Seasonal warming drives epidermal shedding in northern bottlenose whales

Animals move for access to better conditions, resources, or mating opportunities. However, evidence from cetaceans suggests that some long-distance travel to warmer waters may be primarily related to physiological maintenance, specifically the shedding of epidermal diatoms and parasites. Here we test this “physiological maintenance hypothesis” for cetacean movement from a new angle, asking whether changes in temperature influence epidermal shedding in a localized, resident population. We used a long-term dataset of northern bottlenose whales (Hyperoodon ampullatus) on the Scotian Shelf to test whether large seasonal changes in sea surface temperature predict levels of diatom coverage. Generalized linear mixed models and generalized additive mixed models showed that a seasonal change in SST from 8° to 21° Celsius was associated with a decrease in diatom coverage from approximately 26% to 11%. We also found that males had less diatom coverage than females overall, and that diatom coverage tended to increase with estimated (minimum) age. Epidermal shedding is important in health maintenance for cetaceans as diatoms and skin lesions are thought to be linked to immune function. Our results support the hypothesis that health can be a driving factor in animal movements and demonstrates how environmental change can have major effects on behaviour.