Seasonal warming coincides with loss of epidermal diatoms 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 diatoms (microalgae) 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 slightly less diatom coverage than females overall, though the corresponding effect size was very small. Our results support the hypothesis that sea surface temperature can be a driving factor in the epidermal condition of cetaceans. This is consistent with a growing understanding of links between environmental conditions, movement behaviour, and individual health in wild populations.