Elevated body temperatures of adult female leopard sharks, Triakis semifasciata, while aggregating in shallow nearshore embayments:: Evidence for behavioral thermoregulation?

The leopard shark, Triakis semifasciata, is an abundant nearshore elasmobranch, ranging from Baja California, Mexico to Oregon, USA. Mature female leopard sharks have been observed aggregating in shallow embayments throughout California; however, it is unclear why only females aggregate in these shallow areas. The goal of this study was to determine if mature female leopard sharks selectively occupy the warmest areas of a shallow embayment, if free-ranging leopard sharks' body temperatures are significantly warmer during the day than at night, and to quantify temporal use of these shallow habitats. Visual observations of sharks' fine-scale movements within the shallows of Big Fisherman's Cove Marine Life Refuge (Santa Catalina Island) aggregation site indicated that sharks preferred the warmest areas of the embayment and moved to warmer locations over the course of the day (p < 0.05). Active and passive acoustic tracking, along with archival transponder technology (Vemco: V 13, V13-R256, VX32TP-CHAT tags respectively) of 16 sharks caught and tagged within this aggregation were used to monitor core body temperature, swimming depth, and movements. Sharks had significantly higher core body temperatures in the late afternoon (1700 h-2000 h) during the summer, showed increased fidelity to thermal refuges during the day and increased movement away from these refuges at night (chi(2), p < 0.05). Seasonal variations in warm, shallow water usage were also observed. Elevated core body temperature of mature female leopard sharks using warm shallow embayments will likely augment metabolic and physiological functions such as digestion, somatic growth, and possibly reproduction. (c) 2007 Elsevier B.V. All rights reserved.