As the Gulf of St. Lawrence faces rapid environmental changes driven by rising ocean temperatures, shrinking sea ice, and increasing human activity, the region’s fin, humpback, and minke whales are adjusting their feeding habits to coexist and divide limited food resources.
A long-term study published in the journal Frontiers in Marine Science has revealed that these whale species are now consuming more fish and less krill than they did in the past. Researchers analysed skin samples collected from over 1,100 whales between 1992 and 2019, using stable nitrogen and carbon isotopes to track their dietary shifts.
The findings show that all three whale species have gradually shifted towards fish-based diets, with Arctic krill – a key prey species – playing a smaller role. Fin whales, which previously fed mainly on krill, have increasingly turned to fish such as capelin, herring, and mackerel, while humpback whales have consistently relied on a small number of fish species.
“A recent increase in resource partitioning among fin, humpback, and minke whales in the study area may reflect an increased competition level in response to limited resource availability,” said Charlotte Tessier-Larivière, the study’s lead author from Canada’s Maurice Lamontagne Institute.
As Arctic krill becomes less abundant due to warming waters and changing ocean conditions, the whales appear to be sticking more closely to their own dietary “niches” to reduce competition. However, the researchers found no evidence that one species is displacing another, suggesting the ecosystem remains productive enough to support the co-existence of these highly mobile baleen whales.
“Rapid environmental changes occurring in the Gulf of St. Lawrence seem to have already impacted rorquals (the largest group of baleen whales),” Tessier-Larivière said. “It is crucial to monitor their trophic niche and consider this information for fisheries management and the development of marine protected areas.”
The study provides rare insight into how large marine animals respond to long-term ecosystem changes, rather than short-term fluctuations. It adds to the growing body of evidence showing how the climate crisis is altering marine food webs in subtle yet significant ways.
