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II I. A. Stock Structure 



Little is known about the structure of Atlantic skipjack tuna 

 stocks. A separate east-west stock has been hypothesized and indeed 

 skipjack catch has been traditionally segregated into eastern and western 

 Atlantic components. Results of tagging programs in 1980 by the United 

 States in the Caribbean, the Spanish in the Canary Islands, and the 

 Japanese in the Gulf of Guinea should provide information bearing on this 

 problem. 



III.B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends- in-Catch-per-Un it-Effort 



Available skipjack tuna catch-per-unit-effort (CPUE) 

 estimates for the eastern Atlantic include those for the FISM and Tema- 

 based fleets. These estimates are dissimilar because they are based on 

 different units of effort. In addition, neither of these eastern Atlantic 

 CPUE estimates provides a valid index of abundance because skipjack 

 availability varies markedly from year to year. This problem is further 

 complicated by some vessels, including FISM fleet units, fishing skipjack 

 only in times of low yellowfin/high skipjack availability. The FISM and 

 Tema-based fleet CPUE indices, are, however, the only information available 

 for inferring skipjack abundance in the eastern Atlantic. 



The FISM estimate is considered to be the most 

 representative of the two eastern Atlantic CPUE estimates and is presented 

 in Figure 9. CPUE for 1969-1979 fluctuated between one and three metric 

 tons per fishing day, with no apparent trend over time. 



No CPUE index currently exists for the western Atlantic. 



III.B. 2. Results of Production Model Analysis 



Plots of fishing effort, catch, and CPUE from the FISM 

 purse seine fleet in the eastern Atlantic are presented in Figure 10. 

 Attempts to fit the production model to these data have failed to produce a 

 viable relation between surplus production and effort. Due to spotty 

 fishing effort and small catches in the western Atlantic (9,000 mt 

 annually), production model analysis for western Atlantic has not been 

 attempted. 



