Thalassians, or Sea Tortoises.
Cheloniadæ, Gray; Carettoidæ, Fitzing; Halychelones, Kelgen; Oiocopodæ, Wagler.
The Turtles or Sea Tortoises are distinguished from all others by a comparatively flat carapace, long members, the extremities of which terminate in broad paddles, the anterior much longer than the posterior ones; the toes, though formed of distinct pieces, can only act together, thus constituting true oars, admirably arranged for swimming. Their carapace, besides being flat, is indented and elongated in front, and contracted behind, being disposed in such a manner that the head and feet can be completely hidden.
Marine Tortoises are the largest of their species: they swim and dive with great facility, and can remain long under water. The external orifice of the nasal canal is furnished with a sort of valve, which the animal raises when it is in the air and closes when under water; but it rarely leaves its liquid element except in the breeding season, when nature prompts it to seek the shore to lay its eggs. Some of the species, however, seek the shore in the night, when they frequent the banks of desert and solitary isles, where they browse on marine plants. Although they walk with difficulty, and even with pain, in quiet seas they may be seen floating like a boat, in absolute immobility, and asleep on the surface of the water. With their horny jaws, which are hard and trenchant as the beak of a bird of prey, some of them feed upon sea-weed and algæ, while others feed on living animals, such as crustaceans, zoophytes, and mollusks.
We have seen how regularly and systematically the Land Tortoises proceed in depositing their eggs—nor is less precaution taken by the Sea Tortoise. The females, accompanied by the males, traverse several hundreds of miles of sea in order to deposit their eggs in some favoured locality. Other females resort, year after year, almost to a day, to the sandy shore of some desert isle, where they drag themselves ashore during the night, sufficiently inland to be safe from the tide. In some such spot, using their hind feet by way of a shovel, they excavate holes about thirty inches deep. Here they lay frequently a hundred eggs, covering them up afterwards with the fine sand, levelling the surface, and then returning to sea, leaving the eggs to be hatched by the solar rays. The eggs are round, slightly depressed at both ends, and furnished with a coriaceous shell. From the high temperature communicated to the sand-bank, they are hatched in about fifteen days. The females seem to have two or three layings in the season, at intervals of two or three weeks. When the young Turtles are hatched, they are feeble, white, and about the size of frogs, and their instincts lead them at once to the sea. Under the fostering care of their mother, those which have escaped the birds of prey on their way to the sea, and the fishes lying in wait for them, rapidly develop, and attain, under favourable circumstances, an enormous size,—some of the Sphargis, or Soft Turtles, having been known to weigh from fifteen to sixteen hundred pounds,—while others, whose carapaces measured more than fifteen feet in circumference and seven feet in length, exceeded eighteen hundred pounds.
Marine Tortoises are met with in herds more or less numerous in all seas, principally towards the torrid zone in the tropical regions, on the shores of the Antilles, in Cuba, Jamaica, St. Domingo, the Gulf of Mexico, and in the Indian Ocean. Those occasionally found by navigators in the North Atlantic and Mediterranean seem to be wanderers separated from some travelling bands.
Fig. 40.—Green Turtle (Chelonia Mydas).
Of all reptiles, the Sea Tortoise is the most useful to man. In countries where they are common, and where they attain an enormous size, their flesh is the most healthy and nourishing food, and their carapace serves as a canoe in which the natives paddle along the shores. They even roof their huts with them; they convert them into drinking-troughs for their cattle and into baths for their children. According to Strabo and Pliny, the ancient inhabitants of the shores of the Indian Ocean and the Red Sea converted the enormous carapaces of the Tortoise which frequented their shores into coverings for their houses, and boats for paddling along the coast. The fat of many species, when fresh, is used as a substitute for oil and butter. When the musk-like odour of this fatty substance, as in Chelonia caouana and C. caretta, becomes too repulsive for food, it is employed in embrocations, in tanning leather, or in lamps. The eggs of nearly all the Turtles are sought after for their flavour. Finally, the carapace of several species constitutes a valuable material much employed in the arts, and known as tortoise-shell. This material is sought after in consequence of its hardness and the fine polish of which it is susceptible, and also for the facility with which it is worked. It has a strong resemblance to horn, but is easily distinguished from it. Though, like horn, it is formed of parallel fibres, it seems to be rather the result of exudation, consisting of a kind of solidified mucus. Its texture is homogeneous; it can be cut and polished with precision and beauty; in short, under the influence of a gentle heat, it is softened and can be modelled into any fashion, according to the taste of the moulder; after becoming cool it retains the desired shape.
Fig. 41.—Capturing Turtles.
While most of the Tortoises are highly useful to man, both for food and other purposes, perhaps the most interesting are the Green Turtles (Tortues franches of French authors), Chelonia caouana and Caretta. From these man draws the greatest advantage from their superior size, and from the thickness of their shells. The Green Turtle (Chelonia Mydas, [Fig. 40]) is so called from the reflected green of its carapace. It abounds in the Southern Atlantic Ocean, where it keeps habitually far from the shore, except in the breeding seasons, when it makes long voyages in order to deposit its eggs, giving a preference for that purpose to Ascension Island and St. Vincent. It rests on the surface of the open sea, and as it sleeps heavily, it is easily taken by a cord with a running knot, which is carefully slipped round its neck as the boat containing the captors silently glides past. It is even said to be a practice with the Malay fishermen to dive beneath them, and attaching a cord to the foot of a sleeping Turtle, thus take it alive.
