Dublin, Ireland – New research shows that some of the ocean’s most powerful predators are under growing pressure as warming seas and rising energy demands push them toward their physiological limits.

The study, led by scientists at Trinity College Dublin in collaboration with the University of Pretoria’s Faculty of Veterinary Science, focuses on warm-bodied fish such as tunas and certain sharks, including great white sharks and basking sharks. It finds that these animals burn nearly four times more energy than cold-blooded fish.

Researchers describe this as a “double jeopardy” scenario, where high-energy lifestyles combine with warming oceans and shrinking food availability, increasing stress on these species.

The findings were published in the journal Science and focus on mesothermic fish, a rare group making up fewer than 0.1% of fish species. These animals can retain metabolic heat, allowing faster swimming and long-distance migration, but at a significant energy cost.

To measure this, scientists used biologging sensors to track body and water temperatures in free-swimming fish, including large basking sharks weighing up to 3.5 tonnes, alongside laboratory data from smaller species.

Dr Nicholas Payne, the study’s first author, said warm-bodied fishes use about 3.8 times more energy than similar cold-blooded species. He also noted that a 10°C increase in body temperature more than doubles routine metabolic rates, meaning these predators must consume far more food.

He added that larger bodies generate heat faster than they can release it, creating a physical mismatch that increases overheating risk.

Professor Andrew Jackson, the senior author, explained that the team developed “heat-balance thresholds,” identifying water temperatures above which large fish cannot maintain stable body temperatures. For a 1-tonne warm-bodied shark, this limit is around 17°C.

Above these limits, fish must slow down, change blood flow, or dive into deeper waters, which can reduce their ability to hunt effectively.

The research also helps explain why large fish are often found in cooler regions, at higher latitudes, or in deeper waters, and why many migrate seasonally to track suitable temperatures.

Scientists warn that future ocean warming will likely shrink suitable habitats for these species, especially in summer, placing additional strain even on adaptable animals like Atlantic bluefin tuna.

Researchers say these animals already operate on tight energy budgets, and climate change is further restricting their survival options. Fossil evidence, including extinct species like Megalodon, suggests large warm-bodied marine predators have been highly vulnerable during past climate shifts.

The study concludes that understanding the hidden energy and heat limits of marine predators is essential for predicting how ocean ecosystems will change as global temperatures continue to rise.

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