CHAPTER XIV

SHARKS--THE TIGERS OF THE SEA

Only a rapid systematic sketch of the class Pisces, fishes, is possible, distinguishing the main divisions, alluding to their history, and touching here and there the most characteristic genera and species of the thousands that have been described by ichthyologists. The primary division is into three subclasses:

1. _Elasmobranchii_--Sharks, skates, rays, etc., having a cartilaginous skeleton. 2. _Teleostomi_--Ordinary fishes, having a bony skeleton. 3. _Dipnoi_--Lepidosiren, and many extinct, primitive families.

In the Elasmobranchii, or selachians, the skeleton consists of cartilage, as in the embryos of all fishes--a sign of their primitive and inferior rank; but parts of it in various species become hardened by depositions of lime, especially in the vertebræ, in spines and teeth, parts often well preserved as fossils. Sharks' teeth are among the best known of fossils, and before science established their true character were commonly called "birds' tongues," or "snakes' tongues." The sharks, first to be considered, are a very ancient race, originating in early Paleozoic times. Of the many curious extinct forms that terrorized the Silurian, Devonian, and Carboniferous seas, a few representatives still exist in the South Pacific, notably the cow sharks; an eellike Japanese species with frilled gills that Dr. Garman thought might easily fill the rôle of "sea serpent"; and the quaint bullhead, or Port Jackson sharks of Australian waters; all these are of small size and the last named represents the principal race in Mesozoic seas. Their flat teeth form a sort of pavement of the mouth, enabling them to crush the mollusks and crabs on which they chiefly feed.

Next in a rising order of classification, and of somewhat more recent origin geologically, is the European family of dogfishes (Scyllidæ), which includes also the "ground sharks" of warm seas--deep-water fish eight to twelve feet long, that creep about near the bottom in search of prey. Next come the large pelagic sharks of the family Carchariidæ, which contains about sixty species, scattered over all the seas, and one confined in the fresh water of Lake Nicaragua. One section, that of the "topes" and "hounds" of temperate and warm seas, are bottom-feeders, and have pavementlike teeth adapted to crushing and grinding the shellfish on which they subsist; but most of the family are swift and powerful hunters of fishes in the open sea, such as the dreaded tiger shark of the West Indies, which is variegated in color and sometimes twenty feet long, and the equally big blue, white, dusky, and other ferocious bandits ranging not only the tropical seas, but more common in northern oceans than is generally supposed. The teeth in these and other hunting, fish-catching sharks, are shaped somewhat like arrowheads, in some cases smooth-edged and single-pointed, in others with sharply notched edges and side cusps. They are set in the flesh of the jaw, unattached to the underlying bones, in concentric rows, one close behind the other, all round the front of the mouth, both above and below, and look and act like a set of saws, a sidewise movement of the jaws sawing through an object seized in a single bite. As fast as the front row of teeth are lost they are replaced by those of the row immediately in the rear. But all gradations exist between these and the mosaic of "pavement" teeth in the topes. The mouth of these hunting sharks is on the underside of the head, and they must turn on their backs to seize anything floating or swimming near the surface.

This is the group that furnishes the "man-eater" stories--tales that have been substantiated by so many terrifying examples that no precaution of safety against them should neglected, even on our northern coasts, where the ravenous blue shark, or the dusky species, may appear at any time, even in harbors. A few years ago a man was seized by one of these sharks in a little inlet of New York Bay, at Freeport, New Jersey.

Blue sharks are nocturnal in habit, and are sometimes seen asleep or resting in the daytime, with the tips of the two dorsal fins, characteristic of this family, in sight above the surface of the water. "So gentle are they in their movements," says one authority, "that, unlike many other monsters of the deep, they do not disturb the luminous creatures, which at the same time will be lighting every wavelet with their phosphorescence. Blue sharks are not very particular as to what fish they take as food, though those which are gregarious in their habits, like mackerel, pilchards, and herring, are most commonly hunted by them." A curious relative of these "man-eaters" is the hammerhead, in which the sides of the head are extended in two great lobes, with eyes at their extremities; this kind of shark is greatly feared in the East Indian seas. In spite of it, and the prevalence of other huge and voracious sharks, the Arabs about the entrance to the Red Sea, and the natives of other Oriental shores, will swim and dive in the open sea, apparently without fear, where Europeans would be devoured almost instantly. Another peculiar shark is the thresher, well known in the North Atlantic as elsewhere for its strategic maneuvers. It grows to a length of fifteen feet, of which the tail forms at least one half. Quite inoffensive to man, the thresher feeds on the shoals of smaller teleosts, such as pilchards, herrings, and sprats. When feeding it swims in gradually diminishing circles around the shoal, splashing the water with its long tail, and keeping the victims so crowded together that they become an easy prey. Hammerheads and their relatives, the "bonnet" sharks, frequently visit both our shores in summer.

The porbeagles are big, fierce sharks of the family Lamniidæ, the giant of which is Rondelet's shark, known to attain a length of more than forty feet. The triangular, saw-edged teeth of such a one measure nearly an inch across the base; but similar fossil teeth, and also others dredged from the bottom of the South Pacific, are much larger, indicating sharks beside which Rondelet's would be small, and in all probability these monsters survived to a comparatively recent date. A remarkable lamnoid shark of Japanese deep waters has the snout produced into a long, flat, flexible, leaflike blade.

Closely related sharks, almost as big, are well known in the North Atlantic. Two of them, the "bone" and the "basking" sharks, are killed by fishermen whenever encountered for the sake of the oil in their livers. The name of the second refers to its habit of loafing and sleeping on the surface on fine days, when a boat may go so near it that a harpoon may be planted in its hide before it will move. The real "basking shark," however, is a gigantic species of Rhinodon, of the Indian and South Pacific oceans, with a very bulky body that may exceed forty-five feet in length. Both of these ponderous fishes are sluggish, and are not dangerous to man, except that a blow of the tail may smash a boat when an attempt is made to harpoon them at close quarters. They feed on small fishes that go in shoals, and also, perhaps, on seaweeds.

The last sharks to be mentioned are American dogfish of the family Squalidæ (another family, Scyllidæ, are known as "dogfish" and "hounds" in Great Britain), which are numerous and greatly hated along both our northern coasts. The common gray dogfish of the North Atlantic and California coasts is the spiny one (_Squalus acanthias_), the larger females of which will weigh about eight pounds. It makes its home in deep water off the New England coast, approaching the shore when the mackerel come in and disappearing when they depart; but dogfish are to be found all summer in shoal places such as George's Bank, and irregularly in shore inlets. In the late autumn they become numerous on the Grand Banks, and stay there until the winter's cold drives them away into deeper water. Everywhere these small sharks are a nuisance to the fishermen, by tearing nets and by eating the cod, etc., hooked on the trawl lines. Formerly they were regularly hunted for the oil in their livers, which is especially valuable for certain purposes, as in harness making, but the price of this oil is now low, and the fishery has declined.

The economic use of sharks is not great except as producers of oil. The flesh is good food, but not popular. In China sharks' fins are a favorite substance for delicate soups and sauces, and a very large trade in catching sharks for their fins is carried on near Bombay, and in East Indian waters.

The ugly angel shark, with its squat, toadlike body, big, winglike side fins and thick tail, occupies an intermediate place between the sharks and the rays. It creeps along the bottom, and is remarkably voracious. The chimæra is another queer "monster" of the deep.