The evolutionary cheat code that made great white sharks the undisputed champions of the ocean for millions of years is now threatening to cook them from the inside out. A new report in the journal Science reveals that these iconic predators, along with several large tuna species, are mesothermic, meaning they maintain warmer body temperatures than the surrounding seawater. This biological advantage is becoming a liability as climate change warms the oceans, putting them at risk of potentially fatal overheating.
These mesothermic species, a rare club comprising fewer than 0.1 percent of all marine life that also includes thresher and porbeagle sharks, are facing a 'double jeopardy.' They burn nearly four times as much energy as their cold-blooded counterparts to stay warm, and now they must do so in increasingly hot water while hunting for an ever-dwindling food supply, thanks largely to overfishing. As lead author Nick Payne, an associate professor at Trinity College Dublin, Ireland, wryly noted, 'If you're a shark, you can't just pop down to the supermarket and buy more food.'
The physics are unforgiving. As these fish grow larger, their bodies generate heat faster than they can shed it, a mismatch driven by the relationship between surface area and heat retention. From South Africa's great whites to Ireland's basking sharks, they are now forced to slow down, alter their blood flow, or dive to cooler depths just to avoid boiling in their own skins. All of these coping mechanisms come with a significant energy cost while they're already struggling to find enough to eat.
The future looks like a game of oceanic musical chairs with fewer and fewer cool seats. While some species, like the Atlantic bluefin tuna, can temporarily boost heat loss or seek deeper, colder waters, the suitable habitats for all these mesotherms will shrink as larger swaths of the ocean become inhospitably hot. This squeeze will be especially intense during summer months, turning the hunt for prey into an overheated, high-stakes competition where the losers literally overheat.