Research Document - 2003/108

Abundance of Atlantic salmon (Salmo salar) in the Stewiacke River, NS, from 1965 to 2002

By Jamie, A., Gibson, F. and Amiro P.G.

Abstract

Atlantic salmon of the Stewiacke River, NS, are a part of a larger population assemblage, known as “inner Bay of Fundy Atlantic salmon” that were designated “endangered” by COSEWIC in 2001. Data for Stewiacke River salmon consist of catcheffort data from the recreational fishery (27 years), estimates of juvenile densities obtained by electrofishing (23 years), an index of adult abundance obtained by electrofishing by boat (10 years) and counts of adults bypassing a fence (4 years). Our purpose here is to use the data to estimate the number of adult salmon returning to the Stewiacke River from 1965 to 2001. We used maximum likelihood to model the catch-effort, juvenile electrofishing, adult electrofishing and fence count data to obtain estimates of the annual spawning run size during this time period. Results indicate a population size in the range of 1,100 to 6,700 during the late 1960's and early 1970's. Maximum likelihood estimates of the number of fish in the spawning run did not exceed 50 during the last 5 years, and are less than 10 since 1999. Markov chain Monte Carlo methods were used to derive Bayesian posterior distributions for the model parameters. The analyses indicate a 90% probability that the population has declined by more than 99.6% during the last 30 years and by more than 92% since the early 1990's. During the last 11 years, the estimated population size was less than during the preceding year in all but 4 years.

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