Research Document - 2002/036
Impact of harvesting on population trends of beluga in eastern Hudson Bay
By H. Bourdages, V. Lesage, M.O. Hammill, B. de March
Abstract
Inuit people from the Nunavik have traditionally harvested beluga along the eastern Hudson Bay (EHB), Hudson Strait and Ungava coasts of northern Quebec. Quotas and other management measures exist since 1986, and are revised periodically. The current management plan and recommendations for harvest levels in the Nunavik region were established in April 2001 based on the best available data, i.e. population size in 1985 and 1993, and harvest statistics from 1974-2000. This study presents different scenarios of past and future harvests, while incorporating new information on beluga abundance in James Bay, EHB, Hudson Strait, and Ungava Bay, genetic composition of the harvests, and harvest statistics from 2001. Harvest statistics indicate that the communities of Nunavik exceed quotas each year. Both a relatively simple model using population estimates, removals and rate of increase, and a more complex model introducing additional variables on stage-specific biological parameters were used to examine the impact of harvesting on the growth of the eastern Hudson Bay beluga population. The two models yielded very similar results. They both indicated a decline in EHB beluga population since 1985, a population size in 2001 of approximately 2045 individuals (2090 vs 2001), and an underreporting of harvests prior to 1995 by a factor of 2.23-2.22.
The short- and longer-term impacts of future harvesting on the EHB beluga population were examined under different scenarios. However, the probability of decline on the short-term changed little between a harvest of 0 (48%) or 150 (56%) beluga from the EHB stock owing to the uncertainty surrounding the current estimates of population size. However, more certainty of a decline is acquired over time, and the influence of the number of removals per year is revealed more clearly over a longer time period. There is a 70-80% certainty of a decline in five or 10 years if over-harvesting practices similar to what was observed in 2001 (i.e. 125-150 EHB beluga) continue in the future. Reducing the quota to 25 beluga results in a 45% probability of a smaller stock in five years, whereas a complete cessation of EHB beluga harvesting results in a 35-40% probability that the stock will show now further decline in 5 years. Using minimum population estimates of 1657 and 1423 individuals for EHB beluga for Model 1 and 2, respectively, and a maximum annual rate of increase of 4%, the potential biological removal (PBR) is 15 individuals, assuming a recovery factor of 0.5 (for a threatened population which is not in decline). The PBR decreases to 9 beluga if this threatened population is assumed to be declining (recovery factor of 0.3), and to 3 beluga if it is considered endangered (recovery factor of 0.1).
In contrast with the EHB population, numbers of beluga in James Bay appear to have increased since 1985 to an estimated 10,504 beluga in 2001 (assuming an annual rate of increase of 0.03 to 0.04). The model fitted best the data when it was allowed to optimise the rate of increase. In this scenario, this population grew at a rate of 0.087 and was estimated to number 15,954 beluga in 2001.
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