Atlantic White-Sided Dolphin
Collaborating author : Nicole Vollmer, Smithsonian – VollmerN@si.edu
Species: Lagenorhynchus acutus
Length: males up to 2.8 m, females up to about 2.5 m (1)
Weight: 180-234 kg (2, 3)
Life expectancy: estimated maximum age for males is 22 years and females is 27 years (2)
Atlantic white-sided dolphins jumping off the coast of anticosti
Description and Taxonomy: Atlantic white-sided dolphins are toothed whales, or odontocetes. They are most easily identified by the sharply defined, narrow white patch that runs along their flanks beginning below the dorsal fin. The white patch ends abruptly and is continued by a yellow-tan patch that runs towards the fluke, or tail. The dolphins' back, falcate dorsal fin, flippers, and top beak are black and their lower beak and ventral sides are white. Atlantic white-sided dolphins, like most odontocetes, have rows of sharp, conical teeth along their upper and lower jaws, which they use to catch their prey. The Atlantic white-sided dolphin is currently one of six species grouped together within the genus Lagenorhynchus; however, data based on molecular genetics suggests that the six members of this genus are not closely related and should be split up into multiple different genera (e.g., 4, 5). At the population level, there is currently no evidence to support that the Gulf of St. Lawrence harbors a resident, genetically distinct population of Atlantic white-sided dolphins, and molecular and morphological studies are ongoing to investigate population structure of this species across the North Atlantic (6-8).
Distribution: The Atlantic white-sided dolphin is found in temperate and sub-polar waters across the northern Atlantic Ocean, in the east ranging typically from the Brittany coast of France, north to Norway and Iceland, southern Greenland, and in the western North Atlantic down to just south of Cape Cod, Massachusetts (9). These dolphins typically inhabit oceanic waters along the continental shelf and slope and are considered to be relatively abundant across their range. Within the Gulf of St. Lawrence, the Atlantic white-sided dolphin is most commonly observed at the mouth during summer months and more frequently sighted within the Gulf in August and September, although since the late 1990's, sightings within the Gulf have generally decreased (*).
Life History: Females reach sexual maturity around 6-12 years of age, typically around 2.1 m in length, while males are sexually mature around 7-11 years and around 2.3 m in length. Gestation is estimated to last on average 11 months with calves most commonly sited from May to September, and females give birth to one calf every 1-2 years (2, 3, 10, 11).
Diet: Atlantic white-sided dolphins are known to feed predominantly on fish from a variety of species including silver hake, haddock, pelagic Atlantic herring, mackerel, silvery pout, whiting, and lantern fishes, and also on some invertebrates including common squid and octopus (2, 12-14). There is some evidence that the favored prey type changes geographically and seasonally (3).
Behavior: The Atlantic white-sided dolphin is a gregarious and highly social species that lives and travels in groups of 5 to 500 individuals. The mean group size typically varies depending on location. There has been some evidence suggesting that these dolphins travel in groups that are segregated based on sex and/or age (2, 15). Also, mass strandings of Atlantic white-sided dolphins, of up to 100 or more individuals, is not uncommon, particularly in the western North Atlantic, although the causes of these strandings are unknown (16). As odontocetes, Atlantic white-sideds and other dolphins have the ability to use echolocation to find their prey in deep, murky waters. The dolphin emits clicks produced in their sinus cavities and directs them out into the water column through their melon, or forehead, where the sound waves bounce off objects and allow the dolphin to acoustically visualize where its prey is and what kind of fish or invertebrate it is.
Conservation: According to the International Union for Conservation of Nature and Natural Resources (IUCN), the Atlantic white-sided dolphin is considered Least Concern (9). However, threats from bycatch are of particular concern, as members of this species are vulnerable to entanglement in commercial fishing gear and have been incidentally killed in trawl nets throughout the North Atlantic (3, 16).
(1) Perrin WF, Reilly SB. 1984. Reproductive parameters of dolphins and small whales of the Family Delphinidae. Rep Int Whal Commn Special Issue 6: 97-133.
