FISHERY BULLETIN: VOL. 75, NO. 2 



TABLE 8. — Calculation of total international fishing effort for Pacific ocean 

 perch in Queen Charlotte Sound and the INPFC Vancouver area. 



09 



68-69 



tible to fluctuations that have no relation to abun- 

 dance. Fluctuations of this nature were responsi- 

 ble for much of the variability in Figure 16 and 

 resulted in negative mortality estimates for 

 1972-73. The low quality of the data on interna- 

 tional catch (especially U.S.S.R. data) also con- 

 tributed to this variability, however. 



Linear regression was carried out for the data in 

 Figure 16, and the resulting estimates of M and q 

 were 0.065 and 0.00002, respectively. As expected, 

 correlation between Z and f was quite low (r = 

 0.30). 



Washington-Vancouver Island 



Calculation of international effort in the INPFC 

 Vancouver Area is outlined in Table 8. The data 

 sources used to estimate total international effort 

 are the same as for Queen Charlotte Sound. 



Annual estimates ofZ are plotted against mean 

 international effort in Figure 17. Research cruises 

 off Washington (Gunderson 1974) have shown 

 that extreme fluctuations in the availability of 

 Pacific ocean perch occur here and that changes in 

 the age composition of the catch seem to be as- 

 sociated with them. As in Queen Charlotte Sound, 

 these changes in availability, together with the 

 low quality of the international effort data, gener- 

 ate a high degree of variability in the relation 

 between Z and/1 Correlation between these vari- 

 ables was higher than in Queen Charlotte Sound 

 (r = 0.49), however, and the data seemed to con- 



-0 2 



-03- 



IOjOOO 



20,000 

 Fishing effort (hrs) 



30POO 



FIGURE 16. — Relation between total instantaneous mortality 

 rate (Z) and fishing effort for the QCS stock of Pacific ocean 

 perch, based on data from the Washington trawl fleet. 



10,000 20,000 30,000 



Fishing effort (hrs) 



40,000 



FIGURE 17. — Relation between total instantaneous mortality 

 rate (Z) and fishing effort for the WVI stock of Pacific ocean 

 perch, based on data from the Washington trawl fleet. 



form more closely to the model proposed. Linear 

 regression analysis resulted in estimates of M = 

 0.232 and q = 0.00001 for the WVI stock. 



384 



