Research Document - 2007/026

Lack of Recovery in St. Lawrence Estuary beluga

By Hammill, M.O., L.N. Measures, J.-F. Gosselin, and V. Lesage

Abstract

Estimates of pristine population size and changes in abundance of St. Lawrence Estuary beluga were examined over the period 1866-2006. Overhunting led to a decline in abundance from pristine estimates of 7,800 (SE=600) in 1866, to approximately 1,000 animals in 1985. In spite of almost 30 years of protection from hunting, the St. Lawrence Estuary beluga shows no signs of recovery with a current population of approximately 1,100 (SE=300, 95% CI=500-1,800, rounded to the nearest 100) animals. A carcass monitoring and necropsy program detects on average 15 carcasses per year, which likely represents a fraction of the total number of deaths in this population. The age structure of adult animal carcasses suggests that adult mortality rates (6.5%/yr) are similar to what would be expected in a hunted Arctic beluga population (7.0%/yr) (Burns and Seaman 1985). Estimates of reproductive rates are uncertain, and juvenile animals are under-represented in the stranding record. Among all animals regardless of age class where cause of death could be determined, parasitic and bacterial infections accounted for 38% of mortality, followed by cancer (15%), problems during birth (7%), and trauma (5%), while various other factors accounted for 7%. A paucity of diet information limits attempts to model trophic interactions and habitat requirements. Emigration does not appear to be an important factor, but the loss of only 1-2 animals per year has longer term cumulative impacts that are not beneficial to a small population.

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