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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14539

The influence of fasting and opportunistic feeding on skin stable isotope values of migrating baleen whales

Kylie Owen*, Ross M. Thompson, David Donnelly, Michael Noad, Sarah J. Bury, Matthew H. Pinkerton, Rebecca Dunlop

*Corresponding author:

ABSTRACT: Many baleen whale species migrate between low-latitude breeding grounds and high-latitude feeding grounds, with increasing evidence that humpback whales (Megaptera novaeangliae) utilise supplemental feeding sites in temperate regions while migrating. The diet of whales while migrating is often unknown, and the impact that temperate feeding and/or fasting has on biochemical tracers used to investigate diet remains unclear. The aims of this study were to: (1) determine whether prey consumption at supplemental feeding sites could be detected by stable isotope analysis of skin; (2) obtain information on diet during migration; and (3) ascertain the impact of potential fasting on stable isotope values of baleen whales. Skin samples were taken from the eastern Australian humpback whale population on Antarctic feeding grounds, and two sites on the southward migration route (a sub-tropical site and a temperate site) across two years. At the sub-tropical site, ẟ13C and δ15N were consistent with the last place of foraging five months earlier. One exception to this was the higher (0.5‰) δ15N value in 2011, suggesting that in some years, potentially when blubber reserves are insufficient, δ15N may be influenced by fasting. In both years, skin ẟ13C and δ15N values at the temperate site were higher than those from the Antarctic and sub-tropical sites, indicating that a feeding signal from temperate zones had likely been incorporated, with whales feeding on fish and krill. Importantly, supplemental feeding while migrating could affect the interpretation of whale diet on feeding grounds if sampled early in the season.