Marine Biologists Identify Critical Overheating Thresholds for High Performance Mesothermic Sharks and Tuna Species

Trinity College Dublin research shows warm-bodied sharks and tuna burn 4x more energy, placing them in "double jeopardy" as ocean temperatures rise.

By: AXL Media

Published: Apr 17, 2026, 7:43 AM EDT

Source: Information for this report was sourced from Trinity College Dublin

The Physiological Cost of High Performance Hunting

A study published in the journal Science has quantified the massive energy requirements of the ocean's most formidable predators, identifying a significant vulnerability in their specialized physiology. Mesothermic fishes, a rare group representing less than 0.1% of all fish species, possess the unique ability to keep parts of their bodies warmer than the surrounding seawater. While this trait enables superior swimming speeds and long-distance migrations, it comes with a steep metabolic price. Researchers found that these animals burn approximately 3.8 times more energy than ectothermic, or cold-blooded, fish of a similar size. This heightened demand creates a precarious biological budget that is increasingly difficult to maintain as global sea temperatures climb.

Theoretical Thresholds and the Overheating Dilemma

The research team, which included scientists from the University of Pretoria, established "heat-balance thresholds" to predict when large fish can no longer shed heat effectively. Because larger bodies retain heat more efficiently due to basic geometry and physics, high metabolic rates amplify the risk of internal temperature spikes. For example, a one-tonne warm-bodied shark may struggle to maintain a stable body temperature in waters exceeding 17°C. When these thresholds are crossed, predators are forced to slow down, alter their blood flow, or dive into deeper, cooler waters. These behavioral shifts often pull the animals away from their primary hunting grounds, reducing their overall predatory performance and efficiency.

Biologging Data From Marine Giants

To capture these metabolic measurements in free-swimming animals, scientists utilized advanced biologging technology. Small sensors were attached to various species, including basking sharks weighing up to 3.5 tonnes, to record real-time body and water temperatures. First author Dr. Nicholas Payne noted that a 10°C increase in body temperature more than doubles a fish's routine metabolic rate. This data suggests that as surface waters warm, these predators must consume significantly more food just to sustain their basic lifestyle. The combination of high-resolution sensor data and laboratory measurements provides the first comprehensive framework for understanding the thermal constraints of large marine giants.