Mortality 2021: An Ominous Year for Belugas

It is important to bear in mind that these figures do not reflect the total mortality in the population, but rather the number of individuals found dead that could be sampled or necropsied. Carcasses reported adrift, not found and not sampled are not included in the tally, namely to avoiding double-counting. Sampled carcasses contain a wealth of information that can help better understand the dangers that threaten the fragile population of belugas in the St. Lawrence.

Another problem is dystocia, i.e. a death that coincides with calving. In a report on beluga mortalities occurring between 1983 and 2012, Mr. Lair’s team concluded that, since 2008, calving difficulties had become the most important cause of mortality for adult female belugas in the St. Lawrence. This trend continued in the years that followed. And in 2021, two of the females discovered were found to have suffered from dystocia.

Causes still unknown

“There are a number of hypotheses to explain this excess mortality,” specifies Robert Michaud. “For example, it is possible that female belugas are not physically fit enough or that they lack the necessary energy reserves to give birth, in which case excess neonatal mortality might be attributable to a decline in available food resources. Also at play may be the neuro-toxic effects of certain bromine-based chemical contaminants, which can impact the health of both mother and newborn.”

In a scientific review devoted to the St. Lawrence beluga, Fisheries and Oceans Canada researcher Véronique Lesage listed “competing, although not exclusive, hypotheses for the observed high calf mortality and change in the demography of the [St. Lawrence Estuary] beluga population, [including] health problems or impaired reproductive functions from the toxic effects of specific chemical compounds on endocrine and immune functions; perturbation of critical activities (e.g., parturition and foraging) 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.” Scientists therefore still have their work cut out for them to identify the dangers to which belugas are exposed.