Research Document 2017/019

Abundance index of St. Lawrence Estuary beluga, Delphinapterus leucas, from aerial visual surveys flown in August 2014 and an update on reported deaths

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

Abstract

The size and trend of the St. Lawrence Estuary (SLE) beluga, Delphinapterus leucas, population is monitored using a model that integrates abundance estimates from photographic strip-transect surveys that have been conducted from 1988 to 2009 to which the number of animals detected in the Saguenay River is added as a total count. This model also integrates the number, sex and age of animals found dead, and the proportion of 0-1 year-old calves observed on aerial photos. Since 2001, a second time series of abundance indices has been developed with visual line- transect surveys. In August and September 2014, eight visual line-transect surveys were flown over the summer habitat of beluga in the SLE to produce an index of abundance. Two surveys were conducted in an adjacent downstream area to verify possible expansion of the population summer range. In 2014, abundance indices for animals at the surface in the SLE varied from 400 to 1,169 beluga, and the number of individuals counted in the Saguenay River ranged from 0 to 49. Correcting the surface estimates to account for diving animals, and adding the Saguenay counts resulted in daily abundance indices of 885 to 2,463, with a mean of 1,574 (95% CI: 1,189 to 2,021) beluga in 2014. No photographic survey was flown in 2014. The 2014 visual line-transect abundance index is the second highest of the time series of visual surveys flown since 2001. A linear regression analysis using the 36 comparable visual abundance indices from 2001 to 2014 did not show a trend over time (adjusted R² = 0.06; p = 0.08). There is no trend in the number of adult beluga carcasses reported from 1983 to 2014 with a median of 15 whales annually. Since 2008, the number of reported newborn deaths is higher than the 0 to 3 carcasses reported from 1983 to 2007, and the numbers since the last population assessment were 5 and 6 for 2013 and 2014, respectively. Different correction factors for perception and availability bias have to be applied to photographic and visual survey abundance indices to make them comparable. Until these are developed, it is not possible to use these as comparable indices in the population model. Therefore, the review completed in 2013, which used the photographic survey time series, remains the most recent and complete stock status evaluation for this population.

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