Author: Müller and Henle, 1838
Field Marks:
Large sharks with pointed snouts and spindle-shaped bodies, long mouths with large, bladelike teeth, long gill slits, long pectoral fins and high first dorsal fins, small, pivoting second dorsal and anal fins, large lateral keels and prominent precaudal pits on the caudal peduncle, and lunate caudal fins.
Diagnostic Features:
Trunk fusiform and moderately slender to very stout. Head moderately long but shorter than trunk; snout moderately long, pointed and conical, not greatly elongated, flattened and bladelike; eyes moderately large; mouth large, ventral on head, gill openings large, extending onto dorsal surface of head, all anterior to pectoral fin bases; no gillrakers on internal gill slits; teeth large, anteriors and laterals narrow and awl or bladelike to broad, compressed and triangular, less than 85 rows in either jaw; two rows of large anterior teeth in each jaw, the uppers separated from the upper lateral teeth by one row of small intermediate teeth on each side. First dorsal fin large, high, erect and angular or somewhat rounded; second dorsal and anal fins minute, much smaller than first dorsal fin, with narrows pivoting bases; pectoral fins very long and narrow, shorter to about as long as head in adults; pelvic fins small, much smaller than first dorsal fin but larger than second dorsal and anal fins; caudal fin lunate, upper lobe moderately long, less than one third as long as rest of shark, lower lobe long and strong, nearly as long as upper lobe. Precaudal pits present, caudal peduncle strongly depressed and with strong, high keels.
Habitat, Distribution and Biology:
Lamnids are tropical to cold-temperate, littoral to epipelagic sharks with a broad geographic distribution in virtually all seas, in continental and insular waters from the surf line to the outer shelves and rarely down the slopes to at least 1280 m. All the living species are of large size, with a maximum length of 3 to at least 6.4 m; a giant, rather recently (late Pliocene) extinct member of the white shark genus (Carcharodon megalodon) attained as estimated length of about 12.4 m.
These sharks are fast-swimming, active pelagic and epibenthic swimmers, some of which are capable of swift dashes and spectacular jumps when chasing their prey. Mackerel sharks are partially warm-blooded, and have a modified circulatory system that enables them to retain a body temperature warmer than the surrounding water. This permits a higher level of activity and increases the power of their muscles. They feed on a wide variety of bony fishes, other sharks, rays, marine birds and reptiles, marine mammals, squids, bottom crustaceans, and carrion. Development is ovoviviparous, without a yolk-sac placenta. Like other lamnoid sharks where reproduction is known these sharks have oophagy or uterine cannibalism, in which developing fetuses feed on fertilized eggs and possibly smaller siblings for a long time before birth.
Lamnids of the genus Lamna are apparently inoffensive but are considered potentially dangerous to people because of their size and relatively large teeth. At least one member of the genus Isurus (shortfin mako) has been indicted in a few attacks on swimmers and divers, but has attacked boats several times; the other species (longfin mako) has never been recorded as attacking people or boats. However, this family contains what is generally considered the most dangerous shark, the great white (Carcharodon), because of numerous attacks by it on swimmers, divers, surfers and boats.
Interest to Fisheries:
These sharks are important objects of fisheries because of their fine meat, but are also utilized for oil, fins, hides, fishmeal, jaws and teeth. Some species are oceanic in whole or part, and are mainly taken with pelagic longlines; gillnets, hook-and-line, and even harpoons, pelagic and bottom trawls are used to capture these sharks.
Remarks:
Reviews of this family are in Bigelow and Schroeder-(1948), Garrick and Schultz (1963), Farquhar (1963), and Bass, d'Aubrey and Kistnasamy (1975b).
Pratt and Cascy (1983) estimated the age of the shortfin mako, Isurus oxyrinchus, using four methods. As with Parker and Stott's (1965) work with the basking shark, Cetorhinus maximus, these authors assume two growth rings per year on mako vertebrae from indirect calibration methods.