Anxious new year for belugas

2021 will be no exception. Once again this year, the observed mortality of beluga whales in the St. Lawrence River worries researchers and specialists.

In 2021, 19 belugas carcasses were recorded and examined along the St. Lawrence River as part of a carcass monitoring program run by the Quebec Network for Marine Mammal Emergencies (RQUMM). “Unfortunately, this year we still have a high neonatal mortality rate. This is a trend that has been observed over the past decade and is continuing,” worries Robert Michaud, Scientific Director of the Marine Mammal Research and Education Group and coordinator of RQUMM.

Between March and December 2021, 19 carcasses of beluga whales were found on the banks of the St. Lawrence River, including one on Prince Edward Island, which is outside the normal range. For comparison: in 2020 there were 14, in 2019 – 17, in 2018 – 12, in 2017 – 22, in 2016 – 14.

“In 2021, the number of carcasses washed ashore exceeds the 39-year average of 14 carcasses,” said Stéphane Lair, professor in the Department of Veterinary Medicine at the University of Montreal.

Of the 19 carcasses, 11 washed ashore at Ba-Saint-Laurent, four more on the North Bank, two at Gaspesie and one at Charlevoix. Eight of them managed to be transported.

It is important to keep in mind that this is not the total mortality in the population, but the number of individuals found dead that could be sampled or autopsied. In particular, to avoid duplication, carcasses reported to be drifting, not detected, and not sampled are not counted. But carcass samples provide a wealth of information to better understand the dangers that threaten the fragile St. Lawrence belugas population.

Of the people stranded in 2021, ten were adults. If this number is equal to the average value over the last 39 years of collection, this does not apply to calves. “The number of one-year-old calves (6) washed ashore this year is again above the average (1) for the first 25 years of this program (1983 to 2007). However, this is in line with the average (6.3) and average (6) between 2008 and 2020,” says veterinarian Stefan Lair. It is clear that excess calf mortality is a phenomenon that has existed for ten years.

To this must be added another problem: the problem of dystocia, that is, death coinciding with the moment of birth. In a report analyzing the mortality of beluga whales between 1983 and 2012, Stefan Lair’s team concluded that since 2008, difficult births have become the most important cause of death in adult female beluga whales in the St. Lawrence River. This trend continued in subsequent years. And in 2021, two of the females found had cases of dystocia.

REASONS UNKNOWN YET

“There are several hypotheses that explain this excess mortality,” says Robert Michaud. It is possible, for example, that the physical condition of female beluga whales does not allow them to have the energy resources for childbirth, and in this case, excess neonatal mortality will be associated with a reduction in available food resources. We are also thinking about the neurotoxic effects of some bromine-based chemical contaminants, which can affect the health of both the mother and the newborn.

In a scientific review of the St. Lawrence beluga, Véronique Lesage, researcher at Fisheries and Oceans Canada, listed “competing, but not exclusive, hypotheses to explain high calf mortality and demographic changes in the population”: reproductive problems or impairments due to the toxic effects of some chemical compounds on endocrine and immune functions; disruption of essential activities (eg, childbirth and foraging); chronic vascular effects or isolated or recurring disorders; changes in ecosystem structure associated with fisheries or climate, leading to a decrease in habitat quality; habitat quality and prey quality; and recurring stochastic events such as harmful algal blooms.” Thus, scientists still have work to do to determine the dangers that belugas are exposed to.

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