FISHERY BULLETIN VOL 77. NO, 1 



Figure 5— Number of unregulated 

 flotsam-associated sets per month by 

 area. 1963-75. 



of;^,Ayv.,-,/, ^l\ 



A 



A 



-<Y - ^^—^i'^**, '*, 



aw 



ENTIRE CYRA 



vA4MvV^ 



25i- 



20 



FLOTSAM-ASSOCIATED 



SETS 1 



UNASSOCIATED 

 SETS 



PORPOISE- 

 ASSOCIATED SETS 



J L 



-J-J L^ 



' 1963 1965 1967 1969 1971 1973 1975 



YEAR 



Figure 6.— Average yearly catch per set of yellowfin and skip- 

 jack tuna in flotsam-associated, unassociated schoolfish. and 

 porpoise-associated sets in the CYRA. 



differences between the histograms for unas- 

 sociated schoolfish sets and flotsam-associated 

 sets are a lower proportion of unsuccessful sets and 

 a higher percentage of flotsam-associated sets 

 with catches between 25 and about 60 tons. The 

 higher proportion of large flotsam-associated sets 

 is consistent with the hypothesis that flotsam 

 aggregates tuna. 



DISCUSSION 



Changes in catch rate (catch per set. Figure 6) of 

 flotsam-associated yellowfin or skipjack tuna may 

 be related to overall abundance of flotsam- 

 associated schools, technological advances such as 

 bigger nets, increased skill and knowledge of the 

 fishermen, changes of the attractability of flotsam, 

 and changes in the residence time of tuna with 

 flotsam. In order to explain the observed increase 



152 



