 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 m 