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28-Year Study Finds Gulf of St. Lawrence Whales Shift From Krill to Fish as Diets Diverge

Researchers tie the shift to warming-linked declines in Arctic krill.

A humpback whale's tail emerges from the water on the St. Lawrence River. As climate change impacts the kinds of prey fish available, Canadian research shows that different species of whales are shifting their diets and may be sharing food resources.
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Overview

  • The analysis used stable carbon and nitrogen isotope ratios from 1,110 skin samples collected from fin, humpback and minke whales between 1992 and 2019.
  • Across cooler, near-average and warmer periods, all three species moved toward pelagic fish such as capelin, herring, mackerel and sand lance, with fin whales showing the largest departure from krill-dominated diets.
  • Niche overlap shrank in the 2010s, dropping for humpback–minke from about 56% to 9% and for fin–minke from roughly 42% to 29%, indicating increased resource partitioning.
  • Humpbacks maintained a relatively narrow, fish-centered niche, fins displayed the greatest flexibility, and minkes balanced fish feeding with some krill use.
  • Authors report no competitive exclusion and recommend ongoing trophic monitoring and climate-informed fisheries and marine protected area planning, while noting isotopes cannot pinpoint feeding locations or exact prey proportions.