! 



mean 



ln(Spawning Escapement) 



Figure 4 — Natural logs of stock-recruitment data plotted in two 

 dimensions. Dashed lines separate marginal distributions of stock 

 and recruits into equal thirds, allowing computation of conditional 

 probabilities. 



Finally, it randomly selects a smolt production level from within the se- 

 lected region of the marginal, lognormal distribution of smolts. 



The SLCM does not allow for density-dependent interactions between 

 natural fry and hatchery-released fry when Version 2 is used. 



Hatchery The number of eggs produced in the hatchery (HEGGS) is a random vari- 



Production a te drawn from a normal distribution, where the mean and variance of the 



distribution are a function of the number of females spawned in the hatch- 

 ery and the specified fecundity parameters. If hatchery egg production 

 does not meet the minimum level defined by htarget m eggcap, then addi- 

 tional eggs (from an external source) are added to the hatchery stock. The 

 number of fry produced is a binomial random variate with N = HEGGS, 

 and p = eggjry. The fraction indicated by fryplant is released as sub- 

 yearlings; those remaining are released as yearling smolts the following 

 year. The parameters, fryjsmt and hsmtjsv, determine the survival from 

 fry to yearling smolts within the hatchery and the initial survival of smolts 

 shortly following release. 



The migration of smolts from upstream rearing areas to the estuary can 

 be a critical period for many stocks. It is especially acute for those that 

 make extensive migrations. For upper Columbia and Snake River popula- 

 tions, the migration path may include up to nine mainstem hydroelectric 

 dams and associated reservoirs. Thus, there are good reasons for having a 

 separate component for the juvenile migration period (juvenile passage). 



Juvenile Passage 



11 



