The first was caught just three days earlier, weighing 18lbs lighter on another of Phatcat’s 11-hour trips.
On Sunday, the group of six took it in turns to reel the shark in as it did its best to escape, 17 miles from shore.
Mr Thomas said: “I couldn’t believe it when I was told the shark was the biggest caught in Welsh waters.
“It certainly didn’t make it easy for me, taking over five hours to reel it in. I was really tired by the end but it was all worth it.
Thresher sharks are usually solitary creatures who keep themselves to themselves, and can be seen jumping out of the water like a dolphin.
Craig Deans, Phatcat Charters skipper, used a trusted formula of measuring the length and girth of the fish to calculate its weight to record the mammoth catch.
“It was a very unusual catch,” he said.
“Normally when you get a shark, it takes about two hours to reel it in. Its so rare. Its a big thing for a fisherman to catch one.
“It was definitely the best catch and the best day for me. We were all buzzing on the boat. We were like schoolkids. ”
Mr Deans said Mr Thomas had to let someone else take the reins on the catch after three and a half hours when he became too tired to carry on.
It was he, however, who managed to get the shark onboard in the end.
“It was very unusual to get one and we’ve had two in the same week,” Mr Deans said.
“You see one jumping out of the water now and then but in the angling world, to catch a shark, is a big thing. ”
The skipper, who has been fishing around England and Wales for 25 years, is expecting to see a lot more thresher sharks off the coast of Milford Haven, as commercial fishing of porbeagle sharks has been stopped.
“I just think these fish were getting culled as a by-product as well and it has made a lot of difference where they’ve stopped it,” he said.
“It’s been really good this season already.
“I’ve been shark fishing out there for two or three years now the fishing off Milford Haven is the best in Europe.
Phatcat has a strict catch and release policy when shark fishing to conserve stocks and to treat the animals with respect, so let the shark swim off after recording the find.
Barb-free hooks and a special hook extraction tool ensure the release of the shark is as pain-free as possible.
“He was still full of beans when we got him on the boat,” Mr Deans added.
“There was no damage to the fish and as soon as we put it back in the water, he had plenty of life in him after that.
“It’s been a good week for Welsh anglers, with the record being broken and topped again in the space of three days.
“Wales really is becoming the hotspot for shark fishing, standing up to tough competition from other parts of Europe and this latest catch proves just that.”