Research Document - 2009/009

Abundance of Eastern Hudson Bay belugas

By M.O. Hammill, M. Kingsley, V. Lesage and J.F. Gosselin

Abstract

In previous assessments a population model incorporating density-dependence as well as information on total catches has been fitted to estimates of beluga whale abundance obtained from aerial surveys. In this assessment, a simple exponential model, incorporating information on catches was also fitted to aerial survey estimates of abundance using Bayesian methods. During initial runs, both approaches gave similar results with an estimated 1985 population of 3,900 obtained using the old model, compared to an estimated 4,100 obtained using the new model. In 2008, the estimated population has declined to 3,200 and 3,000 using the old and new models respectively. It is recommended that the model fitted using Bayesian methods be used in future assessments because the current population is much reduced from pristine levels, such that the effects of density dependent factors are expected to be limited, and the Bayesian approach presents a more rigorous approach to dealing with uncertainty concerning the dynamics of this population and is based on the full multivariate posterior distribution of the parameter estimates.

Traditionally, eastern Hudson Bay beluga whales have been made up 12%, 21% and 13% of the harvests from the Belcher Islands, Hudson Strait and Ungava Bay respectively. More recent analyses suggest that the proportion of eastern Hudson Bay animals in the spring Hudson Strait harvest is less than the proportion obtained from the fall harvest. Overall, the sample proportion of eastern Hudson Bay animals has declined to 9%. No changes were made to model assumptions because the seasonal distribution of samples collected for DNA analyses did not reflect the seasonal distribution of harvesting.

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