298 



FISHERY BULLETIN OF THE FISH AND "WILDLIFE SERVICE 



2 4 6 



2 3 7 II 



NUMBER OF LARGE / SMALL SKIPJACK IN THE CATCH 



15 19 23 



Figure 14. — Size composition and the total catch in the Oaliu skipjack fishery, 1952-53. 



Group B : Nonmigratoi-y small fish, which 

 during the summer months are about 4 to 8 pounds 

 in weight. These fish occur in semi-permanent ag- 

 gregations wliich are to be found in certain locali- 

 ties, usually near shore, where presumably oceano- 

 graphic conditions are suitable for the concentra- 

 tion of food organisms. These fish, according to 

 Brock's hypothesis, are a year yomiger than the 

 season fish. This group serves as the main source 

 of supply for some of the fishermen, but in gen- 

 eral it functions as a reserve supjily where most 

 of the fishermen can use their bait, when larger 

 fish are not available. 



Group C: Large migratory skipjack, 28-32 

 pounds, which may be a year older than the season 

 fish. This group seems to have been abundant dur- 

 ing the first part of 1953 and accoimts for the ap- 

 parent early begining of the season in that year. 



Group D: Migratory small skipjack. The ex- 

 istence of this group is not well established ; how- 

 ever, the large numbers of small fish which appear 

 suddenly in the fishery in periods 14, 15, and 20 of 



1952 suggests that there may be, a migratory group 

 of small fish as well as the semiresident group. 



In figure 16, catches of large skipjack number- 

 ing in excess of 15,000 were all made when season 

 fish (group A) were apparently dominant in the 

 fishery; the large catches of small skipjack, those 

 in excess of 40,000, are presumed to result from the 

 presence of migratory small fish (groui^ D). The 

 sharp decline in the number of periods with 

 catches of small skipjack greater than 25,000 may 

 indicate that this number is about the maximum 

 number of nonmigratory fish (group B), which 

 are available during a biweekly period. Except 

 for period 17, 1953, the number of small fish in 

 the catch declines as the number of large fish in- 

 creases, which is consistent with the assumption 

 that the number of small fish caught is inversely 

 related to the availability of large fish. The extra- 

 large migratory fish (group C) are distinguished 

 by their greater average weight relative to the 

 season fish, and not, at least during 195.2-53, by 

 their unusually large numbers. At the time of 



