Rikardsen, A. H. | Search bioRxiv

bioRxiv2022

Arctic humpback whales respond to nutritional opportunities before migration

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.

animal behavior and cognition↗

bioRxiv2022

Genetic stock identification reveals greater use of an oceanic feeding ground around the Faroe Islands by multi-sea winter Atlantic salmon.

There is a general paucity of knowledge regards spatial variation in marine resource use for many taxa, even those of high socio-economic importance such as Atlantic salmon. While it is known that the oceans around the Faroe Islands support a salmon feeding ground, the relative use of this feeding ground by different age classes across different stocks remains largely unexplored. Using a combination of genetic stock assignment and run-reconstruction models, we observed a consistent pattern whereby the proportion of multi-sea winter (MSW) salmon for a given reporting group was substantially greater around the Faroes than the MSW proportion for that reporting groups among the prefisheries abundance. Surprisingly, MSW fish from Ireland and UK were as likely to occur around the Faroes as were MSW fish from more north-eastern regions such as the Teno river and the Barents and White Seas. MSW fish from Southern Norway were the most likely to be caught at the Faroes. While 1SW salmon from Ireland and UK as well as from Southern Norway occurred at similar rates around the Faroes, 1SW fish from more north-eastern reporting groups were nearly entirely absent from the same feeding ground. In combination with previous studies that examine the marine distribution of Atlantic salmon, our results strongly indicate that the oceans around the Faroes play host to a predominantly MSW salmon feeding ground and that use of this resource varies both within the age classes of a given stock as well as between different stocks. Furthermore, these results suggest that MSW fish from certain stocks might preferentially undertake migrations to the Faroes. Variation in spatial resource use may help to buffer salmon stocks against localised negative changes in marine conditions.

ecology↗