478 



Fishery Bulletin 92|2). 1994 



Feb. 



2.08 0.48 



ence of a steep thermocline during 

 the entire year. The range and 

 mean of sea water temperature at 

 the calculated depths of longline 

 hooks, and the mean depth and 

 temperature at the top and bottom 

 of the thermocline in May-June 

 and November-December are 

 shown in Table 6. All longline 

 hooks were located in or below the 

 thermocline (Fig. 7). During Nov.- 

 Dec. the thermocline was about 30 

 m deeper than during May-June. 



Male blue shark catches from 

 February to June were concen- 

 trated among central, deeper 

 hooks, whereas in the second half 

 of the year they were more uni- 

 formly distributed (Fig. 8). Male 

 catch was significantly different 

 among hooks from February to June (chi-square; 

 P<0.005), but not from July to December (0.10 < 

 P<0.25). The difference of male catches, on hooks 3, 

 4, and 5 between February-June and July-Decem- 

 ber was significant (0.05 < P<0.10). The relative dis- 

 tribution of female blue shark catches along longline 

 hooks from February to July (Fig. 8) was different 

 from that of males; the highest catches took place on 

 hooks 2 and 5. The difference between male and fe- 

 male catches among hooks during February to July 

 was significant (0.01 < P<0.05). The distribution of 

 male and female catch among hooks suggests that 

 males were distributed in shallower waters between 

 July and December than between February and June 

 and that females from February to July had a shal- 

 lower distribution than males. 



From February to July, CPUE for females was 

 highest in hooks 2 and 5 (130 to 165 m), and CPUE 



Table 4 



Blue shark, Prionace glauca, monthly sex ratio (number of males per 

 female), in the southwestern equatorial Atlantic Ocean. 



Mar. Apr. May Jun. Jul. Aug. Sep. 



Oct. 



Nov. 



Dec. 



1.29 



1.79 2.71 2.35 6.00 54.00 25.00 16.00 8.50 



for males in hooks 3 and 4 (165 to 180 m) (Table 5). 

 The corresponding range of sea water temperature 

 was 13.8° to 20.4°C for females and 12.9° to 17.1°C 

 for males (Table 6). Male catch among hooks from 

 July to December, was much more uniform, suggest- 

 ing a depth range for males from 90 to 180 m (Table 

 5), or from about 15° to 28°C (Table 6), up to the top 

 of the thermocline (Fig. 7). 



Discussion 



The results on horizontal distribution agree with 

 those of Hazin et al. (1990), corroborating the oce- 

 anic character of blue shark (Fig. 2). Abundance was 

 also clearly related to bottom depth. The mean CPUE 

 of blue shark in areas of bottom depths greater than 

 1,000 m was 10 times higher than in shallower ar- 

 eas. The lower abundance of blue sharks west of 35°W 



