The initial biomasses were arbitrarily selected and the constant portions of 

 predation and fishing mortality were adjusted to be commensurate with this 

 selected initial biomass (in the present example the input biomass was ^4200 kg/km^ 

 for both species, walleye pollock (henceforth called pollock) and yellowfin sole 

 (ca 1 led yel lowf in) ) . 



The effects of fishing on the growth coefficient were initially computed with 

 values calculated theoretically (Laevastu 1983) assuming knife-edge recruitment 

 and constant juvenile biomass: 



q = q + pf (2) 



^v ^ '^ tw 



where f is the monthly fishing mortality coefficient operating on whole biomass 

 tw 



and p was: 



Pol lock, p = 0.75 



Yel lowf in, p = 0.95 

 Other runs were made with partial fishing on year classes which were not fully 

 recruited to the fishery, and with the fishing affecting juvenile biomass (i.e., 

 fishing affecting juvenile recruitment) (see Section 6). Under these conditions 

 coefficient p (from Laevastu 1983) was: 



Pollock, p = 0.35 



Yellowfin, p = 0.85 



Predation mortality (C) consists of a "constant" portion (C.) and of a biomass 



(density) dependent portion: 



C = C, + B^ ,n (3) 



k t-1 



2 



C, and n are identical in both species under study (95 kg/km and 0.02, 



respectively), as these parameters are dependent on input biomass. The biomass 

 from the previous time step (B ,) must be used because the biomass of the actual 

 time step is not available before predation mortality is computed. 



