Multispecies thermal dynamics of air-exposed ectothermic sharks and its implications for fisheries conservation

Body temperature is a crucial component of thermoregulation, being strongly linked to variables such as energy flow, metabolic rates, activity patterns and resilience. With exception of lamnid sharks, elasmobranchs are classified as ectothermic, depending on ambient temperature for heat modulation. Despite often being removed from the water during fisheries interactions, the known effects of air exposure on sharks are limited to the hypoxia experienced. Comparatively little is known about the potential effects of changing ambient temperatures and solar radiation experienced by sharks during air exposure, and if such scenarios may compromise their thermal dynamics and survival. Here we used infrared thermography (IRT) to measure external body temperature of 10 different shark species (N = 62), ranging in size from 106 to 340 cm total length, experimentally exposed to air. We tested the hypothesis that all individuals would exhibit body surface temperature increases when air-exposed, with temperature uniformly distributed across the body surface regardless of species. Our results did not support this hypothesis. Although ectothermic, sharks exhibited significant species-specific variations in heat distribution and warming along the body surface. Moreover, these thermal patterns were significantly impacted by both environmental factors (water temperature at capture) as well as biological traits (shark size and body region). Multivariate analyses separated the 10-shark species into five groups according to the influences of shark body size, body region and water temperature on variations in the thermal profiles detected. We discuss the potential physiological, ecological and conservation implications of these findings.