Escalating competition in changing seas: baleen whales exploit killer whale prey herding.

Climate change and other anthropogenic pressures are rapidly reshaping marine ecosystems, altering prey availability and predator interactions. Yet empirical evidence of how these relationships shift under changing conditions remains scarce. Drawing on over a decade of monitoring in a subarctic fjord system, we provide a rare insight into these dynamics. In northern Norway, the winter aggregation of herring (Clupea harengus) and their primary predator, the killer whale (Orcinus orca), has shifted northward under the combined influence of climate change and fishing pressure. This redistribution has brought baleen whales into the same foraging grounds, leading to direct interference competition. Humpback (Megaptera novaeangliae) and fin whales (Balaenoptera physalus) frequently intrude into killer whale carousel feeding events, exploiting dense, shallow prey patches optimized for lunge feeding. Such intrusions often end hunts prematurely, imposing energetic costs on killer whales. Meanwhile, the rapid growth of whale-watching tourism in these fjords further disrupts foraging activity. Integrating unpublished data and existing literature, this article highlights the asymmetric energetic costs and benefits arising from these emerging interactions; processes likely widespread, yet still largely undetected in other marine ecosystems. This article is part of the theme issue 'Multi-predator feeding aggregations in the pelagic'.