Marine mesotherms are able to occupy broader thermal niches than ectotherms; however, this means they must exhibit greater tolerance to diverse environmental conditions across the ocean. Knowledge remains limited about how differences in environmental conditions within occupied habitats affect the bioenergetics of mesotherms and associated ecological traits. Here, we report that leatherback turtles (Dermochelys coriacea) migrating across the North Pacific changed their dive behavior regionally, possibly in response to changes in sea surface temperature and prey abundance. Our results demonstrate that dives became deeper when the surface water was warmer, presumably because leatherbacks dive to deep cold waters to avoid overheating. Moreover, the patterns of presumed foraging dives indicate that leatherbacks engage in behavioral thermoregulation in warmer foraging regions, which perhaps limit the time available for foraging activity. In contrast, mesothermy allows leatherbacks to spend more time foraging in cool-temperate regions. However, it might not produce greater reproductive output due to additional migration cost to these areas, which are more distant from their nesting beaches. Our results highlight that mesothermy might not provide a direct fitness advantage to all individual leatherback turtles; rather, it affords a species-level fitness advantage by allowing a greater diversity of habitats to be utilized.

We obtained this dataset of dive behavior of 16 leatherback turtles migrating across the North Pacific by Satellite relay data logger.