Similar time trends in fishing effort and hatchery production, 

 combined with high intercorrelations between the most useful 

 independent variables, affect the reliability of ocean chinook 

 salmon catch predictions based on simple regressions. The 

 importance of lower Columbia River hatchery production of fall 

 chinook salmon to the fishery off Washington and southwestern 

 Vancouver Island is difficult to dispute, however, based on both 

 mark-tag recaptures and the close association between ocean 

 fishing success and this factor, as shown in this paper. Because 

 there is also some association between ocean fishing success in 

 year / and troll CPUE in the fall of year i — 1 , length data and 

 scale samples from troll-caught immature (shaker) chinook 

 salmon could improve predictions of catches in the following 

 year. Although there no longer is a fall commercial troll fishery 

 off Washington, these data could be obtained in a test fishery. 



The lack of significant association between ocean fishing 

 success for coho salmon and hatchery production, together with 

 the tendency for negative correlation, is puzzling, particularly in 

 view of the close association noted for fall chinook salmon. One 

 explanation is the masking effect resulting from the contribution 

 of several age groups to the chinook salmon fishery, whereas the 

 coho salmon fishery is dependent upon a single age group. Thus 

 the effect of abnormally high ocean mortality on a single year 

 class of hatchery-released chinook salmon is less likely to be 

 reflected in the ocean catch than is the impact of a similar 

 mortality on a year class of coho salmon releases. This 

 dependence on a single age group does facilitate prediction of 

 ocean coho salmon catches, however, when a variable (e.g., 

 upwelling or jack count) reflective of probable ocean survival is 

 included in the model. Although the pink salmon catch is also 

 obtained from a single age group, the coho salmon catch does 

 not fluctuate to the extremes observed for pink salmon. Of the 

 three species considered here, coho salmon appear to offer the 

 best prospect for reasonably accurate prediction of ocean catch. 



ACKNOWLEDGMENTS 



This study was funded by the U.S. Fish and Wildlife Service 

 under Contract No. 14-16-0008-972. Richard R. Whitney of the 

 College of Fisheries, University of Washington, reviewed an 

 early version of the manuscript and offered many valuable 

 comments. 



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