Modèle de population intégré pour le stock de bélugas des îles Belcher et de l'est de la baie d'Hudson (BEL-EBH)

Abstract

The Belcher Islands Eastern Hudson Bay (BEL-EHB) beluga stock is one of eight stocks found in Canada. It is one of the least abundant, with Eastern Hudson Bay beluga being currently designated as Threatened by COSEWIC. The BEL-EHB stock is harvested for subsistence by Nunavik communities and the Nunavut community of Sanikiluaq. Population models are used to estimate the population abundance and trend of the BEL-EHB stock, and to provide scientific advice on harvest levels compatible with identified management objectives. The BEL-EHB stock was last assessed using a stochastic Bayesian surplus-production model (SPM) incorporating information on harvest numbers, genetic-based composition of the harvest and aerial survey estimates. Several additional sources of information have now become available and can be used to produce a more comprehensive assessment of the stock. Here, we developed a new Integrated Population Model (IPM) for BEL-EHB beluga that integrates female reproductive status, as well as harvest sex and age composition as additional sources of information into the model structure. In addition, annual stochasticity was incorporated in the IPM as a component of mortality in addition to harvesting. We present the structure of the newly developed IPM and then compare the modeled population trends and abundance estimates to those from the SPM used in previous assessments. The IPM and SPM predicted similar overall population abundances and trends. However, uncertainties in model-based predictions were reduced with the IPM, and the most recent estimates of abundance diverged between modeling approaches. The IPM predicted that the BEL-EHB stock abundance was 3,600 in 2023, with a rate of decline between 2014-2023 corresponding to 2.24%. The 2023 estimate of BEL-EHB abundance using the SPM was 2,600 and the rate of decline between 2014-2023 was 3.82%. Both models yielded similar predictions of BEL-EHB beluga landings and carrying capacity. The IPM provided new information about the BEL-EHB stock that could not be obtained with the SPM. For instance, the IPM yielded insights into age-specific survival and pregnancy rates, as well as temporal trends in those demographic rates. Further, the IPM estimated that mortality resulting from harvest (including struck and lost) accounts for 19% to 43% of total annual mortality, with an increasing trend in recent years.