| Atlantic white-sided dolphin | |
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| Size compared to an average human | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Delphinidae |
| Genus: | Leucopleurus Gray, 1866 |
| Species: | L. acutus |
| Binomial name | |
| Leucopleurus acutus (Gray, 1828) | |
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| Atlantic white-sided dolphin range | |
TheAtlantic white-sided dolphin (Leucopleurus acutus) is a distinctively coloureddolphin found in the cool to temperate waters of the NorthAtlantic Ocean.
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),[3] weighing between 180–230 kg (400- 510 lb) once fully grown.[3] Females reach sexual maturity between the ages of 6 and 12 years, and males between 7 and 11 years old.[4][5] The gestation period is 11 months and lactation lasts for about 18 months — both typical figures for dolphins.[3] Atlantic white-sided dolphins are known to live for at least 17 years.[3]
The key distinguishing feature is the dolphin's coloration—a white to pale-yellow patch is found behind the dorsal fin on both sides of the body.[3] The white-sided dolphin's color variations are unique amongst the standard hues of white, grey, black and blue seen on other pelagic cetaceans.[3] Their body's coloration is well-demarcated, with the chin, throat and belly being white; the flippers,dorsal fin and back are dark-grey to black (with the exception of the yellow patch), and there is a further white patch below the dorsal fin (lying above a lighter, grayish stripe running from the beak, above the eye, down to the tail stock).[3]
Dolphin pod sizes vary by location, with groups averaging 60 in number having been seen close to theNewfoundland coastline, but somewhat smaller east ofIceland.[3] From the analysis of thestomach contents of stranded animals, fishes, such asherring andmackerel, andsquid appear to be the species' main prey.[3] The Atlantic white-sided dolphin is fairly acrobatic, and keen to interact with boats; however, it is not as wildly gregarious as thewhite-beaked,bottlenose orcommon dolphins.[3]
The species is endemic to the northern Atlantic Ocean.[3] The distribution limits are theNorwegian Sea in the northeast, theDavis Strait in the northwest, coastalNorth Carolina in the southwest and theCeltic Sea in the southeast (with possible range extension south to theAzores).[3] Areas of particularly high population density include the shores of Newfoundland andCape Cod, the triangular area of sea between theUnited Kingdom,Iceland andGreenland and the northernNorth Sea.[6][7][8] In 2008, sightings of Atlantic white-sided dolphins, as well as themelon-headed whale, were documented offSouth Carolina after a few strandings had taken place in the area at the time.[9] Along the North American east coast the species tends to occur in continental shelf waters, around 100m in depth,[10] and seem to show a preference toward areas of steep slopes and canyons.[11][12] They are associated with the colder, slightly less saline waters in the northern Atlantic, compared to for example common dolphins that are found in warmer, slightly more saline waters of the North Atlantic, though it is unclear whether this is due to preferences or if these factors influence prey supply.[13][14]
The diet of Atlantic white-sided dolphins mainly consists of herring,hake and squid.[3] However, as opportunistic carnivores, they consume a large variety of prey, including smaller mackerel and various bottom-dwelling fish.[3] They have been observed cooperatively hunting at the surface.[3] It has been suggested that larger groups split while feeding.[11]
Like all species of the dolphin family, Atlantic white-sided dolphins are very social animals, often traveling in large pods and displaying aerial behaviors as they travel.[15] The pod's size can vary, from several dozen to several hundred individuals, though the average size is around 50.[16] However, studies have shown there to be little familial relation between members of a group, appearing more as a social pod traveling for "safety in numbers". Researchers in different parts of their range have found that individuals were, mostly, unrelated to one another.[17][18] Juveniles spend at least some time in separate social groups, away from their parents, prior to weaning.[3] Atlantic white-sided dolphins jump and breach more frequently when in larger groups, as this behaviour might have a social context.[15] They have a wide vocal repertoire which includes squeals, whistles, clicks and buzzes.[16][19] It is suggested that vocalisation is used for communication as noise production increases during socialising.[19]
Despite being docile creatures, even known to interact with various species of cetacean in a nonviolent manner, most notably with thelong-finned pilot whale (Globicephala melas),[20] they have also been known to display violent behavior towardsharbor porpoises, attacking them until they eventually succumb to their wounds (a similar behavior as observed inbottlenose dolphins).[21][22]
Atlantic white-sided dolphins do not undertake specific seasonal migration.[11] However, they do move within their home range following prey distribution.[11] For example, in the waters off eastern North America this species moves southwards in winter and spring.[3][7]
Most of the calves are born around June and July.[3] The gestation period is 11 months and lactation around 18 months.[3] The birth interval varies between 1–3 years.[10]
Females reach sexual maturity around the age of 6–12 years.[4] Males reach sexual maturity around 7–11 years.[5] The reproduction is most likely seasonal, beginning in February, as some studies have identified dormant testes in some males.[5]
The Atlantic white-sided dolphin was named byJohn Edward Gray in 1828. The specific nameacutus comes from theLatin for 'pointed' and refers to the sharply pointeddorsal fin.[3] It was traditionally placed in the genusLagenorhynchus, but there was consistent molecular evidence that supports the Atlantic white-sided dolphin and thewhite-beaked dolphin asbasal members of the familyDelphinidae and not closely related.[23][24] In 2025 the Atlantic white-sided dolphin was therefore moved to its own genus,Leucopleurus.[25][26]
The estimations for the U.S. shelf and shelf-edge water suggest that the population size is about 300,000.[3] Additional 120,000 individuals have been estimated to spend summer in the Gulf of St.Lawrence.[3] In the eastern North America waters the numbers increase southwards in winter and spring in association with cold waters from the Gulf of Maine.[3] 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.
