Seasonal warming drives epidermal shedding in northern bottlenose whales

Charlotte Riddle, Chad Steverding, Laura J Feyrer, Hal Whitehead, Sam Froman Walmsley

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.