Polovina: Hatchery releases of juvenile Sebastes alutus 



133 



Q 



CO 



O 



X 



o 



is 



o 



LU 



> 



_! 



O 



100- 

 80 

 60 

 40 

 20 

 



100 

 80- 

 60- 

 40 

 20 



B 



10 20 30 40 



YEARS SINCE 1977 



50 



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

 n 22-50 <Q— Q) 



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

 15-50, with stocking of 5 million 

 per year for 6 years (H *-) 



Q F = 0.03, years 1-35; F = O.06, 

 u years 36-50 (n—rj) 



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

 years 17-5*0, with stocking of 5 mil- 

 lion per year for 10 years (+ h) 



Q F = 0.06, years 1-50 (Q— Q) 



F = 0.06. years 1-50, with stocking 

 of 5 million per year for 12 years 

 (+— + ) 



Figure 5 



Simulated cumulative catches of 

 Pacific ocean perch, with and with- 

 out hatchery releases, for three 

 management strategies. 



stant (Figs. 4,5). The biomass distributions with and 

 without stocking are very similar after 20 years (Fig. 

 6). 



When F = 0.03, B MSY is achieved in 35 years without 

 stocking and in 17 years when 5 million juveniles are 

 stocked annually for 10 years (Table 3). The annual 

 catches for both the stocked and nonstocked strategies 

 are the same for the first 8 years because of the 8-year 

 lag between the release of juveniles and their entry into 

 the fishery; but beginning in year 9, the annual catches 

 in the stocked strategy exceed those for the nonstocked 

 strategy. In year 16, B MSY is achieved in the stocked 

 strategy, and F is increased to 0.06, which results in 

 a substantial increase in annual catches. The annual 

 catches for the nonstocked strategy lag behind the 

 stocked catches until year 35 when B MSY is achieved 

 and F is increased to 0.06 (Fig. 4). The difference 

 between the cumulative catches for stocked and non- 

 stocked is initially very small, because the two strate- 

 gies have the same annual catches at the beginning, 

 but the difference grows once the annual catches 

 diverge (Fig. 5). After 20 years, the distribution of 

 biomass for the stocked population is about 10,000 t 

 greater than for the population without stocking (Fig. 

 6). 



When F = 0.06, B MSY is not achieved within 100 

 years without stocking, whereas B MSY is achieved in 

 20 years with stocking (Table 3). The patterns of an- 

 nual and cumulative catches for the stocked and 

 nonstocked cases are similar to the F = 0.03 situation 

 (Figs. 4,5). After 20 years, the distribution of biomass 

 without stocking shows very little change from the level 

 at the beginning of the recovery period, whereas the 

 distribution of the stocked population centers close to 

 Bmsy (Fig. 6). 



The value of stocking to increase yields while restor- 

 ing the depleted Pacific ocean perch population can be 

 evaluated by computing the break -even cost of a hatch- 

 ery-released juvenile based on the increase in cumula- 

 tive landings. Suppose a hatchery, built and operated 

 by government funds, must meet the economic cri- 

 terion of a 3% return on investment. Then the break- 

 even cost per juvenile, as a function of n years after 

 the start of stocking, can be calculated as follows: (1) 

 Compute the increase in cumulative yield between the 

 comparable stocked and nonstocked strategies, n years 



