132 



Fishery Bulletin 89(1), 1991 



(0 



O 



Figure 3 



Equilibrium yield curve (10 3 metric tons) for Pacific ocean 

 perch from Queen Charlotte Sound estimated from the Deriso- 

 Schnute model. 



F = 0.06. The second approach to stock recovery is to 

 eventually achieve B MSY while also maximizing the 

 yield to the fishery. Under this approach, the stock is 

 fished at F = 0.06 from the beginning. A third strategy, 

 which represents a compromise between these two 

 philosophies, will set F at 0.03 until the biomass reaches 

 35,000 t, then the stock will be fished at F = 0.06. 



Each of these three sequences of F can be evaluated 

 with and without hatchery releases. Catch and biomass 

 series with and without hatchery releases for each 

 sequence of F can be simulated with the stochastic 

 Deriso-Schnute model with the parameters used to fit 

 the population decline. When hatchery releases are 

 used, 5 million 1 -year-old juveniles will be stocked an- 

 nually. This number represents almost four times the 

 natural recruitment for the stock at the 1977 depleted 

 level and about 40% more than the natural recruitment 

 at the B MSY level. The variance of the random variable 

 z in the stochastic recruitment component is assumed 

 to have a variance of 0.3 (Archibald et al. 1983). Based 

 on 100 simulations of each of the six management ap- 

 proaches over 100 years, the mean annual catches, 

 mean cumulative catches and the biomass distributions 

 after 20 years can be computed (Figs. 4-6, Table 3). 



When the management strategy closes the stock 

 to fishing to restore it as quickly as possible, B MSY 

 (35,000 1) is achieved in 21 years without stocking and 

 14 years if 5 million juveniles are stocked annually for 

 6 years (Table 3). After 20 years, the mean biomass 

 levels are about the same for the stocked and non- 

 stocked cases, so annual catches are about the same 

 and the difference in cumulative yield remains con- 



1 ' [ i ' ' ' ' i ' ' ! ' i ' ' ' ' i ' ' ' ' i ' ' ' ' i ' ' " i ' ' ' ' i ' ' 



5 10 15 20 25 30 35 40 45 



YEARS 



A F = 0, y-ars 1-21; F = 0.06, years 

 " 22-50 ('0— a) 



F = 0, years 1-14; F = 0.06, years 

 15-50, wnlh slocking of 5 million 

 per year for 6 years (H >■) 



□ F = 0.03. years 1-35; F = 0.06, 

 D years 36-5'0 (fj— Q) 



F = 0.03. years 1-16; F = 0.06, 

 years 17-50, »ilh slockini; of 5 mil- 

 lion per year for 10 years ( + y-) 



C F = 0.06, years 1-50 (Q — D) 



F = 0.06. years 1-50, with stocking 

 of 5 million per year for 12 years 

 (+— +) 



Figure 4 



Simulated annual catches of Pacific ocean perch, with and 

 without hatchery releases, for three management strategies. 



