Research Document - 2016/090

Spatial-temporal exposure of blue whale habitats to shipping noise in St. Lawrence system

By Florian Aulanier, Yvan Simard, Nathalie Roy, Cédric Gervaise, and Marion Bandet

Abstract

Blue whales frequenting the Estuary and Gulf of St. Lawrence are exposed to anthropogenic underwater noise from the main shipping route of Eastern Canada that connects the Great Lakes to the Atlantic, the St. Lawrence Seaway. This shipping underwater noise is concentrated in the low-frequency band used by baleen whales for their regular acoustic communications. The effects of this anthropogenic noise on the quality of this habitat of Northwest Atlantic blue whales, a population considered endangered under the Canadian Species at Risk Act, is a general concern. The first steps for assessing these effects include the establishment of the actual characteristics of this noise over time and space in the areas exploited by the whales throughout the annual cycle. This problem is addressed here by ground-truthed numerical simulations using information from in situ acoustic measurements, actual traffic, environmental conditions, and sound propagation modeling.

The cumulative distribution functions (cdf) of shipping noise radiated in blue whale call frequency band in the ~290 000 km² basin during typical summer and winter months were computed for 10 depth layers with a 1-km² resolution. This information was then used to map the risk of exceeding given noise thresholds or the likelihood of remaining under given noise levels, in an effort to identify at-risk and quiet areas. The role of the seaways and modulations by the three-dimensional (3D) basin shape are illustrated. The masking blue whale A- and D-calls by shipping noise was estimated with time budgets at representative locations in the Estuary and Gulf of St. Lawrence. Both calls are masked in the vicinity of shipping lanes, which fragment the communication space in several pieces. Compared to the prevailing conditions before the motorized shipping era, the masking by present shipping noise has much more affected the D-calls than the A-calls.

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