In October 2020, surfers in Watergate Bay, Cornwall, were in just the right place at the right time to witness a fleeting spectacle.

An enormous bluefin tuna leapt clear out of the water – several times – landing with a huge splash just a few metres from their boards. It was one of an increasing number of surprising reports from people who have spotted these colossal fish, which had been missing from UK waters for decades.

The disappearance of bluefish tuna

Bluefin tuna used to be a much more common sight here. Big game fishermen hunted bluefins off Scarborough 90 years ago. But the animals disappeared in the 1960s, most likely wiped out by commercial fisheries in the north-east Atlantic. Then, in the early 2010s, bluefin tuna began staging a comeback in the English Channel and off the west coast of Ireland.

In the sushi trade, bluefins are famous for their meaty sashimi. At ceremonial new-year fish auctions in Tokyo, they sell for extortionate prices – albeit mainly as a marketing stunt. In 2019, a restaurateur paid over 300 million yen (close to £2 million) for a single bluefin. Prices aren’t so sky-high during the rest of the year, but demand has been high enough to drive intensive fishing.

Why have bluefish tuna returned to our oceans?

It was only when Atlantic bluefin numbers were in drastic decline that quotas were enforced, restricting the quantity that can be legally caught. This helped populations recover and is a likely reason why they are reappearing around the UK.

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Rising sea temperatures may also be involved. Bluefins prey on silvery fish, such as herring and anchovy, which are doing well in the warming waters of the Atlantic and could be luring tuna northwards. Catching bluefins is outlawed in British waters, although sport fisheries have obtained licences to tag and release them as part of a study.