Research Document - 2005/011

Abundance indices of belugas in James Bay and eastern Hudson Bay in summer 2004

By Gosselin, J.F.

Abstract

Belugas harvested around Nunavik (Northern Quebec) come from different summer stocks, including the endangered Ungava Bay and eastern Hudson Bay stocks. Systematic aerial line-transect surveys were conducted in James Bay and eastern Hudson Bay from 7 August to 1 September 2004. From perpendicular truncation distances of 100 m to 1400 m from the trackline, 250 and 104 groups of belugas were detected over 5288 km and 7987 km of lines flown in James Bay and eastern Hudson Bay respectively. The hazard-rate model was used to estimate effective strip widths of 817 m (CV = 8.9%) in James Bay and 622 m (CV = 11.2%) in eastern Hudson Bay. The weighted average of the expected cluster size at maximum detection from observations with perpendicular distances and the average of clusters with no perpendicular measurement was used to provide the expected cluster size of 1.8 (CV = 18.0%) in James Bay. An average cluster size of 2.1 (CV = 12.0%) was used to estimate density and abundance in eastern Hudson Bay. Five belugas detected in the Moose River were added to the estimated number of animals at the surface in the systematic survey to provide an abundance index of 3998 (95% CI: 2379 - 6721) in James Bay. Five belugas in the Nastapoka estuary considered to have been missed during the systematic survey were added to estimated number at the surface in the offshore area to provide an index of 2045 (95% CI: 1052 - 3982) in eastern Hudson Bay. The 2004 abundance index in eastern Hudson Bay is 44% higher than in 2001, corresponding to a 12% annual increase, which is much higher that normally accepted for beluga populations. The variation between survey estimates illustrates the difficulty of estimating the abundance of small clumped populations. As well, environmental conditions (ice extent and Beaufort conditions) might have influenced the number of belugas in eastern Hudson Bay, and changes in survey protocol (reduction of altitude, delays, different observer teams) might have affected the sampling efficiency between years. Combined with evidence of whale movement between regions, the population estimation of the 2004 survey and its large uncertainty should be considered with caution when used for management purposes.

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