Many other modes are employed for capturing them. In the regions frequented by them in the breeding season, they are followed by their track on the sands, and their retreat cut off, when met with, by forming a circle round them, when they are thrown on their backs; hand-spikes sometimes being necessary to accomplish this from their great size. In this position they are helpless, and must remain until wanted, so that their enemies have time to pursue their sport elsewhere, as represented in [Fig. 41]. The next day they are collected or destroyed at leisure. In 1802 the crew of a French ship surprised a female Turtle on the Island of Lobos. The men had infinite trouble in making good its capture and throwing it on its back, for it was strong enough to drag them all towards the sea. It was at last mastered. Its head was as large as that of an infant, and its beak four times the size of a paroquet. It weighed two hundred and sixty pounds, and had in its body three hundred and forty-seven eggs. Turtles are also taken in nets, in the meshes of which their beaks and flippers get entangled; thus prevented from coming to the surface for air, they die of asphyxia. Others harpoon them on the open sea when they come to the surface to breathe. The harpoon is attached to a cord, by which the animal is soon brought to the surface and drawn into the boat. But the commonest mode of capture is approaching them in a boat as they float asleep on the surface—this must be done silently. When within reach, a back flipper is laid hold of by one of the crew, and by a sudden twist the Turtle is thrown on its back, when becoming helpless for the moment, it is dragged on board.
Fig. 42.—Hawk's-bill Turtle (Chelonia caretta).
A very curious mode of fishing for Turtle is pursued by means of small fish, a species of Echeneis or Remora. These small fish are provided with an oval plate on the head, which consists of a score of parallel plates, forming two series, furnished on their outer edge with an oval disk, soft and fleshy at its circumference; in the middle of this plate is a complicated apparatus of bony pieces dispersed across the surface, which can be moved on their axis by particular muscles, their free edges being furnished with small hooks, which are all raised at once like the points of a wool-card. The fishermen keep many of these fishes in buckets of water. When they see a sleeping Turtle they approach it, and throw one of these suck-fish into the sea. The fish dives under the Turtle, and fixes itself inextricably to it by means of their cephalic disk. As the fish is attached to a long cord by means of a ring in its tail, the fish is drawn on board along with its victim. This is line fishing of a new kind, in which the hook is living, and pursues its prey in the bosom of the deep.
The Green Turtle, whose flesh is celebrated for its delicacy and excellence of its fat, is that from which Turtle soup is made. Turtle soup is only of recent invention, the first Turtle having been brought to London by Admiral Anson in 1752. It was long a costly dish, and even now, although the introduction of steam and other adjuncts to navigation has greatly modified the expense, its price is about ten shillings per pound weight.
Fig. 43.—Loggerhead Turtle (Chelonia caouana).
Much of the tortoise-shell of commerce comes from the Green Turtle, but by far the finest specimens are produced by the Imbricated or Hawk's-bill Turtle, Chelonia caretta ([Fig. 42]). In this species the plates of the disk are imbricated, or lapping over each other, and thirteen in number. The muzzle is long and compressed; the jaws with straight edges, without dentation, curving slightly towards each other at their extremities, with two nails on each fin. It rarely attains the size or weight of the Green Turtle. The Hawk's-bill Turtle is met with in the Indian Ocean, and also on the American shores. It feeds on marine plants, on mollusks, and small fishes, and is chiefly sought after for its shell, which produces the finest tortoise-shell known; while its flesh is rendered unpalatable from its musky flavour. On the other hand, its eggs are excellent when fresh, and eagerly sought after.
In order to prepare the shell, it is softened by means of boiling after being torn from the animal's back. It is then flattened by being passed through a press, previous to being polished. In this condition it is ready for all sorts of ornamental work. The Loggerhead Turtle, or C. caouana ([Fig. 43]), like the Green Turtle, has its scales placed side by side. Its colour is brownish or deep maroon. It is found incidentally on the French and English coasts, and abounds in the Atlantic and Mediterranean seas. Its length is about four feet; its weight, from three to four hundred pounds. It is very voracious, and feeds principally on mollusks. Its shell is much valued, but its flesh is indifferent, and its fat altogether uneatable; however, it is used in some localities to make lamp-oil.
Fig. 44.—Leather-back or Corded Tortoise (Spargis coriacea).
The Leather-back or Corded Tortoise, Spargis coriacea, differs from every other genus, its body being enveloped in a coriaceous hide; tuberculous in the young, perfectly smooth in adults. The feet are without claws. Seven longitudinal grooves extend from the neck to the tail, which remind one of the seven chords of the ancient lyre. Only one species of Sphargis is known (S. coriacea, [Fig. 44]). This species is found in the Mediterranean and Atlantic Ocean, and is, with the Hawk's-bill Tortoise, the only species found on the British coast. Its body is a light brown, with the lines of the carapace fawn-colour; its members black, edged with yellow. It attains the length of six to eight feet, and a breadth of about one-fifth of the length: it sometimes attains the weight of fourteen to sixteen hundred pounds. Its flesh is said to be unwholesome, and, on being eaten, to produce severe vomiting and purging.