Canadian marine mammal researchers are sounding the alarm about beluga deaths in the St. Lawrence Estuary, after a majority of the carcasses recovered last year were once again found to belong to pregnant females, new mothers and newborn calves.
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The figures, provided by Fisheries and Oceans Canada to Radio-Canada, are part of a "worrisome" trend, said federal research scientist Véronique Lesage.
Of the 14 carcasses recovered in 2015, six were newborn calves and three were pregnant.
In 2014, 11 beluga carcasses were recovered, and six of them were babies. In 2013, 17 dead belugas were found, and four of them were babies.
Necropsy findings are cause for concern
Post-mortem investigations conducted at the University of Montreal's faculty of veterinary medicine in St-Hyacinthe have shown that the deceased adult females were either just about to give birth or had just given birth.
One female beluga found on a riverbank in 2015 had a ruptured uterus.
Carcasses of newborn belugas, meanwhile, showed no signs of injury, infection or tumours, suggesting to researchers that they died of starvation or dehydration because they had been separated from their mothers.
Since 1983, all belugas found dead in Quebec have undergone necropsies (post-mortem investigations) at the St-Hyacinthe veterinary centre.
For the first 25 years of that program, in any given year, there were never more than three beluga calves found dead and sent for autopsies.
However, in seven of the past eight years, three or more calves are known to have died annually.
Stéphane Lair, a veterinary professor in St-Hyacinthe, called the situation an "epidemic."
These deaths are "very unusual for a wild animal," he said.
Population in jeopardy
Robert Michaud, the scientific director of Quebec's Marine Mammals Research and Education Group, said the number of belugas in the St. Lawrence has been in decline since the early 2000s, with a drop of 1.0 to 1.5 per cent per year.
He said the decline is approaching a crisis level.
"The potential of the population to recover is disappearing with these deaths," Michaud said.
There are currently an estimated 900 belugas in the St. Lawrence Estuary, according to Fisheries and Oceans Canada.
Fifteen years ago, there were at least 1,000 belugas, and a century ago there were 10,000.
Following a ban on beluga hunting in the 1970s, their numbers should have increased, but the opposite happened.
Researchers have come up with four main hypotheses to explain the decline of the beluga whale, including:
- Contaminants in the water such as polybrominated diphenyl ethers (PDBEs), which were banned more than a decade ago but remain present in the environment.
- The decline in the number of herring in the St. Lawrence Estuary, a valuable source of food for beluga mothers and their young.
- The absence of ice cover due to rising water temperatures. The ice serves as protection against wind, waves and storms.
- The rise in marine traffic, which can be disruptive, particularly to female belugas and their calves who use sound to communicate.