Thermal performance and activation energy explain flexible thermal habitat use in great hammerhead sharks

Understanding the relationship between animal performance and temperature is a pressing issue in the face of climate change because it has implications for changes to distribution, population dynamics and species interactions. We used accelerometers to build a thermal performance curve (TPC) for a large marine predator, the great hammerhead (Sphyrna mokarran), to explain this species' catch rates and thermal habitat use in the wild. Analysis of performance data captured by accelerometers deployed on nine sharks estimated great hammerheads have a thermal optimum (Topt) of 29.3°C. However, the TPC had a low activation energy compared with those of other large sharks, enabling high performance across a relatively broad temperature range. Analysis of catch data from surveys off the Gulf coast of Florida showed most sharks were caught in months where sea surface temperatures average 29-30°C, when large teleost prey are abundant. Satellite telemetry data showed sharks encountered average daily minimum and maximum temperatures below our estimated Topt, 24.7±1.6°C and 26.5±1.7°C, respectively. Relatively low activation energy (0.38±0.07 eV) likely enables great hammerheads to take advantage of seasonal prey pulses during both summer and winter by maintaining high performance outside Topt. While activity-based TPCs can provide a mechanistic link to migration patterns and relative abundance, they may also explain the ability of some predators to take advantage of seasonal, fast-moving prey at the lower limits of optimal thermal conditions.