Research Document - 2014/004

Impacts of a flexible Total Allowable Take system on beluga conservation in the Nunavik Marine Region

By T. Doniol-Valcroze, J.-F. Gosselin and M.O. Hammill

Abstract

Subsistence harvest of beluga whales by Nunavik communities is directed towards a mixture of several stocks, including the depleted Eastern Hudson Bay stock (EHB). The 2013 reported harvest comprised 8 beluga taken in eastern Hudson Bay, 158 in Hudson Strait and Ungava Bay in the spring and 87 in the fall, 76 near Sanikiluaq, and 10 in the Long Island/James Bay area. Harvests in Nunavik have been stable in the past five years.

We updated the EHB beluga stock model with the 2013 harvest data The model continues to suggest that the stock has been stable in recent years, with some indication of modest population growth. The 2013 abundance was estimated at 3240 individuals (95% CI 1833–5614).

At the request of the Nunavik Marine Region Wildlife Board, we assessed whether a flexible TAT system would increase the probability of decline of the EHB stock. Our simulations, using a modified version of the current EHB assessment model, show that flexible allocation of takes over 3-year management periods has little impact on the conservation of EHB beluga. Only the most unbalanced scenarios had a measurable effect on the risk of stock decline. For instance, catching the entire 3-year TAT in the first year of each management period reduced the number of EHB catches associated with a 50% probability of decrease from 62 per year to 60. In contrast, catching the entire 3-year TAT in the last year of each management period increased this number to 64, suggesting that delaying catches can be beneficial.

However, we lack information on population age structure and on the sex/age composition of the harvest. Harvesting a disproportionate amount of reproductive females in a single year, for instance, would have negative effects on the stock that cannot be anticipated by the model. Similarly, large harvests in a given year may increase the risk of removing entire family units, which could impact genetic diversity as well as the vertical transmission of migration route that is presumably the mechanism for site fidelity.

It would be beneficial to develop a more realistic model structured by age and sex, possibly using the composition of harvest samples as a proxy of population structure. Until more information is available, harvest limits under a flexible TAT system should be based on the results of the most unbalanced scenario, in which removing 180 EHB beluga in each 3-year period has a 50% probability of causing stock decline, while lower harvests would likely allow some recovery.

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