Research Document - 2003/017

Estimation of mean annual natural mortality for adult male snow crab Chionoecetes opilioin the southern Gulf of St. Lawrence

By Wade, E., Surette, T., Apaloo, J. and Moriyasu, M.

Abstract

A population of snow crab (Chionoecetes opilio). In the southern Gulf of St. Lawrence was monitored over a period of 15 years (1988-2002) using a series of trawl surveys. Historically, the estimates of legal sized adult males from these fall surveys were projected as the available fishable biomass the following spring fishing season, assuming that the mortality rate was zero. Using delay-difference models, we estimate the mean annual instantaneous natural mortality rate using three statistical approaches: Non-linear least squares regression (NLLS), simulation/NLLS, and bayesian analysis. To reduce possible bias in the estimation of the natural mortality rate, catchability coefficients and migration coefficients are added to the model. Estimates for mean annual instantaneous mortality rates (M) ranged from 0.26 to 0.48.

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