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Fishery Bulletin 89|1), 1991 



Model results 



Short-term perspective 



Since fishing mortality has been so low in recent years 

 and the stock has increased, an attempt was made to 

 investigate the effect of further stockpiling of fish on 

 expected catches and spawning stock size. To address 

 this problem, a series of 5-year simulations were used 

 to compare the density-dependent model results with 

 projections from the standard model. Fishing mortal- 

 ity was set at 0.05, a value close to the average rate 

 over the last several years. These runs suggest that 

 advice based on the standard model would have over- 

 predicted catch by about 8% in 1987 and spawning 

 stock size in 1988 by about 13% (Fig. 5-G). Further- 

 more, if the standard model were used to project more 

 than a few years into the future, the estimate of spawn- 

 ing stock could possibly be too large; the 1991 estimate 

 would be lower by 37% for the DDM model (Fig. 5-G). 

 If the frequency of yields over this 5-year series is 

 calculated, the STD model is more optimistic with a 



mean catch of 74,892 mt versus 63,686 mt for the DDM 

 model (Fig. 7). Similarly for spawning-stock biomass 

 (SSB), the STD model suggests a higher mean SSB of 

 1.5 million mt versus 1.1 million mt for the DDM model 

 (Fig. 7). 



Since F .i is an important benchmark fishing-mor- 

 tality rate in the present management plan, another 

 5-year summary with F = 0.29 (F, u ) was also pro- 

 duced. As with the previous example, mean yield for 

 the STD model was considerably higher, 242,939 mt 

 versus 197,116 mt for the DDM model (Fig. 8). Spawn- 

 ing-stock biomass would be considerably different 

 under the two perspectives with an estimated mean 

 SSB of 1.0 million mt under the STD model and 

 725,887 mt under the DDM model (Fig. 8). 



Long-term perspective 



To develop a longer-term perspective, simulations at 

 the same two levels of fishing mortality (F = 0.05, 0.29) 

 were produced for 15-year series to allow sufficient 



