ABSTRACT
Maintaining a stable core body temperature is essential for endotherms. Cetaceans live in a highly thermally conductive medium, requiring special adaptations to reduce heat loss and maintain homeothermy. We employed a combination of aerial photogrammetry and existing data sources to estimate heat loss rates in five sympatric cetaceans of varying sizes, inhabiting the sub-arctic waters (∼3.7°C) of NE-Iceland: harbour porpoises (Phocoena phocoena, 1.0–1.6 m, n=50), white-beaked dolphins (Lagenorhynchus albirostris, 1.1–2.9 m, n=294), minke whales (Balaenoptera acutorostrata, 4.4–8.6 m, n=30), humpback whales (Megaptera novaeangliae, 6.0–14.2 m, n=282) and blue whales (Balaenoptera musculus, 13.2–24.2 m, n=29). Further, we investigated the effect of body size (length), body shape (surface-area-to-volume ratio, SVR), body temperature and blubber thermal conductivity and thickness on heat loss for all species. Smaller species had higher volume-specific heat loss compared with larger species due to their higher SVRs, a fundamental consequence of scaling. Apart from body size, blubber thickness had the largest effect on heat loss, followed by thermal conductivity. Smaller cetaceans seem to rely primarily on physiological and morphological adaptations to reduce heat loss, such as increased blubber thickness and lower thermal conductivity, whereas larger species offset heat loss by having larger bodies and lower SVRs. Our findings provide valuable insights into the thermal biology of these species and its implications for habitat use and prey requirements.
Footnotes
Author contributions
Conceptualization: M.G., M.H.R., F.C.; Data curation: M.G., A.P., S.N.S.R., D.S., Z.S., M.J.; Formal analysis: M.G., F.C.; Funding acquisition: M.G., M.H.R., F.C.; Investigation: M.G., A.P., S.N.S.R., D.S., M.J.; Methodology: M.G., F.C.; Project administration: M.G., M.H.R., F.C.; Resources: M.G., M.H.R., M.R.I., G.M.S., S.D.H., V.C., P.J.C., Y.I., D.T., F.C.; Supervision: M.H.R., F.C.; Validation: M.G., F.C.; Visualization: M.G.; Writing – original draft: M.G., M.H.R., F.C.; Writing – review & editing: M.G., M.H.R., A.P., S.N.S.R., D.S., Z.S., M.J., M.R.I., G.M.S., S.D.H., V.C., P.J.C., Y.I., D.T., F.C.
Funding
M.G. received funding from the University of Iceland’s Doctoral Grants Fund (The Eimskip University Fund/Háskólasjóður Eimskipafélags Íslands) and The Company of Biologists Travelling Fellowship. A.P., S.N.S.R., D.S. and M.J. received support from the Erasmus+ Programme for Traineeships during data collection. M.H.R. received funding from the University of Iceland Research Fund to cover the fieldwork expenses. The sampling of bycaught animals in Iceland was funded by the Marine and Freshwater Research Institute.
Data availability
The data that support the results of this study are available from the corresponding author upon request.
