Climate Change Compromising Beluga Recovery

It is established that the belugas of the St. Lawrence face a number of so-called sublethal threats. In other words, these threats are a not a direct cause of beluga mortality such as entanglement or ship strikes, but they do exert pressure that, over the long term, puts strain on the animals’ health and their ability to survive. Rob Williams and his team therefore created a viability model, i.e. a mathematical projection to assess the long-term effects of these stressors on population growth. Three main ‘suspects’ were taken into account.

Another notable stressor is the presence of anthropogenic underwater noise. This is caused by the heavy maritime traffic in the region, including commercial ships, ferries, pleasure craft and whale-watching cruises, all of which produce ambient noise in beluga habitat. The species’ essentially sound-based communication is therefore disrupted. Calves are especially vulnerable to this threat.

The availability of the beluga’s main prey, including herring and groundfish, was also taken into account in the researchers’ viability model. These prey are suspected to be highly variable, or even decreasing, over the past several years, which is likely having an impact on the ability of the population – particularly calves – to survive.

Two major conclusions emerge from the projections made by Rob Williams and his colleagues. First, the researchers found that minimizing just one – or even two – of the three main stressors would not be enough for the population to rebound. Indeed, all three factors would need to be mitigated to allow for a recovery. However, even in the best current scenarios, it is estimated that the St. Lawrence beluga population would grow at a mere 0.3% per year.

Why such a low figure? According to the researchers, this might be explained not only by the belugas’ reduced reproductive capacities in recent decades, but also by an important new finding. A fourth element was integrated into the complex equation of their recovery: climate change.

Indeed, though not directly responsible for the precarious situation of belugas, climate change reduces the resilience of these cetaceans by changing and affecting vital elements of their environment while amplifying some of the threats that are already present.

For example, seasonal ice is essential for belugas, helping to buffer against strong offshore waves in winter, thus reducing the effort the animals have to make to brave the currents. However, winter ice cover of the St. Lawrence has been declining for several years, and was even absent in 2021[DA1]  (article in French). It is therefore hypothesized that belugas must expend greater amounts of energy in winter than they did before, which likely undermines their fitness.

Moreover, less ice means smoother sailing for ships. If the trend continues, a potential uptick in winter maritime transport in the St. Lawrence and ensuing noise pollution would therefore be possible in the years to come.

One can also question the impact the decline in winter ice cover is having on the beluga’s prey. Seasonal ice is essential to the life cycle of a number of aquatic species, so it is possible that its reduction will have an effect on the beluga’s food chain.