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III. B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends in Catch-per-Unit-Effort 



Annual indices of abundance based on catch per 1,000 

 hooks by longliners based at Pago Pago and adjusted for changes in spatial 

 distribution of nominal fishing effort (Wetherall et al . 1979; see footnote 

 1) show a fairly steady decline in catch-per-unit-effort from the beginning 

 of the index period in 1962 to 1974 (Table 4). Since 1975 the catch-per- 

 unit-effort has steadily increased. 



III.B.2. Results of Production Model Analysis 



The most recent production model analysis of the South 

 Pacific albacore fishery was based on the abundance index and effective 

 effort statistics displayed in Table 4 (Wetherall et al . 1979; see footnote 

 1). The Gull and procedure for approximating equilibrium effort was used. 

 The results, shown in Figure 5, suggest that further expansion of the 

 longline fishery would be unproductive. Indeed, it may be possible to 

 reduce effort substantially with little reduction in catch. The MSY 

 (maximum sustainable yield) of the longline fishery was estimated to be 

 about 35,000 mt. 



III.B.3. Results of Yield-per-Recruit Analysis 



No cohort analyses have been attempted with South Pacific 

 albacore due to the extreme difficulty of separating year-classes in the 

 longline catch. Furthermore, no yield-per-recruit analysis has been done, 

 in the usual sense, but a simulation model linking a yield-per-recruit 

 model with alternative stock-recruitment hypotheses has been explored (see 

 Section III.B.5). 



III.B.4. Results of Spawner/Recruitment Analyses 



No analysis of the spawner-recruit process has been done, 

 nor are data available which would permit such a study. Wetherall et al . 

 (see footnote 1) estimated the average recruitment of 2 year-old albacore 

 to be 8.4 million fish. Average spawning stock (fish over 5 years old) 

 corresponding to this average recruitment, in the absence of fishing and 

 with growth and natural mortality rates as given by Wetherall et al . , is 

 about 130,000 mt (see Section III.B.5). 



III.B.5. Results of Other Analyses/Simulations 



An age- structured simulation model was constructed by 

 Wetherall et al . to study the response of maximum sustainable yield of the 



