Conflicting Physiological Challenges between Thermoregulation and Diving Energetics in Elephant Seals

Deep-diving marine mammals face significant thermoregulatory challenges living in a thermally-conductive environment with steep temperature gradients. They are well-insulated to conserve heat, but dissipating heat may result in a conflict between the dive response and thermoregulation as both are affected by the regulation of peripheral blood flow. To coordinate these physiological adaptations, marine mammals may have a temporally-delayed thermoregulatory response during normal diving behavior. We assessed this hypothesis by equipping freely-diving juvenile northern elephant seals (Mirounga angustirostris; n=2) with custom-built heat flux biologgers over short at-sea trips. Skin temperature (ST) and heat flux (HF) measurements from two sensors were analyzed relative to diving behavior and water temperature. ST remained within -0.2 to 2.7°C of water temperature but significant differences between the axilla and flank in both ST and HF suggests nonuniform heat dissipation. HF patterns revealed heat loss begins early in the descent at depths <20 m and continues throughout most of the dive at an average rate of 62.7 W/m². The transition to heat gain occurs towards the end of the ascent, first through the flank followed by the axilla, reaching mean peak values of 109.8 W/m² at the surface. While average HF during the dive showed weak and no correlation at the axilla and flank, respectively, with dive depth and duration, average post-dive HF at both locations was positively correlated with both dive depth and duration. These results support our hypothesis and suggest peripheral cooling prevents conflict with the dive response and may be partially compensated by post-dive heat gain in surface waters particularly for longer dives. Work is continuing using modified HF biologgers that incorporate additional measurements to explore the mechanisms underlying these thermoregulatory responses and compare physiological plasticity during normal and disturbed diving behavior.