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INFORMATION AND CHARACTERISTICS.
The Atlantic white-sided dolphin is one of the six species of the genus Lagenorhynhus, which is well known to fishers and whalers of the North Atlantic ocean for many years. The word acutus in Latin means “sharpened,” a term referring to their sharp dorsal fin.
HOW DO THEY LOOK? PHYSICAL CHARACTERISTICS.
The Atlantic white-sided dolphin has a sturdy body with a thick, but very short snout and a wide tail. It has a curved and sickle-shaped dorsal fin that can reach up to 50 centimeters of height in the largest individuals. The long pectoral flippers protrude in the lower part of their body with a length of 30 cm. It has 30 to 40 pairs of pointed teeth in each row.
Weight and size.
Females are significantly smaller than males. The latter can reach a length up to 3 meters, but their average length is between 2.5 and 2.8 meters. Females reach up to 2.7 meters, although their average length is between 1.9 and 2.5 meters. The weight of both genders is between 200-230 kilograms.
This dolphin is one of the most colorful cetaceans alive. The Atlantic white-sided dolphin has a complex color pattern on its skin, characterized by featuring a black color on the dorsal area, both fins, and the flippers, and white color in the ventral and genital regions and part of the sides. It has a section of light gray skin from the eyes to the base of the tail and an ochre patch on both sides, over the black part of the dorsal area but near the tail. From the snout to the eyes it also has the dark color that extends in the form of a mask, but only in the upper jaw, as the lower jaw has the same light gray color than the ventral region.
The main feature to distinguish this species from others is its coloring pattern and, in particular, the ochre patch on both sides near the tail.
WHERE DO THEY LIVE? DISTRIBUTION AND HABITAT.
This dolphin is native to the North Atlantic Ocean, and its distribution only comprises the subpolar waters. Its habitat range starts from the region of New England (United States) in the west to France in the east reaching the north Greenland, Iceland, the British islands and all the Scandinavian peninsula. This species is common in the waters around the Hebridean islands, in the North Sea and the northern Islands of the Baltic Sea.
It inhabits open, temperate and cold waters of the platform and the continental slope in waters that have about 40-270 meters deep and temperatures of 6° to 20° Celsius. Also, it prefers habitats of low salinity.
WHAT DO THEY EAT? DIET AND EATING HABITS.
The Atlantic white-sided dolphin bases its diet on several species of fish and cephalopods as well as some species of crustaceans. In fact, their diet has variations because it depends on the geographic region where this cetacean dwell and the season of the year.
It shows a cooperative behavior to catch prey more efficiently and look for large schools of fish. It also associates occasionally with Fin whales (Balaenoptera physalus), Long-finned pilot whales (Globicephala melas) and humpback whales (Megaptera novaeangliae). But this dolphin does not hesitate to separate from its group if it has to feed more efficiently.
Their most common prey:
– Silver hake (Merluccius bilinearis).
– Atlantic mackerel (Scomber scombrus).
– Atlantic herring (Clupea harengus).
– Silvery pout (Gadiculus argenteus).
– Blue whiting (Micromesistius poutassou).
– Northern shortfin squid (Illex iilecebrosus).
HOW DO THEY REPRODUCE? MATING AND REPRODUCTION.
The reproduction of this species is similar to that of other dolphins, with differences in the gestation period and the age of sexual maturity. The female reaches maturity between 6 and 12 years of age at an approximate length of 1.94-2.22 meters. For its part, the male reaches maturity between 7 and 11 years or 2.1-2.4 meters in length.
The details of courtship and mating are still unknown. The female gives birth to one offspring of 1.1 meters long approximately every two years, from May to August or from June to July after a gestation period of 10-11 months. The mother breastfeeds the calf for about 12-18 months.
HOW DO THEY BEHAVE? BEHAVIOR.
Lagenorhynchus acutus is a gregarious, sociable and playful species. It groups in pods of 30 to 50 individuals that can join with other groups to make superpods of 500 and up to a few thousand dolphins. In some remote parts of Canada, the groups are smaller, composed of 6-8 dolphins. This species can associate with bottlenose dolphins (Tursiops truncatus), and fin and humpback whales. In the North Sea associations of Atlantic white-sided dolphins with white-beaked dolphins (Lagenorhynchus albirostris) are sometimes formed.
In each pod, there may be division according to age and sex. One hypothesis indicates that smaller groups are formed to facilitate feeding tasks while large groups are created to travel. In fact, some believe that this dolphin performs seasonal movements heading south in the winter and north in the summer within its distribution range.
The Atlantic white-sided dolphins enjoy performing acrobatic jumps and frequently ride the bow waves of boats and splash their tails on the surface of the water.
WHAT IS THEIR CONSERVATION STATUS? THREATS AND CONSERVATION.
Conservation status: Least Concern (LC).
In earlier times the species was hunted in Norway, and at present, this happens in Canada, the Faroe Islands, and Greenland. For this reason, direct hunting is an important threat to the survival of this dolphin, although fortunately it still has large populations.
The primary threats to this species are:
– Direct hunting.
– Bycatch in fishing nets.
– Pollution of their habitat with chemicals.
– Climate change and its repercussions on the ocean conditions.
– Massive dolphin stranding.
The conservation status of this species on the Red List of the International Union for Conservation of Nature (IUCN) is “Least Concern.” In 2006, the National Marine Fisheries Service (NMFS) implemented the Atlantic Trawl Gear Take Reduction Team to reduce bycatch of several cetacean species, including the Atlantic white-sided dolphin.
William F. Perrin, Bernd Würsig, J.G.M. ‘Hans’ Thewissen. Encyclopedia of Marine Mammals. Academic Press, 2009.