GUNDERSON: POPULATION BIOLOGY OF SERASTES ALUTUS 



1967, but a good series of data, taken over the 

 entire year, is available for each year during 

 1967-73. 



Because a limited number of samples was avail- 

 able during 1956-66, it was frequently necessary 

 to pool data from adjacent years when examining 

 temporal trends in size composition. The results 

 (Figure 12) furnish the only available estimates of 

 the size composition of Pacific ocean perch in 

 1956-66 Washington trawl landings. 



Collection of biological data was quite intensive 

 during 1967-73, and it was possible to make al- 

 lowances for the extensive seasonal changes in 

 length and sex composition that occur in Queen 

 Charlotte Sound. The Sound was treated as a 

 single geographic unit, but size composition was 

 determined separately for each of the four time 

 strata previously discussed (January-April, May, 

 June- August, and September-December). If few 

 landings were made in one of these strata, it was 

 combined with an adjacent stratum, and biological 

 data from the latter were used to represent it. 

 Table 4 shows the time strata used for each year's 

 catch data, the landings in each stratum, and the 

 amount of biological data collected. 



Males and females differ in relative abundance 

 and size composition, so they were treated sepa- 

 rately. Mean weights of males and females in each 

 time stratum were obtained by employing the 



TABLE 4. — Time strata used for analysis of 1966-73 size and 

 age composition data from Queen Charlotte Sound. Pacific 

 ocean perch catch by Washington trawlers (metric tons) and 

 amount of biological data collected in each stratum are also 

 shown. 



length-weight relation (sexes combined) reported 

 by Westrheim and Thomson ( 1971 ), together with 

 the appropriate length frequencies in that 

 stratum. The number of males and females landed 

 in each stratum could then be estimated by divid- 

 ing total pounds landed by the mean weight offish 

 in that stratum. These values were combined with 

 size composition data to obtain the number offish 

 landed by time period, sex, and size group. Pooling 

 these data by year and expressing the results in 

 terms of percent frequency yielded the results 

 shown in Figure 12. 



Substantial quantities of large Pacific ocean 

 perch were present in Queen Charlotte Sound dur- 

 ing 1956-58. Subsequent changes in size composi- 

 tion reflect changes caused by the commercial 

 fishery and by recruitment of two strong series of 

 year classes. The first series of year classes was 

 centered around the 1952 year class and included 

 the 1951-53 brood years (Westrheim et al. 1972). 

 The presence of this series first became apparent 

 in the 1960-63 landings, when the modal size was 

 35 cm — corresponding to an age of about 10 yr. The 

 1952 year class series caused the modal size to 

 move progressively toward the right during 

 1960-70 (as its members grew in length), but 

 seemed to have little influence on size composition 

 in subsequent years. This is probably the cumula- 

 tive result of large fishery removals during 1965- 

 69, when the 1952 year class would have been 

 13-17 yr old. 



A second series of strong year classes, centered 

 around the 1961 and 1962 brood years (Westrheim 

 et al. 1972) first showed up in the 1970 landings, 

 when there was a secondary mode at 34 cm. This 

 series of year classes came to dominate the land- 

 ings during 1971-73, since the abundance of older 

 fish had been drastically reduced by commercial 

 fishing. 



Washington-Vancouver Island 



Size composition data from this region were 

 more limited than data from Queen Charlotte 

 Sound and it was never possible to analyze differ- 

 ent time strata separately. All size composition 

 data were summarized by year to produce the data 

 in Figure 12. Data from 1956 to 1965 were espe- 

 cially limited and size composition data from adja- 

 cent years frequently had to be combined. This 

 was done in such a manner that direct compari- 

 sons with Queen Charlotte Sound could be made. 



Research surveys during 1965 (Westrheim 



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