Atlantic White-Sided Dolphin

The Atlantic white-sided dolphin is a relatively small dolphin. At birth, calves measure just over a meter long; adult males grow to about 2.8 m (9.2 ft), and females to about 2.5 m (8.2 ft), weighing between 180 and 230 kg (400- 510 lb) once fully grown. Females reach sexual maturity between the ages of 6 and 12 years, and males between 7 and 11 years old. The gestation period is 11 months and lactation lasts for about 18 months — both typical figures for dolphins. Atlantic white-sided dolphins are known to live for at least 17 years.

The species is endemic to the northern Atlantic Ocean. The distribution limits are the Norwegian Sea in the northeast, the Davis Strait in the northwest, coastal North Carolina in the southwest and the Celtic Sea in the southeast (with possible range extension south to the Azores). Areas of particularly high population density include the shores of Newfoundland and Cape Cod, the triangular area of sea between the United Kingdom, Iceland and Greenland and the northern North Sea. In 2008, sightings of Atlantic white-sided dolphins, as well as the melon-headed whale, were documented off South Carolina after a few strandings had taken place in the area at the time. Along the North American east coast the species tends to occur in continental shelf waters, around 100m in depth, and seem to show a preference toward areas of steep slopes and canyons.

The diet of Atlantic white-sided dolphins mainly consists of herring, hake and squid. However, as opportunistic carnivores, they consume a large variety of prey, including smaller mackerel and various bottom-dwelling fish. They have been observed cooperatively hunting at the surface. It has been suggested that larger groups split while feeding.

Most of the calves are born around June and July. The gestation period is 11 months and lactation around 18 months. The birth interval varies between 1–3 years.

Females reach sexual maturity around the age of 6–12 years. Males reach sexual maturity around 7–11 years. The reproduction is most likely seasonal, beginning in February, as some studies have identified dormant testes in some males.

The estimations for the U.S. shelf and shelf-edge water suggest that the population size is about 300,000. Additional 120,000 individuals have been estimated to spend summer in the Gulf of St.Lawrence. In the eastern North America waters the numbers increase southwards in winter and spring in association with cold waters from the Gulf of Maine. Two projects attempted to estimate the population trends - multinational Small Cetacean Abundance in the North Sea and Adjacent Waters (SCANS) survey project and the North Atlantic Sightings Survey (NASS). SCANS surveys, however, failed to produce species specific estimation as it combined both white-sided and white-beaked dolphins. NASS surveys did not indicate any population trends.