Research Document - 2013/125

Exposure of the beluga (Delphinapterus leucas) to marine traffic under various scenarios of transit route diversion in the St. Lawrence Estuary

By V. Lesage, I.H. McQuinn, D. Carrier, J.-F. Gosselin and A. Mosnier

Abstract

The St. Lawrence Estuary (SLE) marine shipping lane currently overlaps with the main aggregation area for large baleen whales, male beluga and whale-watching activity, raising concerns for potential whale/ship or whale-watch vessel/ship collisions. Motivated by the desire to reduce collision risks, authorities from the Saguenay-St. Lawrence Marine Park and the future Marine Protected Area through the Groupe de Travail sur le Trafic Maritime et la Protection des Mammifères Marins (G2T3M) have proposed to the marine transport industry to reduce vessel speed to 10 kt within a particularly sensitive area at the head of the Laurentian Channel in the North Channel (NC), while leaving pilots the option of diverting their route to the South Channel (SC), thereby avoiding most of the speed-reduction zone and areas of whale aggregation. The present study indicates that commercial traffic transiting through the SLE exposes many times daily a substantial proportion (15-53%) of the SLE beluga population, of which the vast majority (72-81%) are females with calves or juveniles, to noise levels likely to induce negative behavioural responses in a majority of the exposed individuals. Diverting shipping to the South Channel not only increases the proportion of the population and its habitat (including designated Critical Habitat) exposed to noise levels in excess of the threshold for negative behavioural responses, but also contributes to the acoustic degradation of beluga habitat south of Île Rouge, previously relatively lightly exposed to shipping noise. We therefore conclude that maintaining or concentrating commercial traffic as much as possible in the NC constitutes the scenario which minimizes impacts on beluga and their habitat. A reduction in vessel speed or size, changes in vessel designs, or any other measure that might make vessels quieter, would contribute to reducing potential negative effects on SLE beluga.

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