Research Document - 2011/119

Information on abundance and harvest of eastern Hudson Bay beluga (Delphinapterus leucas)

By T. Doniol-Valcroze, M.O. Hammill, and V. Lesage

Abstract

Subsistence harvest of beluga whales by Nunavik communities is directed towards a mixture of two summer stocks: the Western Hudson Bay stock (WHB) and the depleted Eastern Hudson Bay stock (EHB). According to harvest statistics, the 2011 hunt consisted of 32 beluga killed near Sanikiluaq (Belcher Islands), 19 in the eastern Hudson Bay, 17 in Ungava Bay, 115 in Hudson Strait in the spring and 86 in the fall. Since 2009, it has been assumed based on genetic data that all animals killed in EHB, 10% of those killed in the spring and summer in Hudson Strait, and 20% of those killed in Ungava Bay and during the fall in Hudson Strait are EHB beluga. It has also been assumed that 12% of beluga killed by Sanikiluaq hunters belong to the EHB stock. Using these proportions, the 2011 harvest was equivalent to 55 EHB beluga, 5 beluga more than prescribed by the management plan.

A population model incorporating updated information on harvest statistics and stock composition was fitted to aerial survey estimates using Bayesian methods. The model estimated that the stock size in 1985 was 4,121 animals with a 95% Credible Interval (CI) of 2,225–8,857. The lowest abundance point occurred in 2001 and was estimated at 2,981 (95% CI 1,963–4,681). The model estimated a 2011 abundance of 3,030 individuals (95% CI 1,256–6535). At current harvest levels, the stock has probably remained stable over the last few years. The model estimated struck-and-loss at 56% (95% CI 22–143%) and growth rate at 2.6% per year (95% CI -3.2% to +8.5%).

To achieve a 50% probability of increase in stock abundance, future harvests should not exceed 49 EHB beluga per year, while lower harvests would likely allow some recovery. Limiting the harvest of EHB animals to 10 individuals would reduce the probability of decline to 25%. Conversely, a harvest of 103 EHB whales would have a 75% probability of leading to a decline. The probability of decline in absence of harvest is 19%. However, the number of animals that can be harvested without causing a decline of the EHB beluga stock will depend on how catches are distributed between Eastern Hudson Bay, Ungava Bay and Hudson Strait, as well as the proportion of spring/summer vs. fall catches in Hudson Strait.

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