Dolphins And Porpoises

Although the only true ice-associated cetaceans are the beluga (Delphinapterus leucas), the narwhal (Monodon monocerus), and the bowhead whale (Balaena mysticetus), there are several small cetaceans that also live in Arctic waters. The killer whale (Orcinus orca) can often be found near the ice edges off Iceland, Greenland, Alaska, and the Russian Far East (Kamchatka, Sakhalin, and the Okhotsk Peninsula), frequently north of 70° N latitude. In the North Atlantic, long-finned pilot whales (Globicephala melas) are sometimes found as far north as Iceland and Finnmark. Killer whales and pilot whales are delphinids; other dolphins that frequent Arctic or Subarctic waters are the white-beaked dolphin (Lagenorhynchus albirostris) and the Atlantic white-sided dolphin (Lagenorhynchus acutus). The harbor porpoise (Phocoena phocoena) and Dall's porpoise (Phocoenoides dalli) are the only Arctic pho-coenids.

The white-beaked dolphin is the largest of the "lags" (the common name for members of the genus Lagenorhychus), reaching a length of 10 ft (3 m). The dorsal fin is large, dark, and strongly recurved. As its name implies, it has a black head and a short white beak. In Norwegian this characteristic translates to hvidnaese, in Swedish it is vitnosdelfin, and in German it is known as Weisschnauzendelphin. It has grayish patches on the flanks and the dorsal surface of the tail stock, but it is not as crisply marked as the other North Atlantic lag, the white-sided dolphin, sometimes seen in groups of 1000 or more, but more commonly in schools of around 30-50. Like the other lags, it is acrobatic and fond of jumping. It is a frequent bow-rider, and seems to be attracted to small boats. It is sometimes known as "squidhound" in Newfoundland, but it also eats various fishes and benthic crustaceans. It is common in the northern and central North Sea, and in the Skagerrak between Jutland (Denmark) and Norway. The white-beaked dolphin has been described as common around the Faroe Islands, and they are also found in the waters of Greenland, Newfoundland, and Labrador, and occasionally as far south as Cape Cod.

Although the ranges of the two North Atlantic lags often overlap, they can be differentiated by the white beak of L. albirostris, and the yellow flash and the pronounced keels of the white-beaked dolphin. The Atlantic white-sided dolphin (Lagenorhynchus acutus) has a prominent yellowish or orange patch on the tail-stock that is often visible when the animal jumps. This species jumps so frequently that it is known as "jumper" by Newfoundland fishermen, and "springer" by Germans. In Icelandic it is leiftur, in Danish hvidskaeving, in Faroese hvitskjorutor springari, and in Russian belobokii del'fin. It has a robust body and a short, thick beak, and can reach a length of 9 ft and a weight of 510 lb (230 kg). This species is also characterized by greatly exaggerated "keels" on the dorsal and ventral aspects of the caudal peduncle. It is found only in the northern North Atlantic, but not as far north as the white-beaked dolphin. The white-sided dolphin often aggregates in large herds, sometimes numbering in the hundreds, but they are more commonly seen in smaller groups of 10-50 individuals. Their range is restricted to the temperate and Subarctic portions of the North Atlantic, and includes the waters of southern Greenland, Iceland, Spitsbergen, and Scandinavia. They appear seasonally off Newfoundland and the Gulf of St Lawrence, and may be year-round residents of the Gulf of Maine. The Faroese drive-hunt, usually directed toward pilot whales, also takes many white-sided dolphins, sometimes as many as 500 per year.

