Fishermen in Cornwall say warmer waters are bringing with them species rarely seen around our coastline.
A new report says water temperature around the British coast is rising because of climate change and this is affecting marine life including the bluefin tuna.
Bluefin tuna were common in UK waters last century until the mackerel and herring they eat was overfished.
Since then there have been few sightings until recently when warm waters have brought back the fish they eat.
Dave Bond, a fisherman from Looe, recently took a trip out angling when a sixteen-year old enthusiast landed a blue fin tuna weighing 160 pounds.
"We were actually fishing for blue sharks so we were float fishing and we'd had two sharks and then we had another one thinking it was another shark. As the fight went on which, what, nearly an hour it took until when we finally got the plate up to the boat it actually was a bluefin tuna."
Mr Bond agrees with the report that the shift in water temperature is the reason the tuna have returned.
"The climate is getting warmer, the waters are warming up and we're finding more exotic species in these waters."
Fishermen in the UK are not allowed to land blue fin tuna because the country has no quota for the fish, but Mr Bond says that this won't stop keen anglers from chasing the returning giants.
"This year it's still a little bit early. Last year the shoals appeared in August and we're hoping it's going to be a repeat of that this year. If the shoals appear, several of the boats have geared up with heavier gear, hopefully to prosecute that fishery."
The report was published by the UK Marine Climate Change Impacts Partnership (MCCIP). It says that as well as tuna, squid and anchovies are returning to UK waters.