This will disrupt ecosystems, as mesotherms are typically top predators that exert disproportionate control over species below them in the food chain, said Edward Snelling, co-author 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,” Snelling said in a news release. “These animals already operate on a tight energy budget and climate change is reducing their options even further.”
Using small sensors on a variety of fish, including basking sharks that weigh more than three tons, the researchers calculated how much heat the fish produce and lose in real time. From this, they calculated that a warm-bodied, one-ton shark may have difficulty staying in waters above 62.6° Fahrenheit (17° Celsius) without taking countermeasures. Uncovering these “hidden heat budgets” could prove critical to any hope of conserving them or mapping areas of protection, the researchers said.
In South Africa, what is at stake is both ecological and cultural. Here, white sharks have become a “sentinel species”: when their patterns change, it indicates a deeper change in the marine ecosystem.
While they were long sensationalized as feared predators, they have increasingly become icons of marine conservation and ecotourism, said Stephanie Nicolaides, a marine conservation researcher at the University of the Western Cape. “Many local and international conservation narratives now position the great white shark not as a villain, but as a keystone species essential to maintaining ocean health,” Nicolaides said.
However, the decline in white shark sightings in False Bay, Mossel Bay and Gansbaai is multifaceted. Although thermal relocation may contribute, its population decline It is also linked to a history of overfishing, shark nets and habitat destruction.
In fact, although warming waters increase the vulnerability of mesotherms around the world, other human-caused damage poses the greatest danger. “If we were to say what we urgently need to address for these animals, it’s the fisheries problem,” Payne said. “The most acute and urgent crisis facing these animals is overfishing and, particularly now, bycatch.”
Bycatch refers to fish and other marine animals unintentionally caught by fishermen using huge nets or longlines baited with thousands of hooks.
History, however, offers a grim precedent for physiological vulnerability itself. Fossils of extinct hot-bodied species, such as the infamous Megalodon shark, which reached almost 60 feet long— suggest that they suffered disproportionately during past ocean temperature rises, as they likely struggled for food to fuel their large, hot bodies.
“Today’s oceans are changing at unprecedented speeds,” Payne said. “Right now the alarm bells are ringing loudly.”
This article originally appeared in Insider climate newsa nonpartisan, nonprofit news organization covering climate, energy and the environment. Subscribe to their newsletter here.
