Bottlenose dolphin Tursiops truncatus around the UK are considerably larger than individuals of the same species in most parts of the world, reaching up to around 4 m in length, although 2.5-2.7 m is a more usual adult length. It is primarily an inshore species, with most sightings within 10 km of land, but they can also occur offshore, often in association with other cetaceans.
Most offshore animals probably represent a separate population, although some inshore dolphins may move offshore during the winter months. Large aggregations of many hundreds of individuals have been recorded off the Atlantic coast of Ireland, but typically single animals or small groups of up to 25 animals are sighted. A small number of semi-resident inshore populations are known.