Whales Are Sharing Food — Not Because There’s More, But Because There’s Less

Whales returning to the Gulf of St. Lawrence are increasingly sharing the same food, a trend that reflects how warming waters and shifting prey are reshaping one of the North Atlantic’s most important feeding grounds.

The Gulf of St. Lawrence is an important seasonal stopover for multiple species of whales who come there every summer to replenish their energy reserves. As waters warm, ice cover decreases, and prey availability becomes less predictable, whales face the problem of coexistence while food is harder to find. A new long-term study, published in Frontiers in Marine sciencessuggests that fin whales, humpback whales, and minke whales are adapting not by competing with each other, but by reshaping how they share resources.

“Highly mobile species like baleen whales can use several strategies to reduce competition, for example by changing their feeding time or area, or by selecting different prey within a feeding area,” said first author Charlotte Tessier-Larivière, in a press release.

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Track whales sharing food in a warming ocean

The findings are based on a 28-year study published in Frontiers of marine science which has tracked the changing diet of whales in the Gulf of St. Lawrence since the early 1990s. Researchers analyzed the carbon and nitrogen isotope signatures of more than 1,100 skin samples collected from fin, humpback, and minke whales between 1992 and 2019, using these chemical markers to reconstruct long-term dietary habits.

Over three periods of warming waters and ecosystem change, all three species showed a consistent trend away from krill and toward fish like capelin, herring and mackerel. But instead of converging on the same diet, their main dietary niches have become more distinct in recent years.

Share food without crowding out competitors

In the early 2000s, there was significant overlap in whale feeding niches. Minke whales, in particular, shared about 65% of their main dietary niche with fin whales and humpback whales combined. Humpback whales overlapped with mink by about 56 percent, while fin whales overlapped with mink by about 42 percent.

In the 2010s, niche overlap decreased across the board. Minke whales still shared their food with other species, but the overlap had fallen to about 47 percent. Humpback whales showed a much more marked change, with the overlap with minks dropping to around 9 percent. Fin whales also reduced overlap with minks, from 42 percent to about 29 percent, while overlap between fin whales and humpback whales remained near zero.

Rather than converging on identical diets, the whales appeared to refine how they used their shared prey. Although all three species relied more heavily on pelagic fish, they shared these resources in ways that limited direct competition, whether by feeding on different proportions of prey, using different areas, or separating over time.

What these changes mean for a warming ocean

The study also highlights how each species is differently positioned to cope with change. Humpback whales occupied the highest trophic level and relied on a relatively narrow, fish-centered diet. Fin whales showed the greatest flexibility, with a broader diet and great variation between individuals, while minke whales fell in between, balancing a fish-based diet with notable individual differences. These contrasts help explain how the three species continue to coexist as conditions change.

“This ecosystem seems sufficiently productive and offers alternative prey distributed in space and time,” Tessier-Larivière said. “These conditions favor coexistence rather than one species supplanting and excluding others. »

As climate change reshapes marine ecosystems, the study suggests that adaptability could depend not only on what species eat, but also on how efficiently they share what’s left.

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