BLACKBURN and WILLIAMS: DISTRIBUTION AND ECOLOGY OF SKIPJACK TUNA 



125° * I20°W h5*W 



IS«N. 



CATCH/LINE- HR. 



iOn*. 



5«N 



5*S 



.Km 



•_„ — ■— • — • — ' — • — • — 

 • .; ! 



JORDAN 

 CROHWELL 



.eru 



S'U 



ys 



Hyw 



Figure 5.— Relative abundance of skipjack in catch/line-hour, 

 cruises Jordan bl-Cromwell 51, November-December 1970. 



percent of skipjack in three broad size categories 

 for the two cruises. The most significant feature 

 is that 13.3% of skipjack were < 45 cm in 

 November-December 1970, as against 2.9% on the 

 next cruise. 



The fish < 45 cm were not distributed over a 

 large part of the area, as fish >45 cm were, in 

 November-December 1970. Of the small fish, 16 

 (85%) were from areas north of the NECC, lat. 10° 

 to 14°N, and the remaining 3 (15%) from south of 

 the NECC, lat. 0°30' to 4°N; none were found in the 

 NECC or south of the equator. Table 7 shows small 

 skipjack ( < 45 cm) as percent of total in the lati- 

 tudinal zones north of 10°N. It appears that the 



I5'N 



lO'N 



IIS'W 



_1 L_ 



CATCH/LINE-HR. 



<0.05 

 0.05 - I 

 I - 0.2 

 02-0.4 

 >0.4 



5*N- 



0'- 



5'S 



-lO'N 



I5'N 



-5*N 



5'S 



I20*W 



Figure 6.— Relative abundance of skipjack in catch/line-hour, 

 cruise Jordan 60, March-April 1971. 



Table 5.— Percent' of total number of skipjack schools encoun- 

 tered on track, by 1-h periods (all fishing days combined): Cruises 

 Jordan bl-Cromivell 51, November-December 1970, and Jordan 

 60, March- April 1971. 



'Adjusted data, see text p. 388. 



^Mean start 0556 h and 0539 h on Jordan 57-Cromwell 51 and 

 Jordan 60 respectively. 



389 



