42 DAHLBERG 



The calculations required the assumption that entrainment is 

 randomly exploiting the larval population, i.e., all larvae have an 

 equal chance of being entrained. Number of larvae entrained (Nl) is 



Nl= f diVi (1) 



i=l 



where d, is average number of larvae during the ith sample period and 

 Vj is the corresponding volume of cooling water (Hackney, 1977). 

 Calculated on a daily basis, Nl is 2.26 x 10^ in the unstocked 

 population and 12.08 x 10*^ in the augmented population. 



Sizes of the exploited larval populations (Fig. 1) were calculated 

 from reductions in population size: 



Lp-^x 100 (2) 



where Lp is percent reduction of larval population, Vi is volume of 

 water entrained (5.45 x 10'' mVday), and V is volume of occupied 

 water (971 x 10^ m^). Thus Lp is 0.5613%/day and 22.45% in 

 40 days. 



EQUIVALENT-ADULTS MODEL 



The equivalent-adults model was proposed by Horst (1975) to 

 provide a simple first approximation of fish egg and larval entrain- 

 ment impact in terms of potential adult loss. The basic approach is 

 multiplying numbers of eggs and larvae entrained by egg and 

 larva-to -adult survival rates to estimate the number of equivalent 

 adults. The following assumptions, summarized from Horst (1977a), 

 are made when this model is applied to larval entrainment: 



1. The population is in equilibrium and has a stable age 

 distribution. 



2. Lifetime of a fish is the average age or mean generation time. 



3. Numbers of males and females are equal. 



4. Entrainment of larvae occurs at the time of hatching. 



5. The calculated equivalent adults are distributed in proportion 

 to the stable age distribution of adults. 



Horst (1975) proposed the formula 



Na=NlSla (3) 



