ABSTRACT 



This analysis of the size frequencies of longline-caught yellowfin tuna, Neothunnus 

 macropterus (Temminck and Schlegel), is based on weight data collected in the Honolulu market 

 from 1948 to 1953 for Hawaiian waters, and onmeasurements taken aboard research vessels from 

 1951 to 1954 for the central equatorial Pacific and aboard Japanese tuna motherships in 1950 and 

 1951 for the western equatorial Pacific. The modes which occur in the size-frequency distribu- 

 tions for these three areas are all in similar positions, but certain modal groups present in the 

 Hawaiian material are frequently or consistently missing from the central and western equatorial 

 samples. In both the Hawaiian and equatorial areas there are no important differences in the size 

 composition from year to year. 



Snnaller yellowfin (100-130 pounds) enter the Hawaiian fishery in June and July, and the 

 larger fish (over 130 pounds) appear in August and September. 



Progression of the nnodes in the Hawaiian samples indicates growth, with the rate slackening 

 in the latter half of each year. No such n-iodal progression appears in the data from equatorial 

 waters. 



Male yellowfin in Hawaiian waters attain greater size than do the females, and they usually 

 nnake up about 64 percent of the fish taken by longline. Similar sex ratios and size differences 

 between the sexes are found in the samples from equatorial areas. 



