HANAN: BLUEFIN TUNA FISHERY 



4 - 



10 



60 80 100 120 140 160 180 



H 3 



Z 



UJ 



o 



DC 



UJ 



0. 2 



1963-1971 and 1974 

 N = 9,980 



,1,LJJ " 1 



60 80 100 120 140 160 180 



FORK LENGTH (cm) 



Figure 15.— Composite bluefin tuna percent length frequen- 

 cies. Upper graph summarizes length-frequency samples for 

 1952-65. and lower graph summarizes length-weight-age sam- 

 ples for 1963-71 and 1974. 



ing grounds and fishing season, indicating good 

 mixing with the untagged population. 



Gulland (1963) described a method of estimat- 

 ing fishing mortality from tagging experiments; 

 this method was modified and applied to the 



z 



UJ 



o 



°- 4 



NORTH OF 32° N. 

 N = 30.444 



60 80 100 120 140 160 180 



10 



8 - 



z 



UJ 



o 



oc 



UJ 



0. 4 



SOUTH OF 32° N. 

 N=31,773 



60 80 100 120 140 160 180 



FORK LENGTH (cm) 



Figure 16.— Bluefin tuna percent length-frequency compos- 

 ites for 1952-65, north (top) and south (bottom) of lat. 32°N. 



bluefin data. It was assumed that the number of 

 tags returned per unit of effort is proportional to 

 the CPUE, and no provision was made for immi- 

 gration or emigration. For any period following 

 tagging, an estimate of catchability (q) would be 

 the number of tags returned per unit of effort di- 

 vided by the initial number released. When these 



Table 9. — Total number of returned bluefin tags summarized by latitude 

 of release and of return. Totals are for areas between a given parallel and 

 the next higher parallel. 



117 



