The unexplained deaths of St. Lawrence belugas

The summer of 2012 was marked by a record number of deaths of baby beluga whales in the St. Lawrence estuary. Was this a singular event, or the start of a disturbing trend?

Researchers from Université de Montréal’s faculty of veterinary medicine have monitored populations of the little white whale for the past 30 years. The number of beluga calves stranded along the shores of the St. Lawrence typically does not exceed three per summer. In 2008, however, there were eight. At the time, this phenomenon was explained by a “red tide,” a bloom of the toxic algae Alexandrium tamarense. In 2010, there were nine strandings, with a spike to 16 in 2012.

“Autopsies did not reveal any illnesses or injuries on these calves, which leads us to believe they died as a result of premature separation from their mothers,” explained Stéphane Lair, a wildlife health specialist and professor in the faculty of veterinary medicine at Université de Montréal. “We must therefore determine why this separation is occurring more often.”

Toxic algae once again top the list of suspects. “Alexandrium tamarense is a neurotoxin, which partially paralyzes afflicted animals,” Dr. Lair noted. “It’s possible that a greater accumulation of this neurotoxin in female belugas reduces their ability to care for their calves.” Analysis of the carcasses was expected to conclude by December, and the results should help clarify this unfortunate mystery.

The calves’ death may possibly be linked to a second worrisome phenomenon, the death of female belugas during calving, which occurred in eight of fifteen females found dead between 2010 and 2012. While the cause has not yet been identified, the researcher is following several leads. “Increasingly, new contaminants are being found in beluga habitats, including polybrominated flame retardants,” said Dr. Lair. “These products are known to disrupt thyroid gland activity, which is crucial for mammals during the birthing process.”

A fragile population

The St. Lawrence beluga population remains extremely fragile. Their numbers are difficult to pin down, but the most recent survey, from 2003, estimates the population at roughly 1,100.
According to the St. Lawrence Beluga Recovery Plan of Fisheries and Oceans Canada, the department was expected to publish surveys every three years, but this idea seems to have fallen by the wayside. No survey was undertaken in 2006 nor in 2012, and although a survey was indeed performed in 2009, its results were never published.

Between 8,000 and 10,000 belugas populated the St. Lawrence estuary before being decimated by aggressive hunting, which has since been banned. Estimates show that to ensure the survival of the herd, a minimum of 6,000 whales is required. “An insufficient population will not allow the herd to survive should an unfortunate event occur,” said Dr. Lair.