Bélugas du Saint-Laurent: Portrait d’une population en voie de disparition en déclin
A sad day for the beluga population of the St. Lawrence, with two dead belugas reported to the Marine Mammal Emergency Response Network of the St. Lawrence Estuary and adjacent gulf. Despite legal protection since 1979 and a comprehensive recovery strategy, the beluga population of the St. Lawrence has been steadily declining for a decade and, since 2008, suffers from alarming mortality patterns.
Our research zodiac, the NARVAL, was about 15 km southeast of Longue-Rive when we discovered the white body floating in the St. Lawrence Seaway, a few kilometers east of the Saguenay-St. Lawrence Marine Park. A short general inspection reveals that the carcass is in excellent condition with no external signs of decomposition, hence, a suitable candidate for a full-scale necropsy at the Faculty of Veterinary Medicine in Saint-Hyacinthe (Québec). It’s an adult female about 4.2 m long with no external injuries, but with a dilated vagina still bleeding – she has probably delivered a short while ago and died during or shortly after giving birth. The calf was nowhere within sight.
We reported our sad finding to the Québec Marine Mammal Emergency Response Network and agreed to tow the carcass to the nearest marina, being the Coast Guard pilot station in Escoumins on the North Shore, resulting in a 4-hour towing operation.
The belugas of the St. Lawrence are the southernmost beluga population, a relic of the last glaciation. The population is estimated to have been around 10’000 animals in pre-whaling times, but got severely depleted in 19th and 20th century coastal whaling operations, with a remnant population of about 500 belugas in 1973. Despite legal protection since 1979, the population recovery was very slow, due in large part to an unusually high cancer incidence of the St. Lawrence beluga population.
A survey by Fisheries and Oceans Canada in 2003 revealed a population estimate of 1100 animals, whereas surveys conducted in 2005 and 2012, yielded estimates of 1000 and 889 animals, respectively. Clear results indicating that after a slight increase, the population has been on a steady decline for a decade. According to Robert Michaud, « It’s a catastrophic trajectory we’re observing, and we don’t know yet exactly what the causes are. The only way this population can reverse its trajectory would be to increase the survival rate and the birth rate, but what we’ve been observing for the last years is totally the opposite. »
2012, the worst year !
In 2012, 16 new-born belugas were found dead. Stephane Lair, veterinary professor at the University of Montreal, has conducted autopsies on the carcasses. Cancer incidence is still unusually high in adult belugas. However, it’s difficult to know the exact cause of the calves’ deaths, but the findings are troubling. « What we think, is that either the calf is too weak to follow the mother, or there is a bonding problem between the calf and the mother. »
Another potential hypothesis is that the females are suffering from perinatal problems which prevent them from taking care appropriately of their new-born calves or which jeopardize their life or that of their baby. Several cases of dystocia (laborious birth due to an anomaly of the mother or the fetus, or a bad position of the fetus) have been diagnosed in female carcasses found in the Saint-Lawrence.
Hopefully, we will be able to implement protection measures to stop this moribund trend and conserve the St. Lawrence belugas for future generations.