Tuna found dead in cold water shallows of Eyre Peninsula's Coffin Bay

Kane Slater who found the tuna with his kids Arj and Tallara says he has never seen a tuna that big in the area. (Supplied)

A two-and-half-metre tuna has been found washed up in the shallow waters of Yangie Bay, off Coffin Bay on the Eyre Peninsula, over the weekend.

Kane Slater was out fishing with his children when they spotted a fin sticking out of the water close to shore.

He initially estimated the fish found in Yangie Bay was around 90 kilograms in weight, however he later confirmed it would have been double that — weighing 180kg.

Mr Slater says he's unsure how long the dead tuna had been there for. (Supplied)

Mr Slater said they initially thought it was another sea creature.

"We saw this fin out of the water, laying close to the beach on the northern side, and the kids go 'look, there's a dead dolphin dad'," he said.

"We went over that way and got off the boat and … as we got closer we realised that it was a massive tuna."

A former fisheries officer, Mr Slater said it was uncommon to see a tuna in the bay at this time of year with the cool water temperatures.

"I haven't seen it that big," he said.

Mr Slater's children Arj and Tallara spotted the fin of the fish in the water. (Supplied)

Mr Slater said tuna of this size were not usually seen in the area until the warmer months.

He said recent high tides and wild weather could have contributed to the fish being caught in the bay.

The tuna was found in Yangie Bay, off Coffin Bay, in South Australia. (Supplied)

"When those big fronts come through in winter, you do see some species of animals that aren't common around here," he said.

"Sometimes the adverse weather in the winter can push up these species that you don't usually see.

Mr Slater says he's spoken to locals who say there's been less than a handful of tuna this size found in the area in winter. (Supplied)