“This last week we have had some massive tides so it’s probably followed the salmon and everything else up the river,” he said.”You do not usually get tuna in British waters but as the water temperature increases, they are getting spotted more and more.”The water temperature in the River Severn is about 17C, which is really warm for this time of year. That means all the fish from the west coast of France, the Bay of Biscay for instance, come around the corner and into the Bristol Channel. A 7ft-long tuna fish has been found dead in the River Severn near Gloucester – hundreds of miles from its normal habitat in warm sea waters.Friends Kevin Brady, Steve Burgess and Alec Foster found the giant fish in the estuary at Minsterworth, Glos, at the weekend when they were paddle boarding.It had been washed up into the side of the river better known for salmon and elvers. Steve spotted it on his jet ski and came to myself and Alec on our paddle boards. He was shouting ‘I’ve found a 7ft fish!’ We didn’t believe him, thinking it must be a cow or somethingKevin Brady “Basically the big fish follow the smaller fish and climate change means they come in further.”Mr Francis said that in years gone by, North East ports were known for excellent tuna fishing and the rich would go there on their yachts to try and catch the species that are now more likely to be found in a can.And although the fish in the Severn looks like a whopper, it probably can’t compete with a 526lb tuna found off the coast of Scarborough.The World Wildlife Fund say if fish were cars, tuna would be the Ferraris of the ocean world as they are sleek, powerful, and made for speed.There are several species but the Atlantic bluefin can reach 10ft in length and weigh as much as 1500 pounds, more than a horse, and can swim up to 43 miles per hour across long distances.”Some tuna are born in the Gulf of Mexico, cross the entire Atlantic Ocean to feed off the coast of Europe, and then swim all the way back to the Gulf to breed,” the WWF says. Mr Brady, who last year became the first person ever to swim the full length of the 220-mile River Severn, showed off his catch of the day on social media.Mr Brady, 33, said: “Steve spotted it on his jet ski and came to myself and Alec on our paddle boards.”He was shouting ‘I’ve found a 7ft fish!’ We didn’t believe him, thinking it must be a cow or something.”Mr Brady added: “It wasn’t until we got right up next to it we realised it was a fish.”Dai Francis, of the Severn and Wye Smokery at Minsterworth, said he was not surprised to hear a tuna had come so far upriver. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.