- published: 20 Dec 2015
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The porbeagle (Lamna nasus) is a species of mackerel shark in the family Lamnidae, distributed widely in the cold and temperate marine waters of the North Atlantic and Southern Hemisphere. In the North Pacific, its ecological equivalent is the closely related salmon shark (L. ditropis). The porbeagle typically reaches 2.5 m (8.2 ft) in length and a weight of 135 kg (300 lb); North Atlantic sharks grow larger than Southern Hemisphere sharks and differ in coloration and aspects of life history. Gray above and white below, the porbeagle has a very stout midsection that tapers towards the long, pointed snout and the narrow base of the tail. It has large pectoral and first dorsal fins, tiny pelvic, second dorsal, and anal fins, and a crescent-shaped caudal fin. The most distinctive features of this species are its three-cusped teeth, the white blotch on the back of its first dorsal fin, and the two pairs of lateral keels on its tail.
Preying mainly on bony fishes and cephalopods, the porbeagle is an opportunistic hunter that regularly moves up and down in the water column, catching prey in midwater as well as off the bottom. It is most commonly found over food-rich banks on the outer continental shelf, but does make occasional forays close to shore or into the open ocean, down to a depth of 1,360 m (4,460 ft). It also conducts long-distance seasonal migrations, generally shifting between shallower and deeper water. The porbeagle is fast and highly active, with physiological adaptations that enable it to maintain a higher body temperature than the surrounding water. It can be solitary or gregarious, and has been known to perform seemingly playful behavior. This shark is aplacental viviparous with oophagy, meaning that the developing embryos are retained within the mother's uterus and subsist on non-viable eggs. Females typically bear four pups every year.