-48- 



These models were also applied to data from 

 the south Atlantic fishery. Estimates of MSY were 21,000 mt for the m=2 

 model, 25,500 mt for the m=l model, and 49,000 mt for the m=0 model (Figure 

 10). The 1978 catch was 20,500 mt at an estimated effort 3 to 41% less 

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

 approximately 20,100 mt. 



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



Yield- per- recruit analyses have been used in the past to 

 assess the status of bigeye tuna stocks, and were the basis of the size 

 limit proposal in 1979. A new analysis was performed in 1980 by ICCAT's 

 Working Group on Juvenile Tropical Tunas. Results confirmed that 

 increasing size-at-first-capture from approximately 0.9 kg (30 cm fork 

 length) to 3.2 kg (54 cm) would increase yield-per-recruit to the fishery, 

 especially at higher levels of effort (Figure 11). 



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



Recruitment to age-1 for year-classes 1967 to 1973 was 

 estimated (Figure 12). Only longline data from the total Atlantic fishery 

 were considered. Depending on the natural mortality rate chosen, estimates 

 vary moderately and no general trend is apparent. 



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

 None available. 



III.C. Current Evaluation of Stocks and the Fishery 



Results of the production model analyses indicate that Atlantic 

 bigeye tuna are currently being fished below levels corresponding to MSY. 

 All models indicate that increases in yields are available with increases 

 in effort. Until the fishery operates at higher effort levels it is 

 impossible to select the appropriate model and MSY. 



Any increase in size-at-first-capture should increase yield-per- 

 recruit to the fishery. The feasibility of increasing size-at-first- 

 capture for the baitboat fleets, however, is questionable. Since these 

 fleets take small bigeye tuna' with catches of skipjack, any increase in 

 size-at-first-capture may result in decreased skipjack catches. Continued 

 increases in catches of small bigeye should result in decreases in yield- 

 per-recruit. 



