■23- 



(130,000 mt) is within the range of MSY estimates and is at an effort level 

 of 68,000 SDA. 



III.B.2.b. Separate eastern and western 

 Atlantic stocks 



Production model analyses were performed 

 assuming separate east and west stocks. The models were applied to two 

 eastern Atlantic data sets: 1) data from the surface and longline fishery, 

 and 2) data from the surface fishery only. 



The m = model best fits data sets 1 and 

 2 where r^ = 0.990 and 0.972, respectively. Results suggest that MSY is 

 between 94,000 and 133,000 mt, depending on the model and data set chosen 

 (Figures 9 and 10). Optimum effort is 43,000 to 46,000 SDA for the m = 2 

 model, and 49,000 to 52,000 SDA for the m = 1 model. The 1979 catch is 

 116,300 mt for data set 1 and 109,500 mt for data set 2. Current fishing 

 effort levels are 13 to 24% greater than f*. 



o 



As with the total Atlantic stock data, r'- 

 values for the m = 1 and m = 2 models were only slightly different than for 

 the m = model. Therefore, MSY estimates are presented for all three 

 models because objective criteria for choosing among the different models 

 are unavailable. If m = 1 or m = 2 is true, and the fishery is currently 

 operating under equilibrium conditions, then any increase in effective 

 fishing effort will not result in any notable increase in sustained yield. 

 If m = is true, however, increases in effective fishing effort can result 

 in increased sustained yield and decreased CPUE. 



The models were fitted to data from the 

 longline fishery in the western Atlantic. Results give MSY values ranging 

 from 16,000 mt to 22,000 mt at effort levels of 25 million and 35 million 

 hooks (Figure 11) for the m = 1 and m = 2 models, respectively. Current 

 catches are at or below MSY and current levels of fishing effort are above 

 those giving MSY. The results suggest that total catch by the longline 

 fishery in the western Atlantic will not increase with increased fishing 

 effort. 



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



Yield-per-recruit analyses performed on the 

 hypothesized eastern Atlantic stock indicate that increases in yield-per- 

 recruit to the fishery as a whole can be obtained with an increase in size- 

 at-first-capture or a moderate increase in fishing effort (Figure 12). The 

 outcome is different for the different gears: the longline fishery would 

 gain in yield-per-recruit by any increase in size-at- first-capture up to 

 about 120 cm; the purse seine fishery would gain by any increase in size- 

 at-first-capture. 



