An Irish fisherman caught an 8ft long, 600lb bluefin tuna worth €3 million and then let it go.

The massive fish was caught off the cost of west Cork by Dave Edwards, of West Cork Charters in Courtmacsherry.

The incredible catch was part of an ongoing catch and release program aimed at establishing population numbers for the fish in the north east Atlantic, The Irish Post reports.

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Edwards, with the help of fellow anglers Darren O’Sullivan and Henk Veldman, caught the fish about three miles south of his base in Courtmacsherry.

"They are much more common up in Donegal Bay where they follow the herring," he said.

"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."

Publiée par West Cork Charters sur Dimanche 22 septembre 2019

The fish is the largest specimen caught in Irish waters this year and is about as big as Atlantic bluefin tunas tend to get, according to Echo Live.

Edwards’ is one of 15 boats along the south and west coasts of Ireland taking part in the catch and release program, which runs from August 15 to October 15.

"It's getting close to the end of the season so we were beginning to lose hope that we would see any," said Edwards.

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"Then on Sunday we had a huge fish on the reel that must have been closer to 10 feet in length but after a two and a half hours it got away. We knew they were out there then though and so it turned out when we managed to tag this one."

The enormous fish couldn’t be landed and had to be measured in the water before being tagged and released.

A stock photo of a bluefin tuna.iStock/Getty Images