| Summary: | In the Atlantic Arctic, bowhead whales ( Balaena mysticetus ) were nearly exterminated by European whalers between the 17th and 19th centuries. The collapse of the East Greenland-Svalbard-Barents Sea population, from an estimated 50,000 to a few hundred individuals, drastically reduced predation on mesozooplankton. Here, we tested the hypothesis that this event strongly favoured the demography of the little auk ( Alle alle ), a zooplanktivorous feeder competitor of bowhead whales, and the most abundant seabird in the Arctic. To reconstruct pre-whaling little auk abundance, we modelled trophic niche overlap between the two species using deterministic simulations of mesozooplankton spatial distribution. We estimated a 70% increase in Northeast Atlantic Arctic little auk populations following bowhead whaling, from 2.8 million to 4.8 million breeding pairs. While corresponding to a major population increase, this is far less than predicted by previous studies. Our study illustrates a trophic shift resulting from the near extirpation of a marine megafauna species, and the methodological framework we developed opens up new opportunities for marine trophic modelling. Funding provided by: Institut Polaire Français Paul Émile Victor ROR ID: https://ror.org/011ed2d57 Award Number:
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