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Porbeagle Shark

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Porbeagle Shark
Lamna nasus

Photo modified from Sharks and Rays. TC Tricas, K Deacon, P Last, JE McCosker, TI Walker, L Taylor. 1997. Nature Company Guides, Time Life Book Series. Weldon Owen Pty Ltd San Francisco.

   The porbeagle is a stout shark that is blue-gray on top and white underneath with a white patch on the trailing edge of the first dorsal fin. It has a crescent shaped tail and a secondary keel that effectively cuts the water during the side to side swimming motion. Adults can attain a size of 3.7 meters (12 feet), and have an average life expectancy of 30 to 40 years. This shark has relatively large eyes. The teeth in the moderately sized mouth are similar in both the upper and lower jaw (they are smooth-edged with lateral denticles), although young individuals may lack the lateral denticles.


Photo from the Canadian Shark Research Laboratory web site

   The porbeagle has a heat regulating mechanism that raises the body temperature 2.7 to 8.3 degrees Celsius above the surrounding water temperature. This allows the shark to operate more efficiently in the cooler waters it inhabits. Unlike many other sharks the porbeagle must swim at all times in order to breathe.

Diet

   The porbeagle feeds mainly upon pelagic fishes such as herring, lancetfish and mackerel. However they also eat cod, redfish, haddock, squid and shellfish.

Reproduction

   The porbeagle is ovoviviparous, retaining the developing young within the brood chamber before giving birth to live young. The developing sharks obtain nutrients by devouring other fertilized eggs in the oviduct. Young are probably born in the late winter and spring. The females generally produce 4 pups that are between 60 to 75 cm long at birth. Female porbeagles reach sexual maturity at an age of 12 years or older, while the males are mature at age 7.


A porbeagle shark embryo.

Habitat

   The porbeagle shark is common in pelagic and littoral zones, and inhabits water down to a depth of 370 meters (1,120 feet). It is most commonly found on continental shelves or inshore. It prefers cool waters and is usually found in temperatures below 14 degrees Celsius.

Range

   Porbeagles occur on both sides of the Atlantic, and in the south Pacific and Indian Oceans. In the western North Atlantic it can be found from Raleigh, Newfoundland at its northernmost range to the Gulf of St. Lawrence, the Scotian Shelf, the Bay of Fundy and the Gulf of Maine to New Jersey and perhaps to South Carolina. Off Nova Scotia the porbeagle is generally found in waters less than 14 degrees Celsius.

Distinguishing Characteristics

  • White patch on the trailing edge of the first dorsal fin
  • Caudal fin with secondary keel
  • Lateral denticles on the teeth
  • Lunate tail
Lateral denticles in porbeagle teeth are not found in the teeth of a mako
Primary and secondary keels on porbeagle tail distinguish it from a mako, which lacks the secondary keel

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