Record High Number of Beluga Calf Mortalities Reported in the St. Lawrence Estuary
Since the beginning of the calving season, a total of 14 dead beluga whale calves have been recovered in the St. Lawrence Estuary. This represents by far the largest number of calves reported in a given year since the beginning of the monitoring program 30 years ago. From 1983 and 2007 the number of dead calves recovered each year ranged from 0 to 3. Higher than average calf mortalities were observed in 2008 (8 calves) and 2010 (9 calves). Three of the 14 calves that were found dead this year were submitted for necropsy. So far, post-mortem examination has failed to detect any pathological process that could account for these mortalities. It is believed that most, if not all, calf mortalities were due to calf-mother separation leading to starvation and dehydration of the lost calf. The cause of this possible increase in the rate of calf-mother separation is at this time unclear. Potential explanations that are currently being investigated include: difficulty in the birthing process resulting in a weak mother and/or calf, increased disturbances in calving ground by recreational activities, and sublethal effect of a biotoxin on the dam resulting in mismothering. The high number of dead calves observed in 2008 was believed to be a due to an unusual occurance of red tide that released saxitoxine. The observation of mortalities of marine birds, fish and invertebrates over the month of August suggests that toxic harmful algal blooms have occurred in the St. Lawrence Estuary this summer. Tests are currently underway to confirm this suspicion. Another potential risk factor to explain an emergence of prolonged or difficult birthing processes, and therefore increased calf mortalities, is the exposure of the dams to endocrine disrupting xenobiotics such as polybrominated diphenyl ethers. This unprecedented occurrence is closely monitored by the Reseau d’urgence des mammifères marins in collaboration with the CCWHC – Quebec Regional Center as well as governmental and non-governmental conservation agencies.