Polovina: Hatchery releases of juvenile Sebastes alutus 



135 



Table 5 



Contribution of juvenile releases of Pacific ocean perch to 

 biomass and cumulative yield 20 years after the start of 

 releases. 



C: 



F = 0, years 1-21; F = 0.06, years 22-50 vs. F = 0, years 

 1-14; F = 0.06, years 15-50, with 5 million juvenile re- 

 leases for 6 years. 



F = 0.03, years 1-35; F = 0.06, years 36-50 vs. F = 0.03, 

 years 17-50, with 5 million juvenile releases for 10 years. 

 F = 0.06 vs. F = 0.06, with 5 million juvenile releases for 

 12 years. 



F = 0.04 vs. F = 0.04, with 5 million juvenile releases for 

 12 years. 



F = 0.08 vs. F = 0.08, with 5 million juvenile releases for 

 12 years. 



M = 0.1 instead of M = 0.05 and strategy C. 

 F = 0.08 vs. F = 0.08, with 5 million juvenile releases for 

 3 years with growth, mortality, and Cushing recruitment 

 model (parameter estimates are from Ito et al. 1987). 

 F = 0.04 vs. F = 0.04, with 5 million juvenile releases for 

 5 years with growth, mortality, and Cushing recruitment 

 model (parameter estimates are from Ito et al. 1987). 



Discussion 



The Beverton and Holt (1966) model provides a sim- 

 ple means of evaluating the equilibrium contribution 

 of a long-term hatchery release program to the fishery. 

 The model shows that if M/K is 0.5 for the hatchery- 

 released juveniles from the time of release to capture 

 in the fishery, and if the cost of each released juvenile 

 is less than US$0.16, its value to the fishery exceeds 

 its cost. The length-at-entry for fish in these analyses 

 is assumed to be the length that maximizes the yield- 

 per-recruit, that is, 45-86% of the asymptotic length. 

 If the length-at-entry to the fishery is below this level, 

 as with some long-lived, slow-growing fishes, the con- 

 tribution of the hatchery releases to the fishery will be 

 less than the value calculated by the model. However, 

 the yield-per-recruit surface is relatively flat, so unless 

 the length-at-entry is widely different from the op- 

 timum length, the reduction in the contribution of the 

 hatchery releases should not exceed 10-15% of the 



