Scientists predicts cetaceans from as far away as the Pacific will live here as climate change heats up our waters

The waters around the British Isles could soon be home to several new species of mammals as a rising number of foreign visitors are being reported around our coasts. Experts believe the rare sightings of cetaceans from tropical climes could mean sea creatures are scouting for new territories to settle as global warming takes effect on sea temperatures.

Animals from the tropics, including the dwarf sperm whale, the pygmy sperm whale, and the Fraser's dolphin have all made recent appearances here, and the Cuvier's beaked whale, another warm-water species, has been recorded increasingly regularly in the west of Britain. The melon-headed whale, a squid-loving relative of the killer whale, has been seen in the Channel, off the coast of Brittany. Before too long we may see giants such as the 16-metre grey whale nudging into deep water around Cornwall and into the Irish Sea.

"We are now seeing a number of species far from home, and they probably will continue to recur with increasing frequency," said Peter Evans, director of the Sea Watch Foundation. "Several are normally found off west Africa. For the moment they tend to be seen at times of year when our sea temperatures are at their warmest. Whales and dolphins can cope with a wide range of temperatures but their fish and squid prey tend to be more constrained, and their ranges are extending significantly northwards."

He said cetaceans would follow their favourite food, and many species rare in colder waters just a decade ago had moved into British seas. This autumn a dwarf sperm whale was spotted in Mounts Bay, Cornwall, while a pygmy sperm whale, its close relative, was found beached on Seil island, near Oban.

"They were both very big surprises: they are rarely seen even where the populations are known to exist," said Evans. "If the fish are extending their range, as we know many are, then the whales and dolphins will follow. Anchovies, for example, were really quite scarce in the North Sea 10-20 years ago. Now they are widespread and may be why the common dolphin is now a regular in the North Sea.

"The behaviour of different fish, if they shoal or don't shoal, for example, requires a fair bit of understanding, so once a species has learned a feeding strategy they will follow rather than learn a new technique for a new prey."

Evans believes we may soon see a visitor that disappeared from the Atlantic in the 17th century – the grey whale. "They migrate up the west coast of north America, from Mexico and California up to the Arctic and, of course, could go no further. But now the Northwest Passage is open it is very possible they may cross the North Atlantic.

"A grey whale was seen last year off the coast of Israel and off Barcelona this year. Such a remarkable appearance in such a strange location reinforces the pattern we are seeing."

Twenty-nine species of dolphin and whale have been recorded this century in British or Irish territorial waters. The common dolphin, striped dolphin, minke whale and humpback whale are among those species where numbers sighted have increased since 1980.

But it is not just the whales moving north into warmer seas; we are also seeing mammals coming down from colder climes. Bearded seals from the Arctic have been seen off the coast of Fife, east Scotland, said Callan Duck, a senior research scientist at the Scottish Oceans Institute at St Andrews University.

"The change in climate and the food chains is definitely having an impact in the species we are seeing, but I think you have to remember to factor in how much better we are at spotting and recording these mammals. Good digital cameras are really accessible now, and so everybody has the opportunity to identify what they have seen – so the whole process of reporting sightings is much more accurate and efficient."