Potential impacts of shipping lane rerouting on St. Lawrence belugas (2015)

The St. Lawrence Seaway is a gateway to North America. When they arrive in the Estuary, vessels pass through the heart of whale feeding grounds and the summer habitat of belugas. Concern has been raised over collisions between ships and whales, or between ships and whale-watching boats. Authorities of the Saguenay-St. Lawrence Marine Park and those of the St. Lawrence Estuary Marine Protected Area (MPA) project, through the Working Group on Marine Traffic and Protection of Marine Mammals (G2T3M), have proposed measures to lower the risks of collision, including reducing the speed of ships to 10 knots at the head of the Laurentian Channel in the North Channel while allowing pilots to shift their course toward the South Channel, on the other side of Île Rouge, thereby avoiding the whale concentration zone and the reduced speed zone. Fisheries and Oceans Canada (DFO) has examined the possible impacts of this scenario on the St. Lawrence beluga population.

Study method

To characterize beluga habitat and the proportion of the population and critical habitat exposed to noise under the two scenarios, data on beluga density, maritime traffic volume, sound propagation in the environment, and acoustic signatures of different ships have been collected, mostly between May and October, the period when whales are most present.

Changes in the risks of collisions between ships and belugas, considered to be low due to the low, predictable speeds of freighters as well as the agility and acute hearing of belugas, were not taken into account in this comparative study.

Presently, commercial shipping in the Estuary exposes multiple times daily a significant portion (15-53%) of the beluga population to noise levels likely to trigger adverse effects in a majority of individuals exposed. In this affected portion are a large majority of females accompanied by calves or juveniles.

Rerouting traffic toward the South Channel would bring about an increased proportion of the population and critical habitat exposed to higher sound levels, which is all the more alarming since the sector is frequented by females and their young. Further, to date this sector has had reasonably little exposure to shipping noise; an increase in merchant ship traffic would therefore represent a deterioration of this habitat currently relatively protected from noise. Also to be considered is the fact that the ships most likely to opt for the South Channel in order to avoid the reduced speed zone would probably be container ships, i.e. the largest, fastest and loudest vessels. Reducing speeds in the North Channel would help lower the exposure of belugas and their habitat to the ramifications of noise.

Consequently, maintaining or concentrating merchant navigation in the North Channel as much as possible represents the scenario that would best minimize the impacts on belugas. Reducing the speed or size of ships, changes in their design, or any other measure that would make them quieter would help further mitigate these adverse effects.

Références bibliographiques

DFO. 2013. Impacts of rerouting marine traffic in the St. Lawrence Estuary on beluga (Delphinapterus leucas): Science in support of risk management. DFO Can. Sci. Advis. Sec. Sci. Advis. Rep. 2013/nnn.

Lesage, V., McQuinn, I.H., Carrier, D., Gosselin, J.-F., and Mosnier, A. 2013. Exposure of the beluga (Delphinapterus leucas) to marine traffic under various scenarios of transit route diversion in the St. Lawrence Estuary. DFO Can. Sci. Advis. Sec. Res. Doc. 2013/ 125. iv + 28 p.