Bottlenose dolphin

Habitat: Throughout British waters; offshore at shelf break and close inshore, including estuaries, harbours; may briefly come into fresh water. Favours areas with strong tidal currents and steep bottom relief.

Description: Robust, torpedo-shaped. Head is stout with blunt, bottle-shaped beak. Abrupt junction between upper jaw and beak. Dorsal fin is centrally placed, tall, usually sickle-shaped but can be triangular, particularly in young individuals. Flippers pointed. Tail stock moderately keeled, tail flukes with deep median notch. Colouration variable, generally counter-shaded; black, brown, or dark grey on back, lighter grey flanks, white or cream on belly. Calves are generally paler, often light grey, cream, or olive. Adults may have indistinct cape marking from melon to dorsal fin. Scars common, particularly around jaws. Patches of skin discolouration from disease common in British waters.

Size: Around 3.2 - 3.4 m; males larger. Populations in colder climates larger; animals around British Isles some of the largest in the world.

Weight: Up to 365 kg.

Lifespan: Males 40 - 45 years, females up to 50 years.

Distribution: Worldwide, coastal and offshore tropical and temperate waters. In NE Atlantic, locally common from N Africa to N Scotland. Variable site fidelity in coastal habitats. North Scotland is current northern limit of coastal range; offshore range at least to Faroes. Little known about ecology of offshore animals, although often associated with pilot whales.

Diet and feeding: Selective opportunist. Includes variety of benthic and pelagic, solitary and schooling, fish and cephalopods. Individuals may specialise on particular prey or switch as availability changes. Independent and cooperative feeding observed. Local topography, shore line, water surface, tidal interfaces used to herd prey. Exploits human fisheries in several parts of the world, particularly trawling and gillnets. Other than direct competition for prey and accidental capture in fishing nets, few interactions between human fisheries and bottlenose dolphins in British waters are known. Probably feeds by day and night. Captive individuals require 3 - 6 % of body weight in food per day. 

Breeding: Mating system unclear, but competition for access to females implied by violent interactions between males, heavy body scarring, formation of male-male alliances, and subtle size dimorphism. Mating systems may vary between populations. Extended season for births, peak May - November in British Waters. Gestation period 12 months, lactation period 18 - 20 months (suckling may last several years, weaning gradual), calving interval 2 - 5 years.

Conservation status and population: Listed by IUCN as data deficient. British inshore population at least 490 individuals. SCANS II survey in 2005 estimated 12,600 bottlenose dolphins in Western European continental shelf waters, mostly offshore. 

Diverse anthropogenic threats. Physical injury from boat strikes, explosions, entanglement in fishing gear occur. Toxins and contaminants have impact on immune and reproductive systems. Habitat alteration, overfishing reduce prey abundance. Noise disturbance may disrupt social communication and foraging.

Identification

Robust, with stout beak. Counter-shaded grey colouration with no contrasting colour patches. Can be confused with harbour porpoise and white-beaked dolphin; key features colouration, dorsal fin, demarcated melon. May be seen alone or in groups.

Vocalisations: Diverse. Echolocation clicks intense, short duration, broadband (40 - 130 kHz), culminate in buzzes and whines as approaching target. Burst pulse vocalisations - barks, yelps, brays - 0.2 - 16 kHz. Whistles, pure tone FM calls 2 - 20 kHz, produced in social contexts.