Arctic humpback whales respond to nutritional opportunities before migration

Abstract

Rapid climate change in Arctic and Subarctic ecosystems is altering the spatio-temporal dynamics and abundance of resources. Whether highly mobile predators can respond and match their movements to changed resource peaks remains largely unclear. In the last decade, humpback whales (Megaptera novaeangliae) established a new foraging site in fjords of northern Norway during the winter, outside of their presumed foraging season. We used photographic matching to show that whales first sighted during fall in the Barents Sea foraged in northern Norway from late October to February, staying for up to three months and showing high inter-annual return rates (up to 82%). The number of identified whales increased steadily from 2010 to 2016. Genetic sexing and hormone profiling in both areas suggest higher proportions of pregnancy and a female bias in Norwegian waters. This indicates that the new site may be particularly important for pregnant females, likely to improve body condition before migration. Our results suggest that baleen whales can respond to nutritional opportunities along their migration pathways, in some cases by extending their feeding season. This supports the idea that migrating marine mammals can access novel prey resources as part of their response to environmental changes.