Some Belugas More Affected than Others by Underwater Noise

How do researchers determine belugas’ exposure level to noise pollution caused by maritime traffic? There are several methods. Conventional, habitat-oriented approaches consist of overlaying underwater noise maps with animal distribution maps. For simplicity, such approaches will either consider that all whales can go anywhere within their habitat (“spatially mixed” in scientific jargon), or be based on the premise that whales are stationary in this habitat (“spatially static”). However, these two hypotheses are not realistic when we consider how whales really behave, and the choice of hypothesis has a significant impact on the results obtained.

Using this new model to simulate ship and beluga movements, the researchers were able to determine that, over their lifetimes, some belugas were much more exposed to noise than others. However, this individual cumulative exposure goes undetected with conventional modeling methods, which only allow the impact to be assessed at the population and habitat levels. Why is this essential for beluga conservation? By evaluating acoustic impact – current or future – at the population level, researchers run the risk of underestimating noise pollution levels affecting the most exposed individuals. Acoustic impact studies would then be biased and the shipping and boating recommendations issued would be poorly suited.

Take the Saguenay Fjord, for example, an important summer area for the St. Lawrence beluga. Individuals are present here almost every day between June and October. In their study, Clément Chion and his team found that belugas that regularly visit the area seem to have less cumulative exposure to noise pollution. This sort of refuge is important for the species, as anthropogenic noise in the Estuary is particularly high.

Unfortunately, projections show that global maritime traffic is expected to surge between now and 2030. Should maritime traffic in the Saguenay River increase, the effect would be magnified. Indeed, the narrowness of the Fjord forces belugas into close contact with passing ships, resulting in very high noise exposure. Any increase in shipping traffic in the Saguenay would therefore quickly lead to higher levels of cumulative noise exposure for belugas frequenting the Fjord, depriving them of a quiet sector within their habitat.

Who exactly uses the Fjord? More than half of all St. Lawrence belugas, and two-thirds of all females! This is the conclusion of the first phase of research by Clément Chion and his team, which was able to show through modelling and behavioural studies that belugas’ use of this area had been underestimated. Females, especially mothers accompanied by their calves, are therefore the most vulnerable individuals as maritime traffic continues to swell. The increase in noise pollution is likely disproportionate for this category of individuals. This risk is all the more serious considering that sound communication is an essential element in the mother-calf relationship.

This finding led researchers in September 2020 to recommend a moratorium on any project that risks increasing maritime traffic in the Saguenay. Recently published findings once again underscore the importance of taking into account the complex behaviours of belugas – both in terms of their social interactions and their movements – when implementing protective measures.