FISHERY BULLETIN: VOL. 75, NO. 2 



April-May 



June-Aug. 



Sept.- Dec 



Virgin |Q 

 Rocks IU 



N=2378 



FIGURE 9.— Size composition of 1966-72 Pacific ocean perch 

 catches in Queen Charlotte Sound, by fishing ground and season. 



derson 1974), and fishermen probably restrict 

 their efforts to periods of high availability. If this 

 is the case, the relative levels of monthly catch 

 give the best index of stock availability. Peak 

 availability occurs during March-April (near the 

 time of embryo release) and in August-December 

 (near the mating period). This pattern of seasonal 

 availability agrees well with results from previous 

 studies of the WVI stock (Gunderson 1971; Snytko 

 1971). 



AGE-LENGTH RELATIONSHIPS 



Queen Charlotte Sound 



The age-length relationship in any sample of 

 Pacific ocean perch from Queen Charlotte Sound is 

 influenced by the availability of large, fast- 

 growing fish, the depth at which the fish were 

 captured, and the proportion of the annual growth 

 completed. In order to examine the relative impor- 

 tance of these factors, analysis similar to that out- 

 lined by Gunderson (1974) was employed. 



This involved fitting observed mean length at 

 age data to the von Bertalanffy growth model, 



l t =L«(1 - exp-K(t - * )) 



20 

 10- 



0- 

 20- 

 10- 



0- 

 20 

 10- 



0- 

 20 

 10- 



0- 



20- 



10 



fc - 



«j 



£ 20 

 10- 





 20 

 10 





 20 

 10 





 20- 

 10- 







20 



"- 598 ,.rJ\ 1 Why, 



N = I225 



frfii-L 



J 



"W . 



tk 



jfl 



tthCL 



J 



SEP 



Trrfl^ 



urn 



OCT 



"h-TUn 



-^RTrrfrrH, 



DEC 



"■gy^mfflTTL , 



30 40 



Length (cm) 



. ^TliTTr^ 636 





N=I95 



^rMh^^» 



-AiWhuyrTW^--' 



-^iihH^Th^-^ 



jf. 



"U^-HtTU n " 



-^flTh^fTr^" 701 



30 40 50 



40 

 Length (cm) 



FIGURE 10. — Size composition in 1967-71 Pacific ocean perch 

 catches from Washington-Vancouver Island, by month. 



376 



where l t = length of fish in centimeters at t years 

 L x = theoretical asymptotic length 

 K = constant expressing the rate of ap- 

 proach to L x 

 £ = theoretical age at which I, = 0. 



The least squares technique of Tomlinson and Ab- 

 ramson (1961) was employed to do this, and a 

 separate age-length relationship was computed 

 for each combination of fishing ground and season 

 (April-May, June-August, and September- 

 December) where adequate data were available. 

 All comparisons of the age-length relationship at 

 different grounds and seasons could then be made 

 by comparing fitted length at some common age 

 (age 15 in this case). 



The results (Figure 11) show that the age-length 

 relation is more dependent on the availability of 

 fast-growing fish to bottom trawls than on any 

 other factor examined. The main line of evidence 

 supporting this is the close correspondence be- 

 tween changes in fitted length at age 15 (Figure 

 11) and seasonal changes in size composition (Fig- 

 ure 9), a situation that would be expected if both 

 depend on the availability of large, fast-growing 



