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Bluefin tuna and shark
An essential species for both human nutrition and marine food chains, tuna has a fascinating peculiarity: it is one of the few warm-blooded fish. Unlike almost all fish, whose body temperature follows that of the water, some tuna, swordfish and sharks like the mako or white shark can maintain a higher internal temperature thanks to a highly efficient heat exchange system.
This mechanism gives them a decisive advantage. It enables them to swim faster, hunt better and even explore cold waters, right up to the polar zones. Bluefin tuna born in the Balearic Islands can pursue herring as far as Iceland. But as ocean temperatures rise, this superpower becomes a handicap.
Ever-increasing needs
Researchers have shown that a warm-blooded fish consumes up to 3.8 times more energy than a cold-blooded fish. And the warmer the water, the greater its needs. A rise of 10°C can double its metabolism, forcing it to eat more. Yet a tuna may already consume the equivalent of its own weight every day. Eventually, warming seas could starve them out.
The study also estimates that beyond a certain threshold, the water is no longer sufficient to cool these animals. For basking sharks, for example, overheating starts at 17°C. When the water becomes too warm, tuna and shark have few options: dive deeper, migrate to cooler areas or slow down their swimming to limit heat production.
They are therefore under double stress: heat forces them to modify their behavior while increasing their energy requirements. An additional pressure on species already weakened by overfishing. The study reminds us that protecting tuna depends not only on quotas, but also on climate change. Eating tuna in moderation, and preferring low-impact fishing methods such as line fishing, therefore becomes a more responsible choice.
