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Research Document - 2009/006

Index estimates of abundance for beluga in eastern Hudson Bay, James Bay and Ungava Bay in Summer 2008

By J-F. Gosselin, V. Lesage and M. Hammill


The management of beluga whales hunted around Nunavik relies on the estimation of abundance of summering stocks, including the endangered Ungava Bay and eastern Hudson Bay stocks. Systematic aerial line-transect surveys to estimate abundance of beluga whales were conducted in James Bay, eastern Hudson Bay and Ungava Bay from 20 July to 28 August 2008. The flights followed east-west lines with a spacing of 18.5 km in all strata except in the central portion of eastern Hudson Bay, a high coverage area where spacing was reduced by half, i.e. 9.3 km, and the stratum was surveyed twice.  A total of 279 beluga clusters was detected between perpendicular distances of 120 m to 2880 m from the track line.  The hazard-rate model (AIC = 4145.3) with a lower AIC than the half-normal model (AIC = 4156.9) fitted on the ungrouped perpendicular distance distribution provided an effective strip half width of 839 m (cv = 0.08). Abundance indices were not corrected for availability of diving animals nor for the observer perception. A total of 214 clusters with an average size of 3.99 (cv = 0.31) were detected on 4,279 km of lines in James Bay providing an abundance index of 9,292 (cv = 0.64).  A single animal was seen over the 1,246 km surveyed in the low coverage area of eastern Hudson Bay for an abundance index of 13 (cv = 1.02). A group of three animals over 82 km provided an abundance index of 15 (cv = 1.03) in the Richmond Gulf (Lac Guillaume-Delisle). There were 2.8 times more beluga whales detected on the first survey of the high coverage area of eastern Hudson Bay than on the second survey of the same area, with 107 clusters of an average size of 2.97 (cv = 0.13) and 45 groups with an average size of 2.49 (cv = 0.30) for the first and second survey, respectively. The abundance indices of 1,797 (cv = 0.27) and 657 (cv = 0.38) for the first and second surveys respectively, provided an average, weighted by effort, of 1,237 (cv = 0.46). No whales were seen in the estuaries of the Nastapoka and Little Whale rivers during coastal surveys.  The addition of the low coverage area and Richmond Gulf abundance indices to the weighted average of the two surveys in the high coverage area provided an abundance index for the whole eastern Hudson Bay of 1,265 (cv = 0.45). Beluga whales were not detected in Ungava Bay despite the 4,334 km of offshore survey lines, the coastal surveys done between transect lines and the surveys of the estuaries of the Mucalic, False, George and Koksoak Rivers. Beluga whales were also not detected during the coastal survey of the Hudson Strait from Quaqtaq to Inukjuak conducted on 27 and 28 August. This is the fifth visual systematic survey of James Bay and eastern Hudson Bay. Differences in the surface abundance indices among years and between surveys of the high coverage area of eastern Hudson Bay in 2008, illustrate the challenges to estimate the abundance of small populations with clumped distributions.

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