■]k- 



The mature population (spawning biomass) releases about 9 percent of its 



biomass as "sex products" (eggs and milt) each year. Fishing changes the size 



of the spawning biomass, and consequently the total amount of "sex products" 



released changes also. The biomass decreases by the amount of "sex products" 



which are released. Furthermore, the larval recruitment is affected by the 



amount of eggs deposited and could also change the recruitment to exploitable 



part of the biomass in later years. These possible effects on biomass dynamics 



were tested in the third series of computer runs, assuming relatively conservative 



relations between the spawning biomass change due to fishing and recruitment 



of the juven i les : 



D = (1 - (E /E )) •■' 0.09 (10) 



t o 



B^ = B^ - (B^ ■-'^ D) (11) 



where D is a "change factor", being a function of the quotient between actual 



exploitable biomass as affected by fishing (E ) and exploitable biomass in an 



unfished population (E ) . B^ is the actual biomass. 

 ^ o t 



The above formulas (10 and 11) should not be considered as expressing 

 explicitly any changes of recruitment per se , but only biomass change due to 

 changes in sex product release. 



The results of the computations with this "change factor" and with the adjusted 

 (new) spawning stress mortality and growth coefficients are shown in Figures 23 

 and 2h . These figures are directly comparable to Figures 17 and 18, showing 

 that the effect of the adjustment on pollock biomass is small, whereas it is 

 noticeably larger on yellowfin biomass. The reason for this species specific 

 difference is that the fraction of exploitable biomass is considerably larger in 

 pollock than in yellowfin, and consequently, fishing changes the quotient (E /E ) 



