Some of the short-beaked common dolphins which were seen in the Moray Firth
Hundreds of dolphins more commonly found in warmer seas have been seen in the Moray Firth while making a "massive migration" into the North Sea.
The environmental charity Earthwatch Institute said more than 400 short-beaked common dolphins were sighted off the north east coast.
It said the "super pod" was a sign of how climate change was pushing some wildlife further north.
The firth is famous for its bottlenose dolphins.
An Earthwatch team headed by Dr Kevin Robinson, director and co-founder of the Cetacean Research and Rescue Unit (CRRU), saw the pod 10 miles off land.
He said the dolphins' appearance in the firth was hugely significant.
Dr Robinson said: "Firstly, the sheer number of dolphins was astounding - there were common dolphin everywhere around us over a two-mile radius.
"Furthermore, this was only the second sighting in the past few years of such a 'super-pod' of this species in these waters. The first sighting in 10 years was recorded here in July 2007 when we were joined by more than 300 animals in the outer Moray Firth.
"Since then we have not seen them, although smaller groups have been identified by co-workers from the Whale and Dolphin Conservation Society on opportunistic boat surveys."
He said "super pods" were known to exist in other parts of the UK. There have been sightings in the Western Isles, but few in the firth.
The scientist added: "This is further scientific evidence that populations of dolphins are moving further north because of climate change."
Christina Gore, a 61-year-old Earthwatch volunteer who was also on the boat trip, said the water was "boiling with animals".
She said: "It was incredibly exciting. They were swimming under the boat and leaping alongside us. There were older animals doing back-flips, and there were even newborn calves swimming along with the group."
Charlie Phillips, of the WDCS, said common dolphins could be seen in the Inner Moray Firth where the stretch of water narrows in the summer.
He said the numbers in the group seen by Dr Robinson off Fraserburgh were amazing.
Mr Phillips said: "To see wall-to-wall dolphins is something to behold."
Large sand eel and mackerel shoals off the Caithness coast may see the "super pod" move into the Pentland Firth, he added.