120° 140° 160° 180° 160° 140° 120° 100° 80° 



100° 80° 



Figure 16. Index to Racial Difference of Yellowfin 

 Between Sannple Localities. To understand the relationship be- 

 tween tuna stocks we have compared the body proportions of 

 yellowfin tuna from various parts of the Pacific. When the dif- 

 ferences in body proportions between two samples is great, the 

 index number appearing on the above chart is large, and when the 

 tuna from the two sample areas are similar, the numbers are 

 small. This analysis shows that west coast yellowfin differ widely 

 from those of the central Pacific, and that the yellowfin of the cen- 

 tral Pacific differ considerably from those farther west toward 

 Asia. Unfortunately no one knows how large an index number is 

 requiredto prove complete separationof stocks or conversely how 

 small it should be when there is complete mixing. Firm conclu- 

 sions require evidence from other sources. 



17 



