C. Hence, the lower 

 limit of 26° C for surface temperature set for 

 the presence of yellowfin tuna larvae by Richards 

 (1969) should be lowered to 24° C. Surface 

 water temperatures were above 27° C at all sta- 

 tions sampled during cruise 3, and yellowfin tuna 

 larvae were found between 27.9° and 29.7° C. 

 During cruise .5 (also the "warm season") , sur- 

 face tem])eratures ranged from 22.5° to 29.9° C 

 but yellowfin tuna larvae were found within a 

 range of 24.9° to 29.5° C. During cruise 4 (the 

 "cool season"), surface temperatures ranged 

 from 19.3° to 25.5° C; yellowfin tuna larvae were 

 found only in water with temperatures higher 

 than 24° C except at one station with a temper- 

 ature of 23.6° C. During cruises 3, 4, and 5, 

 surface salinity values ranged from SS'/i, to 36',,^. 

 The yellowfin tuna larvae were rarely encount- 

 ered when salinity fell below 34/i, but were 

 common between 34'/;, and 36%c. 



In the area off Sierra Leone, yellowfin tuna 

 larvae were encountered in water tempei-atures 

 higher than 25° C (Figure 7), the area south of 

 the 25° C isotherm. That area was not covered 

 during the "cool season" by Geronimo crui.ses 

 hut did receive minor coverage on Equalants I 

 and II, which resulted in the collection of some 

 tuna larvae, particularly on Equalant II. Water 

 temperatures were 26° C or higher at the Equal- 

 ant stations where collections wei'e made. Co- 

 nand (1970) found yellowfin tuna larvae in 



waters warmer than 27° C off Senegal. 



The Gulf of Guinea and contiguous waters ac- 

 count for much of the Atlantic tuna catch. 

 Beardsley's (1969) discussion of the relation of 

 oceanographic features to adult yello\vfin tuna 

 distributions in that area is of interest to the 

 present study. In his summary charts of adult 

 yellowfin tuna distributions, some catch rates 

 are high in areas of cool water where the larvae 

 do not occur, which indicates that an abundance 

 of adults may not indicate abundance of larvae. 

 Surface fishing was carried out by the Geronimo 

 during cruises 3, 4, and 5 and it was interesting 

 to note that there was no apparent relation be- 

 tween sightings of surface schools and location 

 of larvae. 



BIGEYE TUNA LARVAE 



The distribution of bigeye tuna larvae in the 

 northwestern Gulf of Guinea approximated that 

 of yellowfin tuna larvae (Figure 8), but the 

 average number per 1000 m^ of water strained 

 was less than for yellowfin tuna larvae. (A 

 similar pattern was noticed on the Equalant 

 surveys) . Off Sierra Leone, the species was col- 

 lected as often as yellowfin tuna (29 bigeye tuna 

 stations compared with 28 yellowfin tuna sta- 

 tions), but the average number of bigeye tuna 

 larvae collected was less than that of the yellow- 

 fin tuna. Larvae of bigeye tuna — like the yellow- 

 fin tuna larvae — were collected offshore, south 

 of the 25° C isotherm. The apparent abundance 

 of bigeye tuna larvae, compared with yellowfin 

 tuna larvae, closely resembles that of the adults, 

 as shown in the Japanese Atlantic longline data 

 ( Wise') . During the Equalant surveys, 3.0 times 

 more yellowfin tuna larvae than bigeye tuna lar- 

 vae were captured. In 1963 (the year of Equal- 

 ants I and II) 3.4 times more yellowfin tuna 

 adults than bigeye tuna adults were captured by 

 Jai)anese longliners in the same general area 

 (Wise, see footnote 3). During the Geronimo 

 surveys 3.9 times more yellowfin tuna larvae than 

 bigeye tuna larvae were captured. In 1964 (the 



' Wise, .1. P. 1969. .'^ome basic stati.stics of the .At- 

 lantic tuna fi.shrrie.s. B.C.F. Tropical Atlantic Biological 

 Laboratory, [Miami, Fla.,] Data Summary No. 8, 14 p. 

 [Processed.] 



562 



