Research Document - 2012/159

Size and trend of the Cumberland Sound beluga whale population, 1990 to 2009

By P.R. Richard

Abstract

This document reports on the results of aerial surveys conducted in 1990, 1999 and 2009 to estimate the present size and trend of the Cumberland Sound beluga whale population. Aerial surveys of the known summer range of beluga whales in the Sound were flown in August of those three years. The results show greater numbers of belugas in 1999 than in 1990 or 2009. The 2 August 2009 surveys produced an imprecise population estimate of 788 belugas (2.5-97.5 bootstrap percentiles = 310-1,679). Comparison of population estimates for the three years of surveys appear to imply that the population changed with rates of increase or total mortality that are unrealistic. Consequently, there must be sampling error which is unaccounted for by the survey results. Several possible sources of bias are identified. Some aggregations of belugas within the surveyed areas may have been missed and part of the population could have been outside of the surveyed area and that proportion varied between survey years. Additionally, there may have been inter-annual variation in diving behaviour of belugas during surveys which would have influenced the applicability of the dive correction. Finally there may have been unmeasured differences in efficiency at detecting belugas (e.g., observer error, visibility conditions) between survey years. More surveys and a population dynamic model are required to better estimate the size of, and trend in, this small population.

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