Historically, Atlantic white-sided dolphins were killed in drives conducted from Norway and Newfoundland.[27] These have ceased in recent years, although they still occur to a lesser extent from theFaroe Islands, where the meat and blubber are in high regard as food.[28] Reported catches in the years vary, though individual years suddenly stand out, such as in 2002, where the number reported killed was 773,[29] and in 2017, when 488 were killed.[28] In September 2021, a large pod of 1,428 animals was herded in Skálafjördur and killed.[30]
| Year | No/yr | drive/yr | Year | No/yr | drive/yr | Year | No/yr | drive/yr | ||
|---|---|---|---|---|---|---|---|---|---|---|
| 1980 | 8 | 1 | 1993 | 377 | 6 | 2001 | 546 | 7 | ||
| 1983 | 10 | 1 | 1994 | 263 | 7 | 2002 | 773 | 10 | ||
| 1985 | 32 | 1 | 1995 | 157 | 4 | 2003 | 186 | 5 | ||
| 1986 | 185 | 4 | 1996 | 357 | 7 | 2004 | 333 | 5 | ||
| 1987 | 76 | 2 | 1997 | 350 | 10 | 2005 | 312 | 4 | ||
| 1988 | 603 | 4 | 1998 | 438 | 4 | 2006 | 622 | 8 | ||
| 1990 | 55 | 2 | 1998 | 438 | 4 | 2008 | 1 | 1 | ||
| 1992 | 47 | 3 | 2000 | 265 | 3 | 2009 | 171 | 5 |
Atlantic white-sided dolphins have also been killed in incidental catch situations in the fishing industry. Such occurrences have been reported in Canada, United States, United Kingdom and Ireland.[1] Between 1977 and 1988, 13 Atlantic white-sided dolphins were reported as being incidentally caught in the Northeastern United States by U.S fisheries observers, 11 of these in Mackerel fisheries.[31] They have also been reported to get caught in pelagic or near surface trawl or drift nets.[11][16]
Anthropogenic underwater noise is a potential disturbance to Atlantic white-sided dolphins as they use sounds to communicate and catch prey.[19] A survey done in the UK showed that the sighting rate of Atlantic white-sided dolphins declines when airguns were firing compared to when they were not.[19]
Persistent organic pollutants (POPs) such as PCBs and organochlorine pesticides (e.g. DDT, DDE) and polybrominated diphenyl ether (PBDE) flame retardants have been identified in body tissues of Atlantic white-sided dolphins throughout their range.[6][32][33][34] Males had higher levels of PCBs suggesting that females pass some of the contamination to offspring during lactation[30]. Similarly to other species, studies have identified heavy metals in Atlantic white-sided dolphins including cadmium levels higher than in other dolphin species in southern latitudes.[35] The full effect of this contamination is currently unknown.
The International Union of the Conservation of Nature (IUCN) currently classifies Atlantic white-sided dolphins asLeast Concern.[1]
The North and Baltic Sea populations of the Atlantic white-sided dolphin are listed on Appendix II[36] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). They are listed on Appendix II[36] as they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.[37] These species of dolphin are known to fall victims to in a polluted environment, a study from 1997 confirmed that the British and Irish populations of Atlantic white-sided dolphins to succumb to these effects.[6][38][clarification needed]
In addition, the Atlantic white-sided dolphin is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS).[39]
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