Gulf of St. Lawrence warming is changing whale diets

A long-term Canadian study finds fin, minke and humpback whales in the Gulf of St. Lawrence show increased signals of eating forage fish after a decline in Arctic krill; researchers analyzed tissue isotopes collected over 28 summers.

New Canadian research reports that baleen whales in the Gulf of St. Lawrence are shifting their diets as the water warms. Researchers analyzed tissue samples collected during summer months across 28 years. The team used carbon and nitrogen isotope analysis to track what the whales had been eating. Scientists link part of this shift to a decline in Arctic krill and to greater use of forage fish such as capelin, mackerel and herring. Key findings: - Fin, minke and humpback whales showed increased isotope signatures consistent with eating more forage fish in recent years. - The study relied on carbon and nitrogen isotope analysis of whale tissues and of their prey collected during summer over 28 years. - Researchers noted a decline in Arctic krill, which was an important prey for fin whales in earlier decades. - Despite sharing the same pool of prey, the study found signs of resource partitioning, with reduced overlap suggesting whales may feed at different times or places. - The area studied was not inside a marine protected area; there are existing protected zones deeper in the St. Lawrence and plans for expansion have been discussed. Summary: The findings suggest some whale species are adjusting their diets in response to changing prey availability, but researchers say the full extent of their adaptive capacity is unknown. Advocates and scientists have highlighted implications for prey stocks and marine protection, and specific policy or management outcomes are undetermined at this time.