■13- 



Some of the results of the second series of computations with new, adjusted 

 coefficients are shown in Figures 17 and 18. These two figures are directly 

 comparable to Figures 15 and 16 and to Figures 3 and h (the latter presenting 

 uncompensated biomass dynamics). Considerable decrease in the biomass of pollock 

 occurred with the new coefficients when compared to previous computations with 

 initial coefficients (Figure 17 compared to Figure 15), whereas the decrease of 

 yellowfin biomass is smaller (Figure 18 compared to Figure 16). In the latter 

 species, the biomass still increases with increasing fishing. The main reason 

 for the differences in the dynamics of biomasses in the two species is that the 

 fraction of prefishery juveniles in pollock is considerably smaller than in 

 yellowfin. In this connection it is well known from empirical observations that 

 stocks of different species respond differently to comparable (equal) fishing 

 pressure. 



The influence of fishing on the dynamics of a stock biomass is affected in 

 about equal shares by the change of stock growth rate and by the change of total 

 mortality via the change of relative contribution of spawning stress mortality. 

 The growth rate change of the stock is affected via the change of biomass 

 distribution with age, which also influences the recruitment to exploitable stock. 

 The effects of the new (adjusted) growth rates of biomass on the biomass dynamics 

 are shown in Figures 19 and 20. These figures are comparable to Figures 9 and 10, 

 which were computed with the first set of coefficients of the effects of fishing. 

 The corresponding effects of new (adjusted) spawning stress mortality coefficients 

 are shown on Figures 21 and 22, which are comparable to Figures 7 and 8, computed 

 with first set of coefficients of the effects of fishing without partial fishery 

 on prefishery juveniles, and assuming constant recruitment. 



