GoKawiilThe evolutionary edge that fueled great white shark dominance for millions of years could soon become its greatest downfall.
The ocean’s most iconic predators maintain warmer body temperatures than the surrounding seawater and are paying an increasingly steep price for it. As the oceans warm due to climate change, they now face the risk of potentially fatal overheating, according to a new study in Science.
Several large tuna species and sharks, known as “mesothermic” species for the way their bodies run hot, require more fuel to maintain their temperature and are thus confronting a “double jeopardy” of warming oceans and declining food, mainly from overfishing. As water temperatures climb, these species will be forced to relocate to cooler waters.
“If you’re a shark, you can’t just pop down to the supermarket and buy more food,” said Nick Payne, lead author and associate professor at Trinity College Dublin in Ireland. “We’re seeing animals move with climate change in every biome on land and in the sea; this is just another example of that mechanism.”
From South Africa’s powerful great whites to Ireland’s filter-feeding basking sharks, these mesotherms burn nearly four times as much energy as their cold-blooded counterparts, whose body temperatures match the surrounding water. As oceans warm, these species must slow down, alter their blood flow or dive to cooler temperatures, all while hunting for an ever-dwindling food supply.
A rare group comprising fewer than 0.1 percent of all marine life, mesothermic fishes — also including thresher and porbeagle sharks — trap metabolic heat to keep their bodies warmer than surrounding seawater. This has been evolutionarily key to enabling higher swimming speeds, enhanced predation, and their long-distance migrations.
However, as fish grow larger, their bodies generate heat faster than they can shed it. This mismatch — driven by the physics of surface area and heat retention — triggers the overheating dilemma in warmer waters.
While some species like Atlantic bluefin tuna can temporarily boost their heat loss or dive to colder waters, the suitable habitats for mesotherm species will shrink as larger swaths of oceans become inhospitably hot. This will be especially the case during summer months when sharks will experience increased competition for prey.
This will disrupt ecosystems as mesotherms are typically apex predators that exert disproportionate control on species below them in the food chain, said Edward Snelling, coauthor and physiologist at the University of Pretoria.
“These species are being pushed closer to their physiological limits, which could have consequences for where they can live and how they survive,” said Snelling in a press release. “These animals are already operating on a tight energy budget, and climate change is narrowing their options even further.”
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