London - More than an hour into the gruelling tussle, angler Mark Nelson wondered if his fishing line was hooked into a submarine.
But it was this 28-stone shark with gleaming, razor-sharp teeth that finally burst from the water off the coast of Cornwall, giving the 45-year-old the catch of a lifetime.
The builder managed to measure up the porbeagle shark – half the length of his boat – and confirm it as one of the biggest ever caught in British waters.
In scenes reminiscent of the film Jaws, Mr Nelson spent 90 minutes struggling with the 9ft (about 3m) fish but it was too big to pull aboard, so he measured and photographed it before releasing it.
The skipper of the charter boat Jerry Rogers – who took the pictures as Mr Nelson brought in his catch – calculated the weight of the porbeagle using its length and girth, working out it would have weighed more than 400lbs.
Mr Nelson, from Mountain Ash in South Wales, made the catch four miles off Boscastle.
He said: “I had caught a 300lb shark the day before and I was over the moon with that one. But it felt like I had hooked into a submarine in comparison when I caught the bigger one the next day.
“It took me an hour and a half to get it to the boat. It had so much power and aggression. My arms were aching a lot afterwards and had pins and needles.”
Porbeagles are the most common species of shark found in British waters, along with blue sharks, and are related to great whites. However, they are not a threat to humans with only three recorded attacks – and none of them fatal.
The largest shark caught in UK waters was a 14ft thresher shark weighing more than 550lbs, off the Isle of Wight in 2013.
Skipper Mr Rogers, 47, said: “Not a lot of people catch porbeagles but I have a lot of experience and know the right areas to look for them. They aren’t for the novice angler and I think Mark felt pretty beaten up afterwards.”
Porbeagle sharks are found all around the UK, usually at least ten miles offshore, but sometimes venture further inland.
The species is classed by the International Union for Conservation of Nature (IUCN) as critically endangered in the north-east Atlantic ocean.
Daily Mail