Research Document 2017/067

Indices of abundance for beluga (Delphinapterus leucas) in James Bay and eastern Hudson Bay in summer 2015

By Gosselin, J.-F., Hammill, M.O., and Mosnier, A.

Abstract

Systematic aerial line-transect surveys were conducted in James Bay and eastern Hudson Bay from 29 July to 3 September 2015. An area of high coverage was surveyed twice in eastern Hudson Bay. Delays due to weather prevented a survey of Ungava Bay. A total of 324 groups of belugas were detected, but only 307 groups remained after the truncation of groups closer than 143 m from the track line to account for reduction of probability of detection near and under the plane (re. left truncation). A single hazard rate was selected over the half normal to estimate the probability of detection from the ungrouped distribution of perpendicular distances to provide an effective strip half width of 764 m (CV = 0.05). A total of 202 groups with an average size of 2.14 (CV = 0.10) were detected over 4,251 km of survey lines in James Bay to provide a surface abundance index of 5,074 (95% CI: 3,354-7,676). On the first and second survey of the high coverage area of eastern Hudson Bay, 58 and 63 groups with average sizes of 6.34 (CV = 0.51) and 1.41 (CV = 0.13) were detected over 7,834 km and 4,655 km of transects to provide respective surface abundance indices of 2,222 (95% CI: 816 - 6.053) and 909 (95% CI: 568 - 1,454). An individual detected over 975 km of survey lines in the northern lower coverage stratum in eastern Hudson Bay provided a surface abundance index of 13 (95% CI: 1 -127). Using a factor of 0.478 (CV = 0.16) to account for the proportion of belugas visible at the surface and adding in a count of 167 belugas observed in the Little Whale River estuary, resulted in corrected abundance indices of 10,615 (95% CI: 6,559 - 17,178) for James Bay and 3,819 (95% CI: 1,664 - 8,765) for eastern Hudson Bay. Two groups of 68 and 177 individuals that accounted for 67% of the belugas detected during the first survey of eastern Hudson Bay illustrate how the highly clumped distribution of belugas may influence abundance indices and population trend assessments.

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