GUNDKRSON: POPULATION BIOLOGY OF. SEBASTES Ml FUS 



fish were partitioned between two different ob- 

 servers to balance out the effects of any bias. 



The mean number of eggs per milliliter was 

 calculated for each of the 4-6 subsample means 

 from a given specimen and the coefficient of varia- 

 tion (CV = standard deviation/mean of subsample 

 counts) for these subsample means had the follow- 

 ing distribution: 



For most specimens (81% ), the standard deviation 

 of the subsample means was within 15% of the 

 grand mean. The fecundity of each specimen was 

 estimated by using the formula: F = 2,000n, 

 where F = fecundity and n = mean number of 

 eggs per milliliter in the subsamples. 



Results of Fecundity Study 



May (1967) reviewed the results of fecundity 

 work on several species (cod, Gadus morhua; her- 

 ring, Clupea harengus pallasi; long rough dab, 

 Hippoglossoides platessoides), which showed that, 

 for most practical purposes, variation in fecundity 

 is adequately explained in terms of length alone. 

 Raitt and Hall ( 1967 ) came to the same conclusion 

 in their work on the Atlantic redfish, Sebastes 

 marinus, a species belonging to the same genus as 

 Pacific ocean perch. They carried out multiple re- 

 gression of log F and logL using weight or age as 

 second independent variables, and it was found 

 that inclusion of variates other than length did not 

 significantly reduce residual variation. As a re- 

 sult, the fecundity work in the current study was 

 directed primarily toward determining the rela- 

 tion between fecundity and length. 



Fecundity data for Sebastes alutus seemed to fit 

 the relation F =aL b , where F = number of oocytes 

 in thousands, L = fork length in centimeters, and 

 a and b = constants. 



The values of a and b were determined by trans- 

 forming this equation into: logF = logo + b log L 

 and using linear regression techniques to fit logF 

 - log L data to a straight line. Data from 

 Washington-Oregon and Queen Charlotte Sound 



were treated separately, and the following results 

 were obtained: 



Washington-Oregon 

 F = (0.19295 x io-9) L 7 - 32506 

 Queen Charlotte Sound 



F = (0.12240 X 10 6) £5.51258 



Predicted fecundity at each length was calcu- 

 lated from these relationships, and is shown in 

 Figure 22. The significance of between-area dif- 

 ferences in the length-fecundity relation was 

 examined statistically, using the BMD 3R4V 4 

 computer program for analysis of covariance. The 

 results of this analysis showed that between-area 

 differences in the fecundity-length relation are 

 statistically significant at the 95% level and that 

 they are due to differences in the intercepts of the 

 logF - logL regression lines (F = 5.85 with 1,76 

 df ) rather than to differences in their slope (F = 

 3.43 with 1,75 df). 



Two workers (Westrheim 1958; Snytko 1971) 

 have previously examined the length-fecundity 

 relation for Pacific ocean perch off Washington- 

 Oregon, although neither carried out correspond- 

 ing studies for the Queen Charlotte Sound stock. 

 Westrheim's results were the first available and 

 were based on examination of 13 specimens. Wes- 

 trheim collected his fecundity samples during 

 September-November ( 1951 and 1952), estimated 



4 BMD 3RV. Regression with Analysis of Covariance. This is 

 an addition to the University of California BMD program series, 

 developed at the University of Washington Computer Center by 

 W. Farr. 



35 



36 



37 



39 40 



Length (cm) 



42 



45 



FIGURE 22.— Relation between fecundity and length for Pacific 

 ocean perch off Washington-Oregon (as determined by three 

 different workersl and in Queen Charlotte Sound. 



393 



