Since the successful interpretation of growth from time series 

 of size frequency distributions depends on an objective and realistic 

 nnethod of locating modes, the following criteria were adopted: 



1. No modes have been sought in distributions containing leas 

 than 100 fish. 



2. Each mode must be separated from every other mode by 

 troughs dipping at least 5 fish below modes after smoothing, 



3. Each mode must be present in the data for at least two not 

 too widely separated months. 



4. At least two of the groups making up the mode must have no 

 less than 15 individuals each before smoothing, or at least 

 10 individuals if the modal peak is present in two adjacent 

 months. 



5. The mode must be the center group of a peak of the 

 smoothed distribution or the center group of two or more 

 minor peaks which differ by less than 5 fish in height. 



SIZE DIFFERENCE BY AREAS 



Bigeye tuna taken on commercial longline gear are smaller in 

 the western than in the central Pacific (Kamimura and Honma 1953, 

 Murphy and Shomura 1953b, and Murphy and Otsu 1954). In their re- 

 port. Murphy and Shomura state that longline fishing west of 180 

 longitude yielded bigeye that averaged about 40 pounds lighter in 

 weight than those taken between 180 and 120 W. longitude. This in- 

 teresting phenomenon is believed by them to be related to ecological 

 conditions, however, Iversen-^ points out that this type of size segre- 

 gation can be the result of migration. 



SEXUAL DIFFERENCE IN CATCH 



The bigeye males achieve a larger average size than the fe- 

 males, for all recognizable male modes are to the right of the corres- 

 ponding female modes. Size distributions from the Hawaiian Islands 

 (fig. 1) and the western Pacific (137 - 165 E. longitude) (fig. 2) show a 

 parallel size differential between the sexes. 



_ 



— MS. Size variation of central and western Pacific yellowfin 

 with age and area. 



