Research Document 2017/061

Estimated abundance of the Western Hudson Bay beluga stock from the 2015 visual and photographic aerial survey

By Matthews, C.J.D., Watt, C.A., Asselin, N.C., Dunn, J.B., Young, B.G., Montsion, L.M., Westdal, K.H., Hall, P.A., Orr, J.R., Ferguson, S.H., and Marcoux, M.

Abstract

Aerial visual and photographic surveys of summering Western Hudson Bay (WHB) beluga (Delphinapterus leucas) were conducted in August 2015 to update the previous stock abundance estimate from 2004. The survey area comprised five strata (three visual and two photographic) encompassing high use areas around three river estuaries where recurring aggregations of WHB beluga are found during the summer months. The photographic surveys completely covered high density aggregations in the Churchill River and near the mouth of the Seal River. Poor weather conditions prevented replicated surveys of all but the Churchill River photographic stratum. Near-surface abundance estimates for each stratum were adjusted for availability bias using dive data collected from eight satellite-tagged WHB belugas during the same period as the aerial survey. Belugas in rivers spent 58.3 ± 3.7 % of their time within the 0–2 m depth bin, resulting in a correction factor of 1.71 ± 0.11 for murky water, while belugas in coastal areas spent 80.9 ± 3.0 % of their time within the 0–5 m depth bin, resulting in a correction factor of 1.24 ± 0.05 for clear water. Summed corrected stratum abundance estimates provided a total stock abundance estimate of 54,473 (CV = 0.098, 95 %; CI = 44,988–65,957).

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