abstract

The St. Lawrence Estuary (SLE) beluga (Delphinapterus leucas) population is currently estimated at 1100 animals, reduced to less than 15% of estimated pristine population size in the late XIXth Century. The decline in population is due primarily to hunting which was stopped in 1979. The population was designated as endangered in 1983 and re-evaluated as threatened in 2004. Legislative, regulatory and management measures were instituted to protect this population. Despite protection and an absence of predators and hunting, recent aerial surveys indicate few signs of recovery. Since 1982 mortalities of SLE beluga have been documented and causes of mortality investigated through dissection of beach-cast carcasses by the University of Montreal, St-Hyacinthe in partnership with Fisheries and Oceans Canada and Parks Canada. From 1983 to 2007 over 365 mortalities have been documented with a mean of 15 (9-21) per year which reflects effort rather than true mortality. The age of beluga is determined by counting the number of growth layer groups (GLG) in longitudinal sections of teeth, with one GLG deposited per year. The mean age of stranded SLE beluga carcasses is 34 years with a peak at 41 to 50 years. The oldest SLE beluga is over 80 years old. Documented causes of death (all age and sex classes) include infectious and parasitic diseases (38%), terminal neoplasia (15%), perinatal/dystocia (7%), trauma (5%) and other (7%). Almost 30% die of unknown causes. In stranded calves (one year old or less), 58% die perinatally. In stranded juveniles (females >1 to 10 years old and males >1 to 14 years old), 81% die of infectious and parasitic diseases, 56% due to verminous pneumonia. In stranded adults (>10 to 14 years old) 32% die of infectious diseases and 18% of terminal neoplasia. The mean age of beluga dead of terminal neoplasia is 33 years (range of 22 to 59). Beluga whales, like many marine mammals worldwide, have various chemical contaminants in their tissues but a cause and effect link between contaminants, neoplasia or other diseases has not been demonstrated. A number of hypotheses have been proposed to explain the failure of this population to recover. The SLE beluga is unique in that disease, including chronic and degenerative diseases linked to age, appears to be playing a large role in this population.