We found a growing regular presence of bottlenose dolphins along this stretch of Aberdeenshire coastline, south of Rattray Head

Karen Stockin, marine biologist

Marine biologist Karen Stockin, who led the study, said: "As the number of bottlenose dolphins appeared to decline off the Aberdeenshire coast, we then found a seasonal presence of white-beaked dolphins, presumed to be from offshore waters, from about July to September.

"It's not clear what is driving this relationship. It may be competition over prey."

Aberdeen University has secured funding for a PhD student to continue the research for three more years - and this relationship is expected to be one of the areas which will be examined further.

The 130 dolphins in the Moray Firth are the only such group resident around Europe's North Sea coasts - but the population is on the decline.

There are proposals to establish a Special Area of Conservation (SAC) which would cover the inner part of the Moray Firth.

Growing presence

However, Ms Stockin said her findings could have implications for the effectiveness of such a proposal.

The survey looked at an area from Fraserburgh to St Cyrus, near Montrose, focusing on a 12-mile stretch around Aberdeen Harbour and the coastline immediately south.

"We found a growing regular presence of bottlenose dolphins along this stretch of Aberdeenshire coastline, south of Rattray Head," she said.

There are 130 dolphins in the Moray Firth colony

"We've identified a peak period, during spring and early summer, where groups of up to 60 have been observed - but significantly there is a presence in these waters all year round.

"The SAC is a very important first step, but I think people now need to start addressing how effective that, on its own, is going to be if we are observing these dolphins expanding their home range for prolonged periods of time."

Ms Stockin said bottlenose dolphins were first reported off Aberdeen in the early 1990s.

However, the study suggested that a large group of the dolphins had expended their home range.

The study found nine species of whale and dolphin along the Aberdeenshire coastline, including the minke whale, harbour porpoises and white-beaked dolphins.

The UK's other main resident dolphin populations are in Cardigan Bay, Wales, and a grouping which has recently been identified off a large stretch of the south coast of England.