372 



Fishery bulletin oJ the fish and wildlife service 



CO 



01 

 UJ 

 H- 

 UJ 



< 



120 



Figure U. 



160 



200 



240 280 320 



HEAD LENGTH mm. 



360 



4 00 



-Relations between diameter of iris and length of head. Open circles and fine line represent Costa Rican data; 

 solid circles and heavy line represent Hawaiian data. 



teristics of yellowfin tuna from the Hawaiian 

 Islands and from the American west coast, there 

 is no doubt that these two populations are to be 

 regarded as distinct. The possibility of some mix- 

 ing between them is not excluded, but if any 

 exists it must be sufficiently small to permit the 

 two populations to maintain their characteristic 

 differences. 



The statistical comparison of body-proportion 

 data on tunas from different regions by regression 

 analysis is beset with difficulties which are be- 

 yond the scope of this paper to deal with, and 

 which seem not to be critical in this mstance where 

 the differences dealt with are of sufficient magni- 

 tude that sensitive methods are not required. The 

 problem merits, however, fm-ther attention since 

 it will become acute where differences to be meas- 

 ured are small. 



This problem may be avoided by employing 

 denumerable characters which are not size-con- 

 nected. Gill-raker counts seem to be a useful 

 character of this sort. The Hawaiian and west- 

 coast yeUowfin-tuna populations are quite distinct 

 with respect to mean gUl-raker coimt. 



The fact, brought out by this study, that the 

 yellowfin tuna of the central Pacific belong to a 

 popidation distinct from that along the American 

 west coast, has important implications in the devel- 

 opment and management of the tuna fisheries. 

 Since the yellowfin tuna of these regions belong 

 to different populations which do not freely inter- 

 mix, a fishery on one can have no effect on the 

 abundance of the other. The fishery along the 

 west coast is not tapping the entu-e yeUowfin- 

 tuna resource of the Pacific. 



