Great white sharks are overheating

This would disrupt ecosystems, said co-author and physiologist Edward Snelling of the University of Pretoria, because mesotherms are often apex predators that exert disproportionate control over species below them in the food chain.

“These species are being pushed to their physiological limits, which may have consequences for where and how they survive,” Snelling said in the release. “These animals already have a tight energy budget, and climate change further narrows their options.”

Researchers used tiny sensors on a range of fish, including basking sharks that weigh more than three tons, to instantly calculate how much heat the fish produce and lose. From this, they calculated that without countermeasures, a one-ton warm-bodied shark might have a hard time staying in waters above 62.6 degrees Fahrenheit (17 degrees Celsius). Researchers say discovering these “hidden heat budgets” is crucial to any hope of protecting them or mapping protected areas.

In South Africa, what is at stake is ecology and culture. Here, great white sharks have become a “sentinel species”: when their patterns change, it signals deeper shifts in marine ecosystems.

Stephanie Nicolaides, a marine conservation researcher at the University of the Western Cape, said that while they had long been considered feared predators, they were increasingly becoming a symbol of marine conservation and ecotourism. “Many local and international conservation narratives now no longer position great white sharks as villains, but instead view them as a keystone species necessary to maintain ocean health,” Nicolaides said.

However, the decline in great white shark sightings in False Bay, Mossel Bay and Gansbaai is multifaceted. Although thermal migration may be a factor, they population decline It’s also linked to a history of overfishing, shark nets and habitat destruction.

Indeed, while ocean warming increases the vulnerability of mesotherms worldwide, it is other anthropogenic hazards that pose the greatest danger. “If we had to say there’s one thing we need to address urgently for these animals, it’s fishing,” Payne said. “The most serious and urgent crisis facing these animals is overfishing, especially now bycatch.”

Bycatch refers to fish and other marine animals that are unintentionally caught by fishermen using large nets or long lines equipped with thousands of hooks.

Yet history provides a grim precedent for physiological vulnerability itself. Fossils of extinct warm-bodied species, such as the infamous Megalodon, have almost arrived 60 feet long– suggests they suffered disproportionately during past periods of rising ocean temperatures because they may have had difficulty obtaining food to fuel their large, warm bodies.

“Today’s ocean is changing at an unprecedented rate,” Payne said. “At this moment, alarm bells are ringing.”

This article was originally published in Inside climate newsa nonprofit, nonpartisan news organization covering climate, energy and the environment. Subscribe to their newsletter here.