Great White Sharks Overheating as Climate Warms Oceans

Great white sharks and other mesothermic species face a significant threat from warming ocean temperatures, as their unique physiology demands more energy and makes them susceptible to overheating.

Great white sharks, alongside species like basking sharks, maintain body temperatures warmer than the surrounding water, an adaptation known as mesothermy. This evolutionary advantage, once crucial for enhanced predation and migration, now poses a substantial survival challenge as global oceans warm due to climate change. The oceans' iconic predators, benefiting from this internal furnace, now face an increasing cost.

This rare group, comprising less than 0.1% of all marine life, generates metabolic heat to elevate their core temperature above the ambient seawater. Mesothermic sharks, including great whites, use nearly four times more energy than cold-blooded fish. This heightened energy demand intensifies in warmer waters, especially as a fish grows larger and generates heat faster than it can shed, creating an overheating dilemma, according to a report published in the journal *Science*.

Rising ocean temperatures create a "double jeopardy" for these apex predators. They require increased caloric intake to fuel their internal heating mechanism, even as food sources dwindle, partly due to overfishing. Nick Payne, lead author and associate professor at Trinity College Dublin, emphasizes sharks cannot simply obtain more food as oceans warm.

As their environment heats, mesothermic sharks must slow down, alter blood flow, or dive into deeper, cooler waters to regulate body temperature. These behavioral shifts come with energy costs and potential impacts on hunting success, while suitable habitats for these mesotherm species shrink, especially during summer months, increasing competition for prey. Scientists will continue monitoring these populations and their movements to understand the long-term effects of ocean warming on these crucial marine predators.