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Lagenorhynchus acutusAtlantic white-sided dolphin

By Holly Kopack

Geographic Range

The distribution of the Atlantic white-sided dolphin is the cool temperate and subartic waters of the north Atlantic Ocean from southern Greenland to Massachusetts, and from the British Isles to western Norway. It has also been reported as far as the sourthern Barents Sea, the Baltic Sea, the Azores, and the Adriatic Sea.

Habitat

Lagenorhynchus acutus is typically found in cool pelagic waters, where its major predators are killer whales and sharks. Since it usually prefers the open water, L. acutus is not commonly seen from shore. It mostly occupies waters of 40 to 270 m in depth around the continental shelf. L. acutus seems to prefer a surface temperature between 6 to 20 degrees Celsius and areas with low salinity.

Physical Description

Lagenorhynchus acutus ranges from 2.5 to 3 meters in length. The pectoral fin is about 30 cm in length and the dorsal fin may be up to 50 cm in height. The tail flukes range from 30 to 60 cm across. Females may be considerably smaller than males and average only 182 kg.

The dorsal region of L. acutus is black, while its sides are gray. The ventral regions are white from the lower jaw to just past the anus. Within the gray sides are yellowish white patches, which are probably its most distinct characteristic (Minasian et al., 1984). Black rings around the eyes are also present. The dorsal fin is tall, sharply curved and pointed at the tip, giving the species the name acutus or, Latin for "sharp". Lagenorhynchus acutus has a stocky body with sickle shaped fins and a thick tail stock. The beak is prominent with 30 to 40 pairs of pointed teeth. (Minasian, et al., 1984)

  • Sexual Dimorphism
  • male larger
  • Range mass
    180 to 250 kg
    396.48 to 550.66 lb

Reproduction

Information on the mating system of these animals is not available.

The gestation period is about 10 months long. The calves are usually born in June and July. There is usually one young per a birth, averaging about 25 kg and 107 to 122 cm in size when born. The young are usually weaned at 18 months. The calving interval is 2 to 3 years.

Males become sexually mature between 2.1 and 2.4 m in length. Females become sexually mature between 1.94 and 2.22 m in length, which probably corresponds to 12 years of age (Klinowska, 1991). The maximum longevity of males is probably 22 years, whereas female longevity is 27 years. (Klinowska, 1991)

  • Breeding interval
    The calving interval is 2 to 3 years.
  • Average number of offspring
    1
  • Average number of offspring
    1.25
    AnAge
  • Average gestation period
    10 months
  • Average gestation period
    316 days
    AnAge
  • Average weaning age
    18 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    2231 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    12 years

Lifespan/Longevity

Behavior

Lagenorhynchus acutus is a gregarious species and may be found in groups of up to 1,000 individuals. However, groups of only 6 to 8 individuals are more common off of Canada and in other places along the western Atlantic. Inshore herds are also small, ranging from about 10 to 60 animals. It seems that immature animals and newly mature males are absent from larger breeding groups, which may indicate some form of segregation among the herds (Atlantic white-sided dolphin, 1999).

Lagenorhynchus acutus typically dives for less than five minutes. These animals are sometimes seen riding the bow waves of larger species.

Mass strandings of L. acutus are common on northern Altantic shores. The strandings sometimes occur in groups of 3 to 15 or more animals, although they usaully occur in pairs (National Marine Life Center, 1999). The last major stranding of L. acutus occured on Cape Cod in 1995, when approximately 30 animals were beached on the shore (Dolphin Death Toll Tops 70 on Cape Cod, 1998). Lagenorhynchus acutus does not usually survive strandings (Knapp, 1999).

Lagenorhynchus acutus appears to be very nomadic but, there are no data showing a set of seasonal migrations. The distribution patterns may correspond to abundance of important prey species (Klinowska, 1991). (Klinowska, 1991)

Communication and Perception

Food Habits

The prey of L. acutus is usually a combination of shrimp, smelt, hake, squid and herring. These animals may separate from their school in order to feed more efficiently.

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Economic Importance for Humans: Positive

Occasionally, L. acutus is captured deliberately by fisherman off Newfoundland, Norway, and the British Isles, presumably to be sold in fresh meat markets (Nowak, 1999). Historically, L. acutus has also been hunted by Greenland. The Faeroe Islands take hundreds of L. acutus every year, by driving large schools ashore (CETACEA: Lagenorhynchus acutus, 1999). Unlike many other dolphin species, L. acutus has not been reported to be in captivity (Atlantic white-sided dolphin, 1999).

Economic Importance for Humans: Negative

A small number are caught in fishing nets each year, causing damage to fishing productivity.

Conservation Status

Data on the population size of L. acutus is scarce but, the species is usually considered regionally abundant. The main threats today come from pollutants and entanglement in fishing gear (Whale and Dolphin Species Information, Humpback Whale and others, 1999).

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Holly Kopack (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

piscivore

an animal that mainly eats fish

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

"CETACEA: Lagenorhynchus acutus (Atlantic White-Sided Dolphin)" (On-line). Accessed December 28, 2004 at http://www.cetacea.org/aside.htm.

Klinowska, M. 1991. Dolphins, Porpoises and Whales of the World. Gland, Switzerland and Cambridge, U. K.: IUCN.

Minasian, S., K. Balcomb, L. Foster. 1984. The World's Whales. Washington, D. C.: Smithsonian Books.

Nowak, R. 1999. Walker's Mammals of the World 6th Edition. Baltimore and London: The Johns Hopkins University Press.

Parker, S. Grzimek's Encyclopedia of Mammals. New York, St. Louis and San Francisco: McGraw-Hill Publishing Company.

Reeves, R., S. Leatherwood. 1994. Dolphins, Porpoises, and Whales. Gland, Switzerland: IUCN.

van der Toorn, J. 1999. "Atlantic white-sided dolphin" (On-line). Accessed December 28, 2004 at http://ourworld.compuserve.com/homepages/jaap/.

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