Estimation of the 1995 Birkenhead River sockeye salmon (Oncorhynchus nerka) escapement

In 1995, the Department of Fisheries and Oceans conducted a mark-recapture study to estimate the sockeye salmon (Oncorhynchus nerka) escapement to the Birkenhead River. Sockeye were captured at two sites in the lower river; 1,862 were released with disk tags and secondary marks. The spawning grounds were surveyed through the period of spawning and die-off; 14,019 carcasses were recovered, of which 604 were marked. Analysis revealed that application was biased temporally, spatially and by sex, and that recovery was biased temporally, by sex and by size; however, because the 95% confidence intervals of the pooled Petersen estimates overlapped those of the spatially and temporally stratified estimators, it was concluded that the pooled Petersen population estimates were not seriously biased. The 1995 escapement was estimated, using the pooled Petersen estimator, at 19,838 adult males, 20,008 adult females and 3,139 jacks. Study design changes, including adjustments to the level and allocation of sampling effort, improved resurvey procedures and modified recovery procedures to improve the jack population estimate, are recommended.