Among the smallest of cetaceans, the harbor porpoise rarely reaches 5 ft (1.5 m) in length, and mature animals do not weigh more than 140 lb. They have a short, barely distinguishable beak, and a low, triangular dorsal fin. They are dark gray above and lighter below, and may have gray streaking on the throat. Harbor porpoises do not follow ships, and are usually difficult to see because they surface so inconspicuously. They feed mostly on small schooling fishes. The name "porpoise" is derived from the Latin porcus pisces, which can be translated as "pig-fish," and among the local Newfoundland names for this species are "puffing pig" and "herring hog." In Dutch, this species is known as bruinvisch, in French it is marsouin commun, in Danish marsvin, in German schweinswal, and in Swedish tum-lare. Phocoena (pronounced "fo-seen-a") is the most common cetacean in European waters, and is also found in the inshore waters of the western North Atlantic and the North Pacific. It is sometimes encountered around river mouths, and goes upstream in various European rivers, including the Seine, the Thames, and the Danube. In the Lille Belt between the Baltic and North Seas, 17th- and 18th-century fishermen caught as many as 3000 porpoises in a single winter season, and there is still a drive fishery for this species in the waters of West Greenland. Otherwise, the two major predators of harbor porpoises are great white sharks and killer whales. Harbor porpoises are frequently entangled in fishermen's nets, and they have been heavily impacted by organochlorine pesticides and heavy metals.

One of the fastest of the small cetaceans, Dall's porpoise dashes through the water approaching vessels underway, then zooms away, sending up a "rooster tail" of spray. Estimates of its maximum speed are as high as 55 km h-1 (34 mph), but this is only for short bursts. It is found only in the North Pacific, from California up through Alaska and Kamchatka, south to Japan, and in the Sea of Okhotsk and the Bering Sea north of the Aleutians. There are two predominant color phases, the Dalli phase and the Truei phase, which differ most obviously in the anterior extent of the white patch on the flanks and belly, but they are now all included as one species. (There are also all black, all gray, and all white phases, but these are very rare.) Males grow larger than females, and have been measured at 7 ft and 10 inches (2.39 m) in length, and weighing 440 lb (200 kg). Dall's porpoise has the characteristic spade-shaped teeth of the true porpoises (Phocoenidae), but it also has "gum teeth," which project over the actual teeth, and may help the porpoise to grasp the small fishes and squid that make up its diet. In Russian this species is known as belokry-laya, and in Japanese it is ishi-iruka. Thousands of ishi-iruka are killed every year in the Japanese offshore gillnet fisheries, and thousands more are killed deliberately for food.

Richard Ellis

See also Killer Whale; Pilot Whale Further Reading

Ellis, R., Dolphins and Porpoises, New York: Knopf, 1982 Houck, W.J. & T.A. Jefferson, "Dall's porpoise Phocoenoides dalli." In Handbook of Marine Mammals, Volume 6, The Second Book of Dolphins and Porpoises, edited by S.H. Ridgway & R. Harrison, San Diego: Academic Press, 1999, pp. 443-472

Jefferson, T.A. "Dall's Porpoise." In Encyclopedia of Marine Mammals, edited by W.F. Perrin, B. Wursig & J.G.M. Thewissen, London and San Diego: Academic Press, 2002 Read, A.J., "Phocoena phocoena (Linnaeus, 1758)." In Handbook of Marine Mammals, Volume 6, The Second Book of Dolphins and Porpoises, edited by S.H. Ridgway & R. Harrison, San Diego: Academic Press, 1999, pp. 323-355 Reeves, R.R., C. Smeenk, R.L. Brownell & C.C. Kinze, "Atlantic white-sided dolphin Lagenorhynchus acutus (Gray, 1828)." In Handbook of Marine Mammals, Volume 6, The Second Book of Dolphins and Porpoises, edited by S.H. Ridgway & R. Harrison, San Diego: Academic Press, 1999, pp. 31-56 Reeves, R.R., C. Smeenk, C.C. Kinze, R.L. Brownell & J. Lien, "White-beaked dolphin Lagenorhynchus albirostris (Gray, 1846)." In Handbook of Marine Mammals, Volume 6, The Second Book of Dolphins and Porpoises, edited by S.H. Ridgway & R. Harrison, San Diego:Academic Press, 1999, pp. 1-30

Was this article helpful?

+1 0
Tube Jacker

Tube Jacker

Download Tube Jacker And Discover Everything You Need To Know About Jacking Unlimited Traffic From The Video Giant. The drop dead easy way to create winning video campaigns that will FLOOD your website with unstoppable FREE traffic, all on complete and total autopilot. How to exploit a sneaky method of boosting exposure and getting your videos to the top of Google within 72 hours, guaranteed.

Get My Free Ebook


Responses

  • gerontius
    Can dolphins live in the canadian high arctic?
    9 months ago

Post a comment