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ОглавлениеTHE NATURALIST AT SEA.
It is the opinion of most people that during the voyage to and fro between England and India but little opportunity of pursuing his favourite study presents itself to the naturalist. This is, in a sense, true. For when we consider the extent to which the ocean teems with animal life, when we reflect that every wave that breaks against the ship’s side contains hundreds of living organisms, we cannot but wonder that we, from the deck of the ship, do not see more of the inhabitants of the sea. A little consideration, however, will clear up the mystery. Animals that live in the ocean fall into two classes—deep-sea creatures and organisms which dwell near the surface.
The former class inhabit the cold waters of the lowest depths where the pressure is enormous, and where eternal darkness prevails. These animals never come to the surface, so that the ordinary traveller cannot hope to see any of them.
As regards the fauna of the surface, the naturalist is more fortunate. But here again several causes militate against him. There are two classes of animals which live near the surface; those creatures which are powerful swimmers and are able to travel whither they will—these are sometimes called the Nekton; and the smaller organisms whose natatory powers are but small, and which are at the mercy of the waves, being carried about hither and thither by wind and current. This group, which includes jelly-fish and small crustaceans, is often termed the Plankton. The Nekton are disturbed by the approach of the ship and hurry away from it, and thus mostly elude the observer’s gaze. Most of the Plankton, on the other hand, are so small as to be invisible to the naked eye; and the majority of them come to the surface only at night, descending some feet as soon as daylight approaches. The object of this daily migration is to enable these lowly organisms to make the most of the light. This habit of descending during the day allows them to search for food, both by day and by night. Were they to remain at the surface during the day, they would lose their only chance of obtaining food at a greater depth.
Of the remaining Plankton others are almost transparent, so that it is most difficult to see them when the sea is at all rough. But give him one of those heavenly days, so few and far between, such as March 6th, 1900, when the sea was as smooth as glass, and the naturalist desires nothing more. He has ample opportunity of studying marine life. But he must go right forward to the bow of the ship, where he can look down into the blue water as yet undisturbed by the rude contact of the fast-moving steamer. Magnificent jelly-fish may be seen in thousands, some almost perfectly transparent, others of a milky-white hue with pink patches. They float near the surface, moving most gracefully by the rhythmic contraction of their “bell” or “umbrella.” There is no more beautiful sight in nature than the movement of a medusa. Dozens of other Plankton may be seen on such a day, creatures of diverse form and size, displaying the most beautiful tints: deep red, orange, pink, brown, yellow, and blue. In half an hour the writer noticed no fewer than eleven different genera of such organisms—Medusæ Siphonophora, and Ctenophora.
Many of these surface-floating forms are phosphorescent. Such are best seen at night. Upon some evenings all the water disturbed by the boat assumes the appearance of liquid phosphorus. This phenomenon is due to the fact that many of the minute organisms in the water are phosphorescent. The commonest light-emitting creature is a tiny animal called Noctiluca. It is invisible to the naked eye and is usually cherry-shaped. Sometimes, however, its form is more like that of a kidney. From the depressed side there projects a short whip-like process, termed the flagellum, by the lashing of which the creature slowly forces itself through the water.
We now come to the Nekton, animals that are powerful swimmers, such as fish, whales, sharks, dolphins, and porpoises. Sharks abound in the tropical seas, as the condition of some of the unfortunate “have-a-dive” boys amply testifies. These evil fish, however, do not readily show themselves, and the traveller cannot expect at the best to see more than a dark fin.
Whales, dolphins, and porpoises are mammals which have taken to an aquatic life. A whale is no more a fish than a dog is. It breathes by lungs, not by gills. The female suckles her young. It possesses no fins, but swims by means of its legs which have become modified into flappers. Since lungs form the breathing organ of the whale, it must continually come to the surface in order to breathe. Then it is that the presence of the monster becomes known. The “spouting” of whales is part of the breathing process. When the whale wishes to take in a fresh supply of air he comes to the surface, and just before he reaches it makes a violent expiratory effort. Thus much air is forced out of his nostril, which, passing through water, reaches the atmosphere as a jet of spray. It is an error to imagine that the whale ejects water from its nostril.
Porpoises are common objects in the Indian Ocean. Like whales, they are mammals. They are usually seen in swarms or “schools,” which often accompany ships for considerable distances. As often as not the porpoises precede the ship, hence their object in accompanying it cannot be to catch stray particles of food. There appears, indeed, to be but one explanation of the phenomenon—the inquisitiveness of the porpoise. Curiosity is a common trait in animals. Take, for example, the oft-quoted cases of dogs and monkeys. There is but little doubt that the porpoise is naturally curious. A “school” sees a new and strange sight in the shape of a ship and turns aside to behold the wonder. No observer can fail to be impressed by the graceful movement of the porpoise and also by the great speed at which he travels through the water. For hours a porpoise will keep pace with a steamer, crossing and re-crossing her bows with the greatest impunity. Sometimes a school of porpoises advances in Indian file. In such a case, seen from a distance, they look like an enormous sea-serpent; each revolving porpoise appearing like a coil of the serpent’s body. This is possibly the origin of the sea-serpent myth.
