The challenges of a small population exposed to multiple anthropogenic stressors and a changing climate: the St. Lawrence Estuary beluga

There are competing, not exclusive, hypotheses for the observed high calf mortality and change in the demography of the St. Lawrence Estuary beluga population. These include health problems or impaired reproductive functions from the toxic effects of specific chemical compounds on endocrine and immune functions; perturbation of critical activities from chronic vessel exposure or isolated or repeated disturbance; fishery- or climate-related changes in ecosystem structure leading to a decrease in habitat quality and prey availability or quality; and recurring stochastic events such as harmful algal blooms

VĂ©ronique Lesage

2021

Scholarcy highlights

  • The incorporation of this information in an age-structured population model, along with abundance estimates from the photographic survey time series and numbers of dead calves and non-calves reported through the carcass monitoring programme, indicated that several aspects of St. Lawrence Estuary beluga demography had changed over time
  • There are competing, not exclusive, hypotheses for the observed high calf mortality and change in the demography of the St. Lawrence Estuary beluga population. These include health problems or impaired reproductive functions from the toxic effects of specific chemical compounds on endocrine and immune functions; perturbation of critical activities from chronic vessel exposure or isolated or repeated disturbance; fishery- or climate-related changes in ecosystem structure leading to a decrease in habitat quality and prey availability or quality; and recurring stochastic events such as harmful algal blooms
  • The very slow population growth rate observed during the 1980s and 1990s despite the total halt on hunting suggests that population growth was already constrained by anthropogenic stressors or sub-optimal environmental conditions associated with local climate, or both
  • While a harmful algal bloom event was likely responsible for the unusually high calf mortality in 2008, the timing of the change in population dynamics and of increased calf mortality suggests that warming environmental conditions and a decrease in sea-ice extent and duration, with their cascading effects on ecosystem structure, may be key drivers of the current population decrease and the persistently high calf mortality
  • The apparent deterioration of SLE beluga body condition over the past 20 years supports a hypothesis in which climate or fishery-driven impacts on energy balance likely play an important role, by reducing prey availability, quality or both
  • Poorer body condition can arise solely from an increase in energy output caused by anthropogenic stressors, for example, repeated avoidance response

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