Science Advisory Report 2014/004

Impacts of Rerouting Marine Traffic in the St. Lawrence Estuary on Beluga (Delphinapterus Leucas): Science in Support of Risk Management

Summary

• The St. Lawrence Estuary (SLE) beluga population is listed as threatened under the Canadian Species at Risk Act (SARA), which protects species at risk from being killed or harmed (section 32; Appendix I) and protects any part of their Critical Habitat from destruction (section 58; Appendix I).
• Marine traffic may affect SLE beluga mainly through generated noise as risks of collision with large, slow moving vessels are considered low for beluga given their high maneuverability and acute hearing. Based on a review of studies, negative behavioural responses to continuous noise sources are expected at a threshold of 120 dB re 1 μPa (rms) for cetaceans such as the beluga, with best hearing sensitivity in the mid-frequencies.
• Data on marine traffic volume, ship acoustic characteristics, local sound propagation conditions and summer SLE beluga densities from 35 aerial surveys were used to determine areas of beluga concentration, the proportion of the population, and of Critical Habitat exposed to marine traffic under (a) the current traffic conditions and route (mainly through the North Channel (NC)) and (b) an alternate Hybrid scenario, which involves a speed limit of 10 knots and a probable increase in deviation of route to the South Channel (SC). The extent of negative effects on the beluga population associated with these two scenarios was evaluated.
• From our simulations, each commercial ship transiting by the current North Channel (NC) shipping route exposes between 15-48% of the beluga population to noise levels likely to cause behavioural responses in a majority of individuals, depending on its source level and direction of transit. The vast majority (72-80%) of the beluga exposed are females with calves or juveniles (FCJ).
• Vessels currently diverting part of their path toward the SC increase beluga exposure to noise of this magnitude by 7-11% per transit compared to those staying in the NC, resulting in 16-53% of the population being exposed to shipping depending on the vessel source level, direction of transit and specific route in the SC. Vessels using the SC during part of their transit reduce their overall encroachment on the beluga areas of concentration by 2-3% depending on SL, but increase exposure of beluga designated Critical Habitat by 3%.
• Under the proposed Hybrid scenario, there would be a 10-12% lesser exposure of the beluga population, and 7-11% lesser exposure of their Critical Habitat, simply by the effect of reducing speed to 10 knots for those noisy ships which remain in the NC.
• The ships most likely to choose the alternate route, therefore to spend the least time in the speed-reduced zone, are the largest, fastest and noisiest (i.e., with cruising speeds >14 kt). Considering only these vessels (mainly container ships), noise exposure under the alternate SC Hybrid scenario increases beluga exposure by 21%, and exposure of their Critical Habitat by 17% relative to the NC route with reduced speed, i.e., without deviation to the SC. As with other deviations to the SC, this scenario reduces exposure of herds of adult beluga and their habitat, but increases exposure of FCJ and of the population Critical Habitat.
• Commercial shipping is currently concentrated in the North Channel of the SLE, with 90-94% of the vessels following the NC. As a result of this traffic and commercial whale-watching, this zone is highly ensonified. Islands in the middle of the SLE create a sound shadow for FCJ habitat located along the south shore. Diverting some of the shipping traffic to the South Channel would considerably reduce the amount of noise-shelter areas for FCJ.
• The above findings are for a single ship transit and need to be expanded to the volume of traffic. Commercial transits of all vessel types occur on average 18 times daily, resulting in each beluga being exposed several times a day to noise likely to affect their behaviour. Considering only those vessels likely to use the SC, there is a potential for an almost tripling of the frequency of exposure of FCJ in this lightly exposed habitat (2 additional exposures / day).
• The proportion of exposed beluga that is likely to be negatively affected by noise to the point where reproduction, health or survival is compromised is unknown. However, SLE beluga are not immune to disturbance and displacement, as they have abandoned Tadoussac Bay when a marina was established, and were documented to modify their vocal behaviour in response to masking by ferry noise.
• The SLE population size had shown little change for several decades, but seems to have been recently declining, suggesting that harmful natural or anthropogenic factors are at play in their lack of recovery. The relative role of natural and anthropogenic pressures, including environmental change, contamination, toxic algal blooms and marine traffic on individual health, reproduction and survival and thus, on the potential for population growth cannot be determined.
• The proposed Hybrid scenario with route diversion to the SC is likely to have negative, at best neutral, effects on SLE beluga recovery as it increases the vessel-noise footprint in FCJ habitats, and the beluga Critical Habitat, and contributes to the acoustic degradation of some areas of concentration previously only lightly exposed to shipping noise.
• Maintaining or concentrating as much as possible commercial traffic in the NC constitutes the scenario which minimizes impacts on the SLE beluga.

This Science Advisory Report is from the October 7-11 2013 Annual Meeting of the National Marine Mammal Peer Review Committee (NMMPRC). Additional publications from this process will be posted the on Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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