Oceanic nekton

The ocean abounds with excellent swimmers who, in the words of the famous German nineteenth-century biologist Ernest Haeckel, “free to find their own way”. They can resist the strong current of water and to choose their own way, different from the animals of the plankton. The combination of these actively swimming animals E. Haeckel called the nekton, which means “floating”. Technically, the nekton are aquatic snakes, birds, and animals, but here we will talk only about the two groups of nektonic organisms — the fish and cephalopod molluscs.

Important nektonic animals adaptations to life in the water column of the ocean, according to Professor Yuri Aleev are maintaining the body in a suspended state, creating a driving force, reducing the resistance of the counter flow of water, control the movement of the body, as well as in the ability to disguise and protection.

All of these qualities to the limit pronounced among flying fish. When the ship is subtropical or tropical waters, flocks of silvery fish with dark blue fins suddenly appear in front of the bow and, describing a wide arc, rushing to the side of the ship, gleaming in the sun. Their long pectoral fins tremble slightly. It seems that the fish here-here again will be submerged, and they are all flying from crest to crest of a wave, put “pancake” rocks.

Before the flight, flying fish accelerates under water, tail working hard. The pectoral fins are thus pressed to the sides. Jumping to the surface, she dismisses them and continues to beat on the water bottom, the greater lobe of the caudal fin. Finally, reaching the speed limit, it detaches from water and flies over it like an arrow. The flight lasts 10 — 15 seconds, during which the fish manages to fly 150 to 200 meters. Flight altitude is usually minor, but not unknown cases where flying fish at night did drop to the deck (5 — 10 meters above waterline). Flight serves them protection from koripan, tuna, sailfish, barracudas and other predators.

There are many species of flying fish, but they never form large flocks and therefore not prominayutsya, despite its high palatability. Difficult and the method of their production. The fact that the bait of flying fish are not caught, and put them on the network there is no calculation. However, when a certain skill to catch such fish it is possible. To do this, the ship falls at night to drift, and overboard lowered brightest bulb. Immediately in the lighted circle, the different inhabitants of the sea, attracted to the light. Fit and flying fish. They swim slowly at the side, sometimes spreading like a fan the pectoral fins. But the slowness of their deceptive, at the slightest alarm fish short with a jerk popping out of the water and disappear in the dark.

For fishing use a tapered fine mesh net fitted to a heavy metal Hoop with a diameter of 60 — 80 centimeters. To the Hoop over three of the leash is attached a strong cord. The tackle is thrown vertically in front of the fish. Startled, she returned home and when luck is in the net. This method of fishing requires a high art in throwing a heavy tackle, but trained hunters usually brings a good catch.

Most of the salmon grows up and raise in the sea, and for spawning, it enters the river. Emerged from the eggs, the fry the first time live in fresh water and then migrate down to the sea and stay together as a single herd until puberty, when it again returned to “his” river for spawning.

In the North Pacific ocean fattened herds of salmon and Asian and American origin. For the purposes of the fishery is very important to know which herd it belongs caught fish. The fact that not all herds are equal in size and productivity and for each of them can only provide some fishing pressure. Set the value of the herd at the number of fish entering the river, and the largest spawning grounds, but how do you know where I came from fish caught on the high seas?

To solve this daunting task has been the graduate student of the Zoological Institute Academy of Sciences of the USSR, laureate of Lenin Komsomol prize Stanislav Konovalov. He applied for the differentiation of herds sockeye (red) original method, concurrently while researching parasites and the morphology of the fish scales. In the freshwater period of life of sockeye salmon infected with parasites of several species. They served as indicators to distinguish between herds. It turned out that for fish each herd has its own set of parasites. To identify which of the herd met the fishing vessel, it is enough to open the fish caught at sea to identify and count its parasites.

Fish of different herds differ slightly in their biology, with some fresh water juvenile lives longer, in others this period is less. Stay in the river and in the sea nahdet reflected in the structure of the scales. Detailed study of the microscopic structure of the scales, S. Konovalov radius of the freshwater zone and first summer of life at sea was able to differentiate all the same sockeye.

