Research Document - 2013/129

Ecosystem perspective on changes and anomalies in the Gulf of St. Lawrence: a context in support of the management of the St. Lawrence beluga whale population

By Stéphane Plourde, Peter S. Galbraith, Véronique Lesage, François Grégoire, Hugo Bourdages, Jean-François Gosselin, Ian McQuinn, Michael Scarratt

Abstract

The St. Lawrence beluga whale (Delphinapterus leucas) population is at the southernmost limit of the species. In spite of > 30 years protection, there is little or no indication that the population is recovering. The main objective of this study is to characterize long-term changes in the environmental conditions likely to have an impact on beluga population habitat at the scale of the Gulf of St. Lawrence. We used a set of 94 physical and biological parameters to describe different components of the ecosystem. Principal Components Analyses (PCA) were performed to extract the dominant environmental patterns. Shifts in environmental regimes in the time series were identified using sequential t-test analysis of regime shifts (STARS). Our analyses revealed periods during which beluga whale ecosystem parameters changed (late 1990s, mid and late 2000s), such as demersal and pelagic fishes availability and composition, ocean temperature and winter sea ice dynamics. A decrease in the percentage of young beluga in the population and an increase in calf mortality occurred during a period initiated in the late 1990s during which large demersal fish and spring herring biomass was at its lowest and ice coverage was below normal. More recently, years of high calf mortality corresponded to an abrupt decrease in ice cover and duration. The analysis of these environmental parameters over a longer period (1971-2012) revealed that environmental conditions switched from a positive regime, i.e. apparently promoting positive anomalies in beluga population indices, to a predominantly negative regime around 1998, a situation that has worsened since 2009. Our results provide a general ecological context for beluga whale management and suggest that the long-term degradation of suitable prey availability and its winter habitats on the scale of the GSL may explain the population’s lack of recovery.

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