Flying-fish are very common objects in the Red Sea and Indian Ocean, constantly jumping out of water when disturbed by the approach of the ship. These creatures have greatly enlarged wing-like pectoral fins. The tail is also of considerable magnitude. Fins and tail are the organs which assist these animals in their flight. A flying-fish jumps out of the water to a height of usually from two to three feet, and describes a parabolic curve until it touches the water, when it flaps its fins vigorously and again rises and performs a similar, but generally shorter curve. This process may be repeated several times before the fish finally disappears in the water. There is a considerable controversy raging on the question of the use of the fins to this fish in its flight. Some authorities declare that the fins act merely as a kind of parachute, enabling the creature to prolong its jump into the air. Others, however, assert that the animal flaps its fins while in the air, thus using them as a bird does its wings.
The writer had exceptional opportunities of closely observing flying-fish in the Indian Ocean during most unusually calm weather. While describing the parabolic curve in the air the creature never moves its fins. It is only when it touches the water again that it gives several vigorous flaps with its fins until it attains sufficient impetus for another flight. Seen from a distance, these fish certainly do seem to flap their fins in the air. This, however, is probably an optical illusion caused by the reflection of the sunlight from the fins as the creature sways from side to side during its flight. Flying-fish do not appear to remain longer than seventy or eighty seconds out of water. They attain a considerable speed during their flight, probably between twenty and thirty miles an hour. In the daytime these fish fly away from the ship; at night they fly at it, and sometimes enter a porthole.
The Bonito is a large fish often seen in tropical seas. This creature is capable of taking enormous jumps out of the water. It is said to feed upon flying-fish and to catch them during their flight in the air.
Before leaving the subject of marine vertebrata, mention must be made of the turtles which are sometimes visible in great numbers floating in the Mediterranean near the shore. These organisms are especially abundant off the Coast of Greece. Their carapace acts as a most efficient float.
Insects are frequently blown out to sea by gales of wind, and occasionally fall on ships. In the Red Sea we passed through a flight of locusts, a great number of which fell upon board. As a rule, insects are not common at sea. There is, however, a small white moth that flits over the surface of the ocean. This insect is common in the Arabian Sea. How these moths get there is a mystery. Some people think that they are evolved from grubs on ships. Their number would, however, seem to preclude this theory.
Great variety of bird-life is not usually seen during the voyage from England. On the banks of the Suez Canal an Egyptian vulture may sometimes be espied, while the marshy lakes in that region contain a variety of bird-life; among other forms flamingoes are conspicuous. In the open sea one now and again comes across a flock of migratory birds. While in mid-ocean birds are few and far between; with the exception of a few gannets, the atmosphere appears almost devoid of bird-life.
Near land gulls are numerous and follow the ship in considerable numbers. The movements of sea-gulls are extremely graceful. These beautiful creatures keep pace with the ship with ridiculous ease, now just skimming the water, now soaring high in the air; at one moment far behind the ship, at the next directly over head, flying round and round in circles. These birds seem able to fly for hours without tiring. A dozen flaps of the wing in a minute is more than sufficient to enable them to keep up with the boat, that is to say, to fly at the rate of about fifteen miles an hour. They are, however, able to attain a far greater velocity. It is difficult to estimate the greatest speed at which gulls can fly, for they probably rarely extend themselves. The writer’s observations would seem to indicate that gulls have no difficulty in flying, for a short distance at least, at the rate of forty miles an hour. This would seem to coincide with the results of other observers. The flight of birds is a most interesting subject, and one upon which our knowledge is at present very incomplete. For purposes of flight birds fall into two classes—those with heavy bodies and short rounded wings, and those with light bodies and large wings. The former move their wings very rapidly, and fly for a short distance with great velocity. Thus, driven partridges are said to travel at a speed of sixty miles an hour. This class of birds cannot fly far, and are not usually found at sea. The gull and the gannet belong to the other class, their wings being long and their bodies light. They are able to accomplish long journeys, often at great speed. The motion of their wings is always slow. In one experiment a swallow flew 160 miles in ninety minutes, or at the rate of 106 miles per hour. Gulls may be able to attain such a speed, but under ordinary circumstances they never do so. The writer has spent many hours watching these birds, and never has their pace approached this rate. Forty miles an hour would appear to be their limit. But they are never pushed, so may be capable of yet greater speed. Could anyone devise some experiment, whereby the velocity of flying birds could be accurately gauged, he would be a benefactor to science.
Gulls, like vultures, have excellent sight. If pieces of bread be thrown into the water, the gulls will quickly seize them, but they will not take the slightest notice of paper-balls similarly thrown to them. They appear to fly with eyes fixed upon the water. If a piece of bread be thrown from a moving ship into the sea the gulls which are ahead of the bread when it reaches the water will make no effort to pick it up, apparently not having seen it. On the other hand, one of the gulls behind the bread when it drops into the water will never fail to secure it.
The sea-gull is, perhaps, the most fascinating of all the interesting studies that present themselves to the naturalist during the voyage to England.
