Atlantic White-Sided Dolphin – Leucopleurus acutus
Habitat: More pelagic than white-beaked dolphin. Occurs mainly along edges or seaward of continental shelves, over depths of 100 – 300 m. May come on to continental shelves, may enter fjords and inlets with depths < 50 m.
Description: Stout, torpedo-shaped body, rounded snout with short beak (around 5 cm). Back, tail, top of head, and upper jaw are black; flanks are grey with thin white patch extending from below dorsal fin about halfway to the tail, and yellow-ochre patch stretching above grey flank from mid point of dorsal fin down the tail stock. Black eyepatch connected to mouth and flipper insertion by thin black line. Black patch around genital/anal opening. Lower jaw and belly are white. Flippers pointed, strongly re-curved, black. Dorsal fin is relatively talkk, centrally placed, sickle-shaped. Tail stock isis high, parallel-sided, particularly in adult males, in which it sudenly narrows close to the slightly notched tail flukes. Flukes have concave trailing edge.
Size: 2.1 – 2.6 m, males larger (male maximum 2.7 m, female maximum 2.5 m)
Weight: male maximum 234 kg, female maximum 182 kg.
Lifespan: Assuming one dentine layer per year, oldest recorded female 27 years, oldest recorded male 22 years.
Distribution: Restricted to north North Atlantic, mainly offshore waters, from south west Greenland, Iceland, and west Barents Sea south to Virignia (USA) and the Bay of Biscay. Off British Isles, concentrated around Hebrides, N Isles, and nort North Sea, but extends south along Atlantic seaboard, mainly outside or near the continental shelf, west and south of Ireland and Bay of Biscay; rare in Irish Sea, English Channel, south North Sea.
Diet & Feeding: Wide variety of fish, squid, and shrimps. Small groups frequently seen herding fish by surface-rushing in crescent-shaped formation.
Breeding: Data limited. Births mainly in May – August, as early as February and as late as September. Gestation period 11 months; lactation period 18 months; calving interval 2 – 3 years and some individuals may be both lactating and pregnant. Age at sexual maturity probably 7 – 11 years for males and 6 – 12 years for females.
Conservation Status & Population: Listed by IUCN as lower risk / least concern. No comprehensive population estimates exist.
Not hunted commercially, although taken opportunistically by drive fisheries in Faroes, with up to 500 taken some years. Formerly hunted in Norway and Canada. Probably hunted in small numbers off south west Greenland. Incidental mortality in fishing gear reported from British Isles, Ireland, and Canada. Numerous in bycatches from former Dutch trawl fishery for mackerel and horse-mackerel near shelf edge west and south of Ireland; 90% of this mortality occured February and March.
Similar to white-beaked dolphin but smaller.
Vocalisations: Includes whistles of 7 – 16 kHz with mean peak frequencies of 8 – 12 kHz, mean duration 0.5 s. Broadband echolocation clicks at 0.2 – 180 kHz with peak frequencies 60 – 80 kHz and single pulse duration of 0.25 – 1 ms.