(H'NI)KRSON POPULATION BIOLOGY OF SEBASTES ALUTUS 



The estimate of M obtained for the WVI stock 

 agrees well with an estimate obtained by Chikuni 

 (1975). Chikuni used CPUE and age composition 

 data from the Japanese trawl fleet, and estimated 

 M to be 0.227 for Pacific ocean perch in the 

 Oregon-British Columbia region. 



The general applicability of the Z - qf + M 

 model for both the QCS and WVI stocks was 

 encouraging and suggests that further collection 

 of data on mortality rates should give increasingly 

 more reliable estimates of M. At present, how- 

 ever, it probably is unwise to overemphasize the 

 between-stock differences found in natural mor- 

 tality. The results of the current study should be 

 regarded as somewhat tentative and serve mainly 

 to show that M in the Washington-Queen Char- 

 lotte Sound region lies in the range between 0.1 

 and 0.2. 



SEXUAL MATURATION 



Maturity Criteria Used 



Seasonal changes in the gross morphology of 

 Pacific ocean perch gonads have previously been 

 used to describe the reproductive cycle in the 

 Washington-Queen Charlotte Sound region 

 (Gunderson 1971; Snytko 1971). This technique 

 was again employed in this study, and, during 

 1968-73, 9,548 mature fish were classified as to 

 maturity state using the criteria in Table 9. 



Mating and insemination activities cause a re- 

 duction in the proportion of males whose gonads 

 are swollen with sperm (Stage 3), and seem to 

 occur during August-September in both the QCS 

 and WVI stocks (Table 10). About 3 mo pass before 



TABLE 9. — Description of the stages used to describe Pacific 

 ocean perch maturity. 



ovulation and fertilization of eggs occur, and this 

 is first detectable when females in maturity Stage 

 4 are encountered. Embryonic development be- 

 gins after fertilization and continues for about 2 

 mo before embryos are released. 



The peak of the embryo-release period occurs 

 during March in the WVI stock (Table 10). Most of 

 the females examined in February were in the 

 "fertilized" stage (Stage 4), while most of those 

 examined during April were in the "resting" stage 

 (Stage 7). Few observations could be made for QCS 

 females during February-April, but the results 

 suggest that embryo release occurs near March. 

 The relatively high proportion of recently spent 

 fish (Stage 6) encountered during May suggests 

 that spawning occurs somewhat later in Queen 

 Charlotte Sound than it does off Washington and 

 southwest Vancouver Island. 



Age and size at first maturity should be deter- 

 mined during the period when mature gonads are 

 most fully developed, near August-September for 

 males and near March for females. The central 

 problem in determining length or age at maturity 

 is the status of "maturing" fish (Table 9), and 

 further work was carried out to determine 

 whether or not these fish are sexually mature. Two 

 hundred sixteen fish covering a broad range of 

 lengths were selected, from the 1971-72 commer- 

 cial landings for this purpose. The length (cen- 

 timeters), sex, and weight (decigrams) of each fish 

 were determined, and the gonads classified as to 

 maturity state. The gonads were then removed 

 from the fish and weighed to the nearest 0.01 g. 

 The results ( Figure 18) were expressed in terms of 

 relative gonad weight (g), where 



g 



gonad weight (grams) 

 body weight (grams) 



x 10 2 



i.e.; gonad weight expressed as a percentage of 

 body weight. 



Males 



Between-season comparisons show that the re- 

 lative gonad weights of "maturing" males are vir- 

 tually the same during the mating season 

 (August-September) as they are during March, 

 when all male gonads are in a quiescent state. 

 These fish are obviously immature and seasonal 

 changes in their relative gonad weight contrast 

 sharply with those of adult fish. Fish classified as 

 "maturing" should therefore be grouped with 



385 



