Research Document 2017/027
Predicting responses of St. Lawrence beluga to environmental change and anthropogenic threats to orient effective management actions
By Williams, R., Lacy, R.C., Ashe, E., Hall, A., Lehoux, C., Lesage, V., McQuinn, I., and Plourde, S.
Abstract
The St. Lawrence Estuary (“SLE”) population of beluga (Delphinapterus leucas) was depleted by hunting. The population failed to increase in numbers at the rate one would expect after cessation of hunting. We conducted a population viability analysis (“PVA”) to quantify factors that most likely limit recovery of SLE beluga. The main threats considered were: changes in prey abundance; changes in foraging efficiency caused by underwater noise and disturbance; and chemical pollution, namely polychlorinated biphenyls (“PCBs”). Although all three threats have received scientific and management attention, there is greater evidence available to quantify the relationships between prey and demography than between noise or PCBs, and demography. The primary objective was to use best available science to build a framework to predict how the population might respond to changes in environmental conditions and varying levels of the three main anthropogenic threats. This tool will provide information on the relative importance of each threat (across a range of input values), and identify knowledge gaps needed to be filled in order to improve mitigation and monitoring of effects, and research activities. As the quantity and quality of data on the three threats and demography increase, the tool will allow end-users to explore the likely fate of the population under alternative management actions to mitigate threats. Having built a framework that simulates how big a given population-level effect might be at varying levels of anthropogenic threats, a discussion among scientists and managers is needed next to gauge where we think the population might be along the spectrum for each threat. This may include identifying plausible ranges for threats that might have existed in the past and may have influenced demographic parameters. This will inform threat scenarios that might exist in the future, either under climate change predictions or due to management actions.
Across the range of stressors we considered, data were only available to link threats to changes in calf mortality. Additional research is needed to assess whether stressors could influence pregnancy or adult mortality. Uncertainty in current demographic rates, especially adult mortality, and their functional relationships to environmental conditions and threats together contributed twice as much to our uncertainty in the future trajectory of the population as did the ranges of possible management actions that were considered. The effects of prey availability contributed most to changes in calf mortality, followed by noise and PCBs. The report outlines important caveats with all three threats, which may influence the relative importance of each. Although we considered management scenarios that reduced threats singly and in combination, no management scenario resulted in the population reaching a previously identified recovery target of 7,070 individuals by 2100.
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