Estimation of the 1994 Birkenhead River sockeye salmon (Oncorhynchus nerka) escapement

The current report is the first published documentation of the Birkenhead River sockeye salmon, Oncorhynchus nerka, escapement estimation study since 1951. The report documents the study design, field methods, analytic techniques and results of the 1994 study. The Birkenhead River supports a major sockeye salmon stock which shows little evidence of cyclic dominance; escapements have exceeded 25,000 almost every year since 1940. Sockeye were captured while migrating through the river at a site near the lower limit of spawning; 1,808 were released with disk tags. Included are estimates of the 1994 age and length of adult males, females and jacks, escapement by sex and age, and average fecundity for the Birkenhead River population. The report identifies biases in the tag application and carcass recovery samples and discusses their potential impact on the population estimates. It concludes with recommendations for the improvement of study design, including improved allocation of sampling effort, resurvey procedures and the assessment of disk tag loss and handling stress.