McGOWAN and RICHARDS: BLUEFIN TUNA LARVAE 



quently moved offshore. A 3.0 mm bluefin larva 

 estimated to be only three days old was collected 

 here at station 728. 



The third group of stations with bluefin tuna 

 larvae were all farther offshore in water more 

 than 700 m deep. The surface water here had a 

 narrow range of sahnities from about 36.0 to 36.5 

 ppt. Temperature at the surface in this region 

 ranged from approximately 24.5° to 27.5°C. 

 Bluefin tuna larvae were found where the sur- 

 face water was in the center of this temperature 

 range: from 25.5° to 26.5°C. Bluefin tuna larvae 

 from the northern positive stations and the 

 southern shelf edge stations were also found at 

 the same surface sahnities and temperature, ex- 

 cept for station 634 where the temperature was 

 24.8°C (Fig. 8). 



Previous Captures of Bluefin Tuna 

 Larvae off Cape Hatteras 



In 1966 three bluefin tuna larvae were col- 

 lected off Cape Hatteras (Berrien et al. 1978). 



Figure 7. — Chart showing the position of the edge 

 of the Gulf Stream on 15 May 1985 relative to two 

 stations (727 and 728) where bluefin larvae were 

 collected 14 May. The filament shown in Figure 6 is 

 not visible and the stations are now in colder water 

 inshore of the edge of the Stream. (Redrawn from 

 NOAA Gulf Stream System Flow Chart #2450, 15 

 May 1985.) 



One larva 7.7 mm long was collected 20 April in 

 235 m water depth. Two larvae, 5.4 mm and 9.3 

 mm SL, were collected 23 June over 269 m and 

 68 m, respectively. The stations where these 

 larvae were collected are at the shelf edge or just 

 inshore of it. Contour plots of surface tempera- 

 ture (Fig. 9) and salinity (in Bemen et al. 1978) 

 show that the Gulf Stream front was inshore of 

 the stations where bluefin larvae were caught. 

 Temperature cross-sections show clearly that 

 the stations where bluefin tuna larvae were col- 

 lected were in Gulf Stream water (Fig. 9). The 

 larva caught in April was in water with lower 

 surface temperature and lower surface salinity 

 than typical (Fig. 8) for the stations where blue- 

 fin tuna larvae were present in 1985. The two 

 larvae caught in June were in water more typical 

 for bluefin tuna larvae but near the highest salin- 

 ities and temperatures (Fig. 8). 



27* N 



623 



