The world’s most expensive fish is threatened by climate change

3.1 million USD is the amount a billionaire paid for a bluefin tuna at an auction in Tokyo in 2019. The tuna weighed 278 kg, equivalent to a grizzly bear, and was the most expensive fish ever. is sold.

Tuna is the most commercially valuable fish family around the world, and bluefin tuna, often used in sushi and sashimi, is the most expensive species, according to Sarah Glaser, who heads the ocean futures team at the Foundation. World Wide Fund for Nature (WWF) USA.

One bluefin tuna is worth more than a ton of skipjack, the smallest and most abundant tuna species. Their high value led to overfishing, and the huge global demand for sushi severely depleted bluefin stocks, pushing the species toward extinction in 2010.

In recent years, bluefin tuna populations have experienced an incredible recovery after countries introduced sustainable fishing quotas and cracked down on illegal fishing. The International Union for Conservation of Nature (IUCN) classified Atlantic bluefin tuna from “endangered” to “least concern” in 2021. Meanwhile, Pacific bluefin tuna recovered to low levels. large numbers, exceeding international targets a decade ahead of schedule. Southern bluefin tuna are still endangered, but they are no longer in the “critically endangered” group on the IUCN Red List, according to Alessandro Buzzi, WWF’s tuna fisheries project manager.

But now, bluefin tuna is facing another big challenge: climate change. Research shows that bluefin tuna are extremely sensitive to temperature changes, with even small increases affecting their metabolism, reproduction and feeding abilities.

Scientists warn that changes to bluefin tuna could impact other marine wildlife as well as fishing communities. “We see bluefin tuna feeding in many unusual areas, for example in the North Sea, around Scandinavia and Iceland,” Buzzi said. “We have seen changes in migration patterns.”

Measuring 1.8 – 3 m long, bluefin tuna is the largest tuna in the world. They can live up to 40 years and are apex predators that hunt schools of fish such as herring and mackerel. This warm-blooded fish is among the fastest swimming animals on the planet. They migrate thousands of kilometers each year to lay eggs and hunt. But their migration patterns are starting to change.

As ocean temperatures warm, bluefin tuna move to colder waters. A recent study by the National Marine Fisheries Service found that large and small Atlantic bluefin tuna are moving farther north, to waters off the coast of Massachusetts, at speeds of 4 to 10 km. /year. Irish scientists noted that in 2019, six giant Atlantic bluefin tuna were pushed away from the migration route between Ireland and the Bay of Biscay or the mid-Atlantic ridge, swimming further north to Iceland. The new route is said to respond to the heat at sea.

Researchers are also concerned about the impact of rising temperatures on tuna spawning grounds. In June and July, Atlantic bluefin tuna flock to the Mediterranean to spawn, making this sea the world’s most important bluefin tuna fishery. The Mediterranean Sea is also a “climate hotspot”. By the end of the century, average ocean surface temperatures here are expected to increase by 1 – 3 degrees Celsius. Because there is not as much circulation as in larger ocean basins, the Mediterranean Sea will experience impacts much faster and larger from climate change.

Rising temperatures could push juvenile bluefin tuna out of the Mediterranean within the next 50 years, according to research from the University of Southampton in the UK. Research finds that ocean temperatures above 28 degrees Celsius negatively affect their metabolism and development. Bluefin tuna need warm water to spawn. Their eggs develop when the temperature reaches 20 degrees Celsius, but if the water is warmer than a certain threshold (28 degrees Celsius), their metabolism begins to decrease.

Temperatures in the Mediterranean surpassed the above critical threshold in August 2024 when daily sea surface temperatures reached a record 28.45 degrees Celsius. Research results show that bluefin tuna spend most of their time in The upper 20 m of the water column.

As ocean temperatures increase, bluefin tuna will move their nursery areas away from the Mediterranean, to colder waters like the Bay of Biscay. Juvenile tuna can be caught bycatch in anchovy and sardine fisheries in this bay.