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III. B. Stock Assessment and Fishery Evaluation 



III.B.l. Trends in Catch-per-Um't-Effort 



Annual bigeye tuna hook rates were estimated from 

 Japanese longline fleet catch/effort data (Figure 7). Hook rates in both 

 the northern and southern Atlantic exhibit similar gradually decreasing 

 trends except for differences in peak hook rate years. Hook rates peaked 

 in 1974 in the northern Atlantic and 1969 in the southern Atlantic. 



No reliable CPUE estimates are available for surface 

 fisheries. 



III.B.2. Results of Production Model Analysis 



The logistic (m=2), the Gompertz (m approaches 1), and 

 the asymptotic (m=0) production models have been used to assess the status 

 of Atlantic bigeye tuna. Because division of the stocks is uncertain, 

 analyses have been performed under hypotheses of a single Atlantic stock 

 and separate north and south Atlantic stocks. 



III.B.2. a. Total Atlantic stock 



The latest available analysis utilized data 

 for the total Atlantic fishery for the period 1961-1978 (Figure 8). 

 Estimates of equilibrium maximum sustainable yield (MSY) ranged from 

 51,900 mt to 60,100 mt for m=2 and m=l models, respectively. The m=0 model 

 gave an MSY estimate of 123,200 mt. Objective criteria fail to indicate 

 any of the three models as best. The 1978 catch was 45,700 mt. The 1978 

 estimated effective effort was 25% to 50°^ less than the optimum effort (f*) 

 corresponding to MSY for the m=2 and m=l models, respectively. Optimum 

 effort for the m=0 model is undefined. The 1979 catch was approximately 

 42,000 mt. Mo estimate of effective effort is available for 1979. 



III.B.2.b. Separate north and south 

 Atlantic stocks 



Bigeye tuna fishery data were separated into 

 northern and southern fisheries and production models fit to each data set. 

 The models were applied to data .representing the northern fishery for the 

 period 1961-1978. Estimates of MSY were 35,200 mt for the m-2 model, 

 41,100 mt for the m-1, 89,600 mt for the m=0 model (Figure 9). The 1978 

 catch was 25,200 mt at an estimated effective effort 45% to 64% less than 

 f* for the m=2 and m=l models, respectively. The 1979 catch was 

 approximately 22,100 mt. 



