Science Advisory Report 2017/015

An update of beluga (Delphinapterus leucas) abundance and reported deaths in the St. Lawrence River Estuary

Summary

• The beluga is an Arctic species, and the St. Lawrence Estuary (SLE) population is at the southernmost limit of the species distribution. It occurs primarily in the SLE and seasonally in the Gulf of St. Lawrence. Its current range is about 65% of the extent used historically, whereas the size of its annual core distribution is at the lower limit of areas of occupancy described for any population of this species.
• The SLE population of beluga is listed as Threatened under the Canadian Species at Risk Act (SARA) since 2005, and was designated Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 2014. Their Critical Habitat has been identified, and corresponds to the summer area occupied by females accompanied by calves and juveniles.
• Eight visual line-transect surveys were flown during August and September 2014 to estimate beluga abundance in the SLE. Surface abundance indices varied from 400 to 1,169 between surveys, with a mean estimate of 738 animals.
• Adjusting the surface abundance indices for animals below the surface while the plane passed overhead (re. availability bias) and adding counts in the Saguenay River resulted in population abundance index estimates of 885 to 2,463, with a mean estimate of 1,574 (95% CI: 1,189 – 2,021) beluga in 2014.
• The 2014 abundance index is the second highest in the time series of visual surveys flown since 2001, but a regression analysis using 36 visual estimates from 2001 to 2014 did not show a significant trend.
• Data from a carcass monitoring program indicate year-to-year variation, but no trend in the number of adult beluga carcasses (male and female) reported over the period 1983 to 2014 with a median of 15 whales annually. Since the last population review, the total number of carcasses reported was near this median in 2013 and 2014 with 17 and 11, respectively. The number of reported newborn calves deaths have increased since 2008, and continues to be higher than the 0 to 3 carcasses per year (median = 1) reported between 1983 and 2007. In 2013 and 2014, a total of 5 and 6 newborn calf carcasses, respectively, were found in the SLE.
• The population model represents the most reliable tool for evaluating the trend of the SLE beluga population. The model requires comparable survey estimates of abundance, information on the number, sex and age composition of beluga carcasses recovered, and data on the proportion of calves in the population obtained from photographic surveys. 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 status evaluation for this population.

This Science Advisory Report is from the October 20-23, 2015 Annual Meeting of the National Marine Mammal Peer Review Committee (NMMPRC). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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