Abstract

From 1983 to 2012, complete post-mortem examinations were conducted on 222 beluga whales found dead in the St. Lawrence Estuary, Québec, Canada. Signs of recent or impending parturitions were observed in 19 of the 91 sexually mature females examined: 11 from 1983 to 2009 (15% of the examined mature females, yearly average of 0.4) and 8 from 2010 to 2012 (50%, yearly average of 2.7). Dystocia or post-partum complications were identified as the presumed cause of death in 17 of these females: 9 (12%, yearly average of 0.3) from 1983 to 2009, and all of the 8 females examined from 2010 to 2012. Concurrently, numbers of newborn calves found dead have increased from a yearly average of 1.2 (1983 to 2009) to 9.3 since 2010. So far, post-mortem investigations have failed to identify a cause for these parturition-associated mortalities. Although the relatively high number of dead calves observed in recent years could be indicative of an increase in the reproductive rate, field observations on live belugas and the concurrent increase in mortalities of females during the peri-partum period rather suggest an increase in the occurrence of reproductive problems in this population of endangered whales. Hypotheses proposed to explain this include contamination with endocrine disrupting xenobiotics such as polybrominated diphenyl ethers, exposure to saxitoxins produced by harmful algal blooms, nutritional stress and disturbance by recreational activities. Ongoing monitoring of calf production and mortality should determine whether these changes are transient or a new significant issue threat to recovery of this population.

* Presenting author