(2) Seargent DE, St. Aubin DJ, Geraci JR. 1980. Life history and Northwest Atlantic status of the Atlantic white-sided dolphin, Lagenorhynchus acutus. Cetology 37: 1-12.
(3) Cipriano F. 2009. "Atlantic white-sided dolphin, Lagenorhynchus acutus." Encyclopedia of Marine Mammals. 2nd Ed. Perrin WF, Würsig B, Thewissen JGM, eds. Boston: Academic Press. 56-58.
(4) LeDuc RG, Perrin WF, Dizon AE. 1999. Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Mar Mamm Sci 15: 619-648.
(5) McGowen MR. 2011. Toward the resolution of an explosive radiation - a multilocus phylogeny of oceanic dolphins (Delphinidae). Mol Phylogenet Evol 60: 345-357.
(6) Vollmer NL, Gonzalez V, Lesage V, Potter C, Rosel P, Wenzel F. 2015. Detection of fine-scale population structure of the Atlantic white-sided dolphin (Lagenorhynchus acutus) in the western North Atlantic using RAD-seq data. 21st Biennial Conference on the Biology of Marine Mammals, San Francisco, CA.
(7) Banguera-Hinestroza E, Evans PGH, Mirimin L, Reid RJ, Mikkelsen B, Couperus AS, Deaville R, Rogan E, Hoelzel AR. 2014. Phylogeography and population dynamics of the white-sided dolphin (Lagenorhynchus acutus) in the North Atlantic. Conserv Genet 15: 789-802.
(8) Fernández R, Schubert M, Vargas-Velázquez AM, Brownlow A, Víkingsson GA, Siebert U, Jensen LF, Øien N, Wall D, Rogan E, Mikkelsen B, Dabin W, Alfarhan AH, Alquraishi SA, Al-Rasheid KA, Guillot G, Orlando L. 2016. A genomewide catalogue of single nucleotide polymorphisms in white-beaked and Atlantic white-sided dolphins. Mol Ecol Resour 16: 266-276.
(9) Hammond PS, Bearzi G, Bjørge A, Forney K, Karczmarski L, Kasuya T, Perrin WF, Scott MD, Wang JY, Wells RS & Wilson B. 2008. Lagenorhynchus acutus. The IUCN Red List of Threatened Species 2008: e.T11141A3255721. http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T11141A3255721.en. Downloaded on 26 February 2016.
(10) Weinrich MT, Belt CR, Morin D. 2001. Behavior and ecology of the Atlantic white-side dolphin (Lagenorhynchus acutus) in coastal New England waters. Mar Mamm Sci 17: 231-248.
(11) Rogan E, Baker JR, Jepson PD, Berrow S, Kiely O. 1997. A mass stranding of white-sided dolphins (Lagenorhynchus acutus) in Ireland: biological and pathological studies. J Zool Lond 242: 217-227.
(12) Craddock JE, Polloni PT, Hayward B, Wenzel F. 2009. Food habits of Atlantic white-sided dolphins (Lagenorhynchus acutus) off the coast of New England. Fish Bull 107: 384-394.
(13) Couperus AS. 1997. Interactions between Dutch midwater trawl and Atlantic white-sided dolphins (Lagenorhynchus acutus) southwest of Ireland. J Northw Atl Fish Sci 22: 209-218.
(14) Hernandez-Milian G, Begoña Santos M, Reid D, Rogan E. 2015. Insights into the diet of Atlantic white-sided dolphins (Lagenorhynchus acutus) in the Northeast Atlantic. Mar Mamm Sci. doi: 10.1111/mms.12272
(15) Amaral KA. 2005. Atlantic white-sided dolphin (Lagenorhynchus acutus) social structure based on stranding trends and genetics. Master's Thesis, University of Massachusetts, Dartmouth. Dartmouth, MA. 104pp.
(16) Waring GT, Josephson E, Maze-Foley K, Rosel PE, editors. 2015. US Atlantic and Gulf of Mexico marine mammal stock assessments – 2014. NOAA Tech Memo NMFS NE 231; 361 pp.
(*) unpublished data