A 3 meter long bluefin tuna was spotted off the English coast (Photo: Julie Hatcher/SWNS)

The world’s ‘most expensive’ fish has washed up dead in Britain, but it could bode well for the species’ return here, experts say.

The Atlantic bluefin tuna, which is over three meters long, was discovered in Kimmeridge, off the Dorset coast.

But conservationists say the sad sight could mean the species is making a comeback in British waters.

The Dorset Wildlife Trust said the main predators have disappeared from British seas since the 1960s, despite once being ‘abundant’ here.

But recently they have begun their return to the English Channel.

In 2019, a Japanese sushi magnate paid $3.1 million for a whopping 612-pound bluefin tuna, making it the most expensive tuna in the world.

“This is a beautiful species, one of the largest and fastest fish in the world,” said Julie Hatcher, the charity’s maritime awareness officer.

“The fact that this predator is back in our waters signals a healthier marine environment and also creates a true natural spectacle that has been missing from our coastal waters for far too long.”

Atlantic bluefin tuna has not been seen in British waters for decades (Photo: Getty)

On the reasons for the species’ disappearance, Ms Hatcher, a marine biologist, said: “It is thought this includes environmental changes – for example changes in the distribution of their prey species due to warming seas – overfishing of their prey species. – such as herring, mackerel and other pelagic fish – and this kind of direct targeting.”

Ms Hatcher said the species was regularly spotted in the seas around south-west England and along the west coasts of Wales and Scotland during the summer and autumn months.

She added: “When bluefin tuna feed on a ball of fish alongside dolphins and diving seabirds, it appears as if the sea is ‘boiling’ from all the activity on the surface.”

“However, we should not be complacent, because the threats that previously led to his long absence are still threats today.”

The bluefin tuna is one of the largest tuna species and can live up to 40 years.

It is currently illegal in Britain to catch tuna, commercially or privately, unless it is a small-scale scientific experiment.

The World Wildlife Fund calls tuna the ‘Ferrari of the ocean’ because they are sleek, powerful and built for speed.

There are several species of tuna, but bluefin tuna is the largest. They can grow up to 3 meters long and weigh up to 700 kilograms, more than a horse, and can swim long distances at up to 72 kilometers per hour.