Warmer seas could be responsible for a change in the type of dolphins spotted off the coast of the North East of England, a survey has suggested.
The North East Cetacean Project found an increase in sightings of common, bottlenose and Risso's dolphins - species associated with warmer waters.
There have also been fewer sightings of white-beaked dolphin and harbour porpoise, which prefer colder water.
It is thought the distribution shift is due to increasing sea temperatures.
The NECP is a partnership including the charity Marinelife, Northern Experience Wildlife Tours, Natural England, the Northumberland and Tyneside Bird Club and the University of Aberdeen.
Dr Tom Brereton, who analysed the findings, said: "This research adds to the growing body of evidence that some species of whales and dolphins are showing shifts in distribution, possibly as a result of increasing sea temperatures.
"For example, common dolphins have been spreading north in recent years, presumably due to warming sea temperatures.
"This is a potential cause of concern because studies in other regions have shown that the arrival of common dolphins coincides with a corresponding disappearance of white-beaked dolphins.
"White-beaked dolphins have a much narrower habitat requirement and are associated with colder sea conditions."
The project is asking the region's fishermen, recreational dive and angling boats, yachtsmen, and pleasure craft operators to get in touch with any offshore sightings.