Dave Edwards of West Cork Charters caught the 600lb, 8.5ft fish on Sunday, around three miles from where the boating firm is based in Courtmacsherry, south-west Ireland, Echo Live reported.

The fish—much larger than the average Atlantic bluefin tuna weighing 550lbs and 6.5ft in length—was so big the crew were only able to measure its size in the water.

The hulking creature weighs around the same as a 613lb bluefin tuna which sold for more than $3 million in Japan earlier this year.

West Cork Charters wrote on Facebook that the animal was the “first Bluefin tuna to be caught, tagged and released on The South Coast of Ireland, 102 inches in length.”

But as the trip was part of a catch and release initiative, Edwards set the tuna free. A further 14 boats on the south and west Irish coasts are taking part in the program which ends on October 15.

Edwards told Echo Live: “It’s getting close to the end of the season so we were beginning to lose hope that we would see any.”

Bluefin tuna are more common in Donegal Bay in north-west Ireland where they follow herring, Edwards told Echo Live.

“They are more unusual down here but tend to be much bigger when they do show up. This is the first one caught south of Donegal Bay this year and it really was a big fish,” he said.

Days before catching the enormous fish, Edwards and the West Cork Charters team hooked an even bigger tuna, which they believe measured up to 9-ft long. But it managed to escape when a top-of-the-range reel seized under pressure.

Edwards wrote on Facebook: “After losing the monster on Thursday I had to have a crack before the weather turned.”

The Inland Fisheries Ireland state agency worked for two years to develop the pilot Tuna Catch and Release Tagging (CHART) program. The 15 vessels authorized to participate come from Cork, Clare, Galway, Sligo and Donegal.

Before the launch, the crew members received training on how to handle and tag the fish while protecting their welfare.

It is hoped the initiative will “increase knowledge of the behaviour and abundance of Bluefin Tuna in Irish waters,” according to the agency.

Minister for Agriculture, Food and the Marine Michael Creed TD said in August: “This initiative will allow the Marine Institute and Inland Fisheries Ireland to collect valuable data on the migratory patterns of Bluefin tuna in Irish waters in a tightly controlled environment.”