(il'NDKRSON: POPULATION KIOLOOV MF SEHASTES ALUTUS 



TABLE 19.— Estimated 



populations based on 1 

 growth and maturity. 



population fecundity (millions of larvae released) for hypothetical 

 ,000 recruits per year, under different levels of fishing mortality 



Pacific ocean perch 

 and compensatory 



order to accommodate the changes in age at 

 maturity. It was assumed that the length-weight 

 relationships, length-fecundity relationships, and 

 vulnerability coefficients characterizing the stan- 

 dard populations would apply to the other popula- 

 tions as well. All calculations have been carried 

 out for M = 0.1 and M = 0.2. 



The results (Table 19) for standard growth when 

 F = give the estimated population fecundity for 

 the virgin stock. In actual fact, biomass was re- 

 duced below virgin stock levels several years prior 

 to the time when the "standard" rates of growth 

 were estimated and some compensatory changes 

 could already have occurred. The population 

 fecundity in the "standard" population when F = 

 could consequently overestimate preexploita- 

 tion fecundity to some degree. 



For both stocks considered, fishing mortalties 

 greater than F = 0.1 doom Pacific ocean perch to 

 lower levels of population fecundity than those 

 existing prior to exploitation. None of the popula- 

 tions examined were able to recover preexploita- 

 tion levels of population fecundity when F = 0.2, 

 even when mean length at age increased by 5% 

 and sexual maturation occurred a year earlier 

 than normal. 



Even ifF is restricted to 0. 1, the ability to regain 

 virgin stock levels of fecundity varies sharply with 

 M. IfF = M = 0.1, the results for both stocks show 

 that even if growth increases by 59c and sexual 

 maturation occurs a year earlier than normal, 

 population fecundity will be 12-13% less than in 

 the virgin stock. If M = 0.2, the outlook is better, 

 since the stocks were able to recover 92-97% of the 

 preexploitation fecundity with a 5% increase in 

 growth. 



The main point to be considered, however, is 

 that even when F = 0.1, Pacific ocean perch would 

 have to undergo significant compensatory changes 



in growth to regain virgin stock levels of popula- 

 tion fecundity and would possibly have to mature 

 a full year earlier than normal. In this light, the 

 intensive fishing of the U.S.S.R. and Japanese 

 trawl fleets in the past has been quite remote from 

 the concept of long-term equilibrium yield. 



In the case of the WVI stock, exploitation was 

 most intensive during 1967, and, depending on the 

 value of M used, 1967-68 estimates of F ( = Z - M) 

 would range from 0.36 to 0.46 (Figure 17). In al- 

 most every year since, the estimated value of F 

 would exceed 0.1, regardless of whether M = 0.1 or 

 0.2. The situation is less clear in the case of the 

 QCS stock, but mortality estimates based on the 

 age composition of the Washington trawl fleet 

 (Figure 16) indicate that F was between 0.66 and 

 0.76 during 1968-69 and exceeded 0.1 during 

 1969-72. 



Drastic action will probably be required to re- 

 turn Pacific ocean perch to their former levels of 

 population fecundity, beginning perhaps with a 

 total ban on commercial fishing, such as that pro- 

 posed by Snytko (1971). Once this has been ac- 

 complished, harvest from both the QCS and WVI 

 stocks should be regulated so that the catch does 

 not exceed 0.1 (3, where /3 is the estimated stock 

 biomass. 



SUMMARY 



Pacific ocean perch are a dominant component of 

 the fauna of the North Pacific, attaining a wide 

 geographic distribution and high levels of popula- 

 tion density prior to exploitation. Intensive exploi- 

 tation by man created a sudden change in their 

 population biology, and one that they were poorly 

 adapted to cope with. Pacific ocean perch stocks 

 lack the resilience of highly fecund, oviparous 

 groups like the gadoids and their ability to main- 



399 



