page_title: Porbeagle
section_title: Description
hierarchical_section_title: Porbeagle / Description
caption_attribution_description: English: Porbeagle (Lamna nasus)
context_page_description: The porbeagle 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. The porbeagle typically reaches 2.5 m in length and a weight of 135 kg; 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 at the aft base of its first dorsal fin, and the two pairs of lateral keels on its tail.
  The porbeagle is an opportunistic hunter that preys mainly on bony fishes and cephalopods throughout the water column, including the bottom.
context_section_description: The porbeagle is a very stout-bodied shark with a fusiform (spindle-like) shape. The long, conical snout tapers to a sharp point, and is supported by enlarged, highly calcified rostral cartilages. The eyes are large and black, without nictitating membranes (protective third eyelids). The small, S-shaped nostrils are positioned in front of and below the level of the eyes. The mouth is large and strongly curved, with moderately protrusible jaws. North Atlantic sharks have 28–29 upper tooth rows and 26–27 lower tooth rows, while Southern Hemisphere sharks have 30–31 upper tooth rows and 27–29 lower tooth rows. Each tooth has a strongly arched base and a nearly straight, awl-like central cusp, which is flanked by a pair of smaller cusplets in all but the smallest individuals. The five pairs of gill slits are long and precede the pectoral fin bases.
  The pectoral fins are long and narrow. The first dorsal fin is large and high, with a rounded apex, and originating just behind the pectoral fin bases. The pelvic fins are much smaller than the first dorsal fin. The second dorsal and anal fins are smaller still, and placed about even with each other on narrow bases that allow pivoting from side to side. The sides of the caudal peduncle are expanded into prominent lateral keels. A second, shorter pair of keels are present below the main keels. The caudal fin is large and crescent-shaped, with the lower lobe almost as long as the upper;  both dorsal and ventral depressions (precaudal pits) are at the caudal fin base, and a deep ventral notch is near the tip of the upper caudal fin lobe. The skin is soft and covered by tiny, flattened dermal denticles (scales), lending a velvety texture. Each denticle has three horizontal ridges that lead to teeth on the posterior margin.
  The dorsal coloration is a medium to dark gray or slate, extending to the bases of the pectoral fins. The underside is white; adults in the Southern Hemisphere often have dark coloring under the head and dusky blotches scattered over the belly. The free rear tip of the first dorsal fin is abruptly light gray or white, a feature unique to this species. The porbeagle may attain a length of 3.7 m (12 ft), though this is uncertain and may have resulted from confusion with other mackerel shark species. A more typical length is 2.5 m (8.2 ft). Female sharks grow larger than males in the North Atlantic, with maximum confirmed fork lengths (snout tip to caudal fin fork) of 2.5 m (8.2 ft) for males and 3.0 m (9.8 ft) for females. Southern Hemisphere sharks are smaller and the two sexes are similar in size, with males and females attaining fork lengths of 2.0 m (6.6 ft) and 2.1 m (6.9 ft) respectively. Most porbeagles weigh no more than 135 kg (298 lb), with the record being a 230 kg (510 lb) individual caught off Caithness, Scotland, in 1993.
caption: A Southern Hemisphere porbeagle showing the white patch on the rear tip of the first dorsal fin, which is unique to the species.
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