In the same family with Carcharodon, and distinguished therefrom by having the edges of the teeth entire instead of serrate, are the mackerel sharks, of which four species may be found on the Atlantic coast (all of these are now placed in the genus Isurus by Garman; The Plagiostomia, 1913). One of these (4), a cosmopolitan species in temperate latitudes, is the “porbeagle” of England (Lamna nasus). It attains a length of ten to twelve feet. The common species on the east coast of the United States is the “blue shark” of the Cape Cod fishermen, readily distinguishable by the large black spot on the pectoral fin. It reaches a length of eight to ten feet. The mackerel sharks are handsome, trim, and active species, and are so named because they are present chiefly during the mackerel season and prey largely on that fish. They are sometimes very annoying to purse-seine, pound-net, and gill-net fishermen.
Related to the mackerel sharks anatomically, but differing markedly from them in habits and disposition, is the basking shark or bone shark (Cetorhinus maximus). These names have been applied by our fishermen in allusion to the facts that the fish often remains quiet at the surface for a long time and that the gill arches are provided with strainers which resemble whalebone. This fish was described by the Norwegian bishop Gunner in 1765 in a learned paper in which he sought to prove that this must have been the “great fish” that swallowed Jonah. From the standpoint of mere size, the basking shark fulfills all the requirements, for it is one of the largest of sharks and the ingestion of a prophet would have entailed no difficulty or inconvenience. A length of fifty feet has been claimed for it, but the available authentic records give a maximum of under forty feet. It is at home in the Arctic seas, but sometimes has strayed as far southward as Virginia and California. In former years it was not uncommon on the New England coast and also on the shores of western Europe; and it was regularly hunted for its oil in Ireland and Norway. In the early eighteenth century, and in the early part of the last century, it was not infrequently harpooned by the Maine and Massachusetts fishermen, and the liver of a large specimen has been known to yield twelve barrels of oil. From Eastport, Maine, and Provincetown, Massachusetts, and even from the lower harbor of New York, quite a number of individuals ranging from twenty-eight to thirty-five feet in length have been reported, but recently the species is rare in our waters. Its disposition is peaceful, and it is dangerous only because of its great bulk. When attacked, its powerful tail easily demolishes boats, and its pursuit has been attended by considerable excitement and risk.
The thrasher or swingle-tail (Alopias vulpinus) is another large and active pelagic shark which is common along the coasts of New England and western and southern Europe, and is known also from California. It is at once distinguished from all other sharks by its prodigious tail, the tipper lobe of which, in the form of a scythe blade, is half the total length of the fish. The fishermen tell tales of the ferocity of this shark in attacking whales, which, when they come to the surface to breathe, are said to be flailed by the thrasher’s flexible tail, so that the resounding whacks may be heard for several miles in calm weather. Authentic observations of this habit are lacking. The species is certainly harmless for man, in spite of its large size—it attains a length of fifteen feet and a weight of five hundred pounds. It is a source of some annoyance to our mackerel fishermen because it often becomes entangled in the nets. In July, 1904, an imperfect skeleton of this fish about ten and one-half feet long, with cranium and two hundred and seventy-four vertebrae, was exhibited at Atlantic City, as that of a “sea serpent,” and an impossible account of its capture was published in the local newspapers at the time (for identity of this skeleton, see note by the writer in Forest and Stream, December 3, 1904).
In strong contrast with the striking modification of the tail in the foregoing species, the hammer-head and the bonnet-head sharks (Sphyrna zygaena and S. tiburo), present grotesque lateral expansions of the head. Both species range from the tropics along our east coast as far as Massachusetts. The former is a voracious species and, attaining a length of more than fifteen feet, is formidable to man; the latter, much the commoner on our South Atlantic coast, rarely exceeds five feet in length. Mitchill’s Fishes of New York records the capture of three hammer-heads in a net at Riverhead, New York, September, 1805; the largest, eleven feet long, contained the detached remains of a man and also a striped cotton shirt.
The sand shark (Carcharias taurus) is one of the best-known sharks of our Atlantic coast. It is sometimes called “shovel-nose shark” and “dogfish shark” on the shores of New England. Its usual length is under five feet, but it is said, perhaps on account of error in identification, to attain a length of twelve feet and a weight of two hundred and fifty pounds. It is built on rakish lines, its snout is sharp, its crescentic mouth is armed with long and narrow teeth, the fishermen say it has a wicked eye, and its disposition is vicious. It is able to do very serious injury to careless fishermen who are trying to remove it from their nets or boats, and the writer has seen it inflict fearful wounds on other species of sharks confined with it in the observation pool at Woods Hole, Massachusetts.
The largest family of sharks in our waters is the Carcharinidae.(5) The many genera however are not always easily distinguishable until the teeth and dermal denticles are carefully examined (see illustration).
Two of the most interesting are the blue shark (Mustelus canis), a world-wide species attaining a moderate size, characterized by the very dark blue color of the upper parts; and the tiger shark, or leopard shark (Galeocerdo cuvier), an active, graceful, ferocious species, with razor-like teeth. The latter is known from Provincetown, Woods Hole, and other places on the Atlantic coast.(6)
Scientific names of fish are not always expressive of obvious habits or structure, but Somniosus microcephalus, or the “small-headed sleeper,” aptly describes a large boreal shark that makes occasional visits to our coasts as far south as Cape Cod and Oregon. Its body seems to have developed at the expense of its brain, for it is a sluggish stupid glutton that reaches a length of twenty-five to thirty feet. It is said to be a very active foe of whales. When caught in the fisheries of western Europe, the sleeper shark is brought in by the fishermen and offered for sale as food, although its market value is small. The writer has seen it in the markets of Grimsby, Cuxhaven, and Hamburg.