Meeting Abstract
Swordfish (Xiphias gladius ) are large pelagic predators known for their capacity to undergo extensive diurnal diving movements. Swordfish, like tunas and lamnid sharks, have internalized aerobic red, locomotor muscle (RM) and retia, albeit simplistic; this suggests that swordfish are capable of regional endothermy, or at the very least capable of modulating heat transfer rates during vertical movement. This study used data obtained from modified archival tags that allowed the simultaneous measurement of ambient and deep-body (e.g., RM) temperatures to examine the rates of heat balance (i.e., body cooling and warming) in free swimming swordfish (n=6). Newtonian heat transfer models in which the whole-body thermal conductivity of swordfish (k), was constant, variable, or variable based on water and swordfish body temperatures were used to assess changes in heat balance during descents, ascents, and surface intervals. While the models adequately described differential heating and cooling rates for dive and surface intervals, the best-fit model was largely dependent on swordfish behavior (e.g, deep diving, basking, surface oriented). Although, K values obtained in this study were within the range of those for other endothermic fishes, swordfish RM appears capable of operating at very low temperatures for prolonged periods of time. Future work will develop more complex heat transfer models that incorporate a suite of important parameters that directly affect heat transfer (i.e. heat exchanger efficiency, bulk blood flow, metabolic heat production) to assess the potential ability of swordfish to physiologically thermoregulate.