The combination of both methods allows to study the distribution of in the sea and migration of large commercial stocks and to correctly determine the pressure on each of them. The work of S. Konovalov was not only brilliantly defended as his thesis but also awarded the prize of Lenin Komsomol. Now a young scientist continues his research in the far East as Director of the Pacific Institute of fisheries and Oceanography.

Man invented the apparatus for movement in air and on land to develop a much greater speed than animals, but in the water the fastest are still fish. The speed record belongs to a swordfish, give her a few sailfish and Marlin. The pursuit of prey, they are accelerated to 120 — 130 kilometers per hour. The structure of these fish is a bright example of hydrodynamic perfection. Enough to say that their body has a streamline shape, it perfectly complies with the strict requirements of hydrodynamics applicable to fast moving objects.

All the path, sword fish, from the tip of the nasal bones projecting forward as rostrum supersonic airliner, narrow blades to large caudal fin, represents quick movement. Sharp sword, gradually thickening, slowly get into the head. Torpedovidnoj, rounded in the cross section of the body ends improbably thin, elegant stem of the tail. No unnecessary protruding parts.

The Marlin and sailfish unpaired dorsal and caudal fins are composed on the fly and drowned in special grooves. A small sickle-shaped pectoral fins pressed against the body, pelvic fins rudimentary or absent. At high speed the stabilizers serve two vertically arranged small extra fin on the tail stem and are hardly noticeable lateral keels at the base of the caudal fin.

Everything is geared to ensure that there is no turbulence, inhibiting the progress. Notched tail fin allows you to increase strength, driving the fish forward. Its long blade made out of the vortices and the layer of friction. But maneuverability hasn’t reduced. During steep turns begin to work the pectoral fins, the body support upright of the sliding grooves and podvorovoy dorsal fins.

Fast swimming consumes large amounts of energy, and the muscles of fish noticeably heats up. Just caught the spinning sword fish or related high-speed tuna seem hot to the touch, as warm-blooded animals.

Adaptation of a sword-fish and tuna to fast swimming has gone so far that these fish can’t stop. Otherwise they will suffocate. Their Gill covers are opened alternately together with the curves of the body, the mouth always half open, and on-the-go through it to the gills supplied with fresh water. Stationary fish can’t breathe, and the high level of all life processes require a large amount of oxygen.

All the sword-fish and tuna are predators, chasing their prey — fish and other cephalopods in the open ocean. Record the speed of the fish develops only in the pursuit of prey or in flight, and only at short distances, and cruise speed are quite high. So, one tuna tagged in the Bahamas, crossed the Atlantic ocean and 50 days was caught near Bergen. If we assume that it moves in a straight line, a distance of about 9 thousand kilometers was overcome with an average speed of 7.5 kilometres per hour. But he certainly wasn’t looking for the shortest route to re-take the hook.

The sword-fish are not of large size (up to 3 meters in length and 100 kilograms in weight), but at the point of attack at high speed it deals painful blows. In the stomachs of swordfish repeatedly found tuna and other fish, chopped in half, or other damages, caused by a sharp sword.

There are known many cases of collision, the swordfish with the courts and even active attacks on bots and boats. Thus, according to Sazonov, in 1962, the swordfish sank the Japanese fishing schooner. Caught in the net, she broke free and punched the wooden side of the ship. Had to take urgent measures to rescue the crew.

During world war II, one American mine-layers while patrolling off the Pacific coast of the USA was unexpectedly attacked by the swordfish, which struck the wooden hull of the ship. The hole began to receive water. Barely managed to patch the hole and tow the minelayer to base. Registered case when the swordfish struck the copper sheet covering the vessel (5 mm), the oak paneling and the piece of wood the thickness of 30 centimeters. Even modern steel ships does not always withstand the pressure of this rapid fish. Off the coast of England from the swordfish got a few holes minesweeper naval forces of great Britain Leopold.

In 1966, one American bomber In-52 in flight off the coast of Spain dropped a hydrogen bomb. In her search took part the deep-sea vehicle “Alvin”. At a depth of about 600 meters, he was attacked with a large sword-fish, which was stuck his sword in the groove of the casing.

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