■28- 



The situation with respect to changes in minimum 

 landing size is more complex. If fishermen avoid catching small fish, then 

 the benefits to the fishery as a whole will occur as predicted by the 

 yield-per-recruit model. On the other hand, if small fish continue to be 

 caught, and are discarded dead, there may be little or no increase in 

 effective size-at-first-capture, and therefore, no benefit. Available data 

 show that Japanese Tema-based baitboats apparently discarded 1,130 mt of 

 undersized yellowfin in 1977 while landing only 2,488 mt. Higher rates of 

 discarding were noted for two trips of Tema-based baitboats accompanied by 

 Ghanaian technicians in 1978 (6,660 mt) . Therefore, the actual yield-per- 

 recruit to the fishery may be less than predicted. 



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



No spawner/ recruit relationships have been defined for 

 Atlantic yellowfin tuna. Studies were conducted which analyzed recruitment 

 of yellowfin tuna to the eastern Atlantic fisheries. Estimates of 

 recruitment to age 1 in the 1965 to 1968 year-classes varied between 12 

 million and 26 million fish. The 1969 to 1972 year-classes have held 

 relatively constant at approximately 24 million fish (Figure 13). No 

 trends in recruitment are evident. 



Increased catches over the past decade do not appear to 

 have had an adverse effect on recruitment. However, the catch-per-unit- 

 effort of the longline fishery has decreased, suggesting that the spawning 

 stock has declined. In view of this trend and of the increased catches of 

 large fish by purse seiners, the size of the spawning stock and the 

 possible effect on subsequent recruitment need to be monitored. 



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

 None available. 



III.C. Current Evaluation of Stocks and the Fishery 



Regardless of the stock structure assumed, Atlantic yellowfin 

 tuna stocks are heavily fished, particularly in the eastern Atlantic. 

 Given the present geographical distribution of the fishery and pattern of 

 fishing by different gears, it is unlikely that appreciable increases in 

 yield can be achieved by increasing the amount of fishing effort. 

 Increases in total catch which have occurred in recent years are largely 

 due to the effect of geographical expansion of the area of fishing in the 

 eastern tropical Atlantic. It is not known to what extent a further 

 expansion can be achieved, or what further increases in catch might resuH 

 from such an expansion. 



