Wanderers of ocean

 

Tour to Neocene

 

7. Wanderers of ocean

 

 

 

Times of greatness of Pacific ocean gradually pass: it is compressed from the west and the east by a ring of continents. America and Asia adjoin in the north, having formed a mountainous isthmus, Australia gradually moves to the north and already stands on equator by northern coast. Only Antarctica does not restrict Pacific ocean, being shifted to Indian ocean.
Climatic zones of Pacific ocean also have undergone some changes: Australia and New Guinea, as if a huge breakwater, deflect Southern Passat current in southern latitudes, having made the South Pacific warmer. The branch of Northern Passat current deflected by them has considerably warmed a coast of Asia. But the American coast are under the influence of cold waters, especially the coast of South America. Northern Pacific due to the Beringian isthmus is isolated from cold waters of Arctic ocean and there water is warmer, but waters of Southern Pacific leave much further to a pole, not carried away by Current of the Western Winds. Due to this Peruvian current became much stronger and colder, having affected a climate of the south of South America. But the centre of Pacific ocean has remained warm: from Atlantic warm current comes through the opened Panama strait.
In the alive world of Pacific ocean there were essential changes. Mass extinction has carried away to non-existence richest fauna of cetaceans that has enabled a plankton to breed in huge amounts. And the abundance of this forage has pushed survived inhabitants of ocean open spaces and also the “beginners” applying for a generous piece of plankton "pie" to a new way of evolution. As whales, filtering plankton in huge amounts, had become extinct, and other tetrapods, making it so well, has not appeared in the sea, the place of alive plankton trawls was occupied by fishes. And the sailerfish is the most widespread species of them. It is the typical inhabitant of a thickness of water with a high body of blue color, imperceptible from afar in ocean blue. The sailerfish is goog swimmer, but sometimes it prefers to travel at will of waves, if to be more exact - sea currents. Each spring shoals of these fishes go on feeding to coast of Antarctic Region. The sailerfish migrates by innumerable schools containing hundreds of individuals. Warm current from the equator, taking place near coast of Australia is the fine transport for them. Having got in the necessary stream of current, fishes turn from active swimmers to practically plankton creatures. They simply open huge pectoral fins as sails, and drift on current, occasionally stirring with tails lazy. This way they reach southern latitudes completely lost-free stocks of fat, run low in equatorial waters before it. In a way fishes do not eat - current is poorly by large zooplankton, but it’s richly in microscopic algae. The deep waters enriched with nitrogen and phosphorus, rising on a surface at underwater mountain ridges of Antarctic Region, stimulating breeding of phytoplankton and provide set of alive creatures with food.
Due to approaching to southern latitudes water becomes more opaque - the zooplankton starts to develop in it: thousands of crustaceans, jellyfishes, larvae and eggs of sea animals. It does not stop sailerfishes on their travel, but it enables fishes to begin to put on weight.
If the whale scoops crustaceans by portions, emerging on a surface of water, the sailerfish makes it by more perfect way, not interrupting in its way. Entering to congestion of a plankton, the fish opens the mouth. At the first sight at a fish it can seem, that this mouth does not represent anything special. But being opened, it becomes one of wonders of nature engineering idea: being repeatedly stretched, it turns to a huge trawl for an edible trifle. Branchial petals are covered with millions hairs of an epithelium, employees for food filtering. It seems, as if the fish has received a mouth intended for a creature much more greater in size - it looks so strange in this moment.
The school of fishes catches up with a congestion of a plankton, having constructed by slightly concave sickle. As if on command, they open mouths synchronously and start to move tails. To send the filtered plankton to a stomach, fishes simply cover operculums and sharply stir up them. Pectoral fins at a feed are pressed to sides of body: they only prevent to swim actively. Efficiency of a plankton feeding is very good: about half of congestion of plankton animals can settle in the fish stomaches after successful "trawling" of fish school. It is necessary for sailerfishes to put up weight: in cool southern waters they make breeding games. But while Antarctica is still far...
Having eaten plenty, fishes synchronously fold mouths, straighten fins and continue slow wandering to the cold south.
Movement of giant schools of large fishes does not remain unnoticed, and predators appear from depths. The bulldog shark rises from shallows of a continental shelf. The wide body shows that this fish is benthonic predator, but colouring of it is closer to colouring of pelagic fishes. A head of the bulldog shark is short and wide. The predator is easily kept swimming due to a large fat liver. This fish does not like to swim long time - it knows by experience, that catch will come to it itself. In rather turbid water on some distance there is one more shark of this species, behind it there are more and more of them. Sharks form as if a trail above a shelf. And they are waiting.
At last from a blue haze there is appearing a silhouette of a huge fish, near of it there is another one, and in front of sharks there is appearing literally alive wall of sailerfishes. Fishes are swimming, practically not turning aside, directly to sharks. Also there comes the moment when hungriest of predators is solved on an attack. It rushes on the small sailerfish, easily catches up with it and by a sting from below snatches out to all its interiors. Felt blood, other predators as if on command attack a school of sailerfishes. Jaws cut to pieces bodies, tear off tails and crush backbones. In water the huge head which completely has been bitten off from a body slowly sinks. It seems, that phlegmatic giants are doomed. Sailerfishes lose in arms to sharks: their tiny teeth also are adapted only to closing a mouth more closely. Their only ways of rescue are maneuverability and speed. From lazy passive swimmers at danger they instantly turn to the fast-moving creatures, capable to evade from any predator. Besides they have surprising way of protection.
The schooling way of life transforms fishes to world champions on synchronous swimming. And this feature sometimes rescues sailerfishes. Their school gathers speed, directs to a surface, and...
The surface of ocean of southern latitudes is quiet. But suddenly for a distance of hundreds meters from water thousands of huge fishes simultaneously fly up to two-meter height, are simultaneously turn aside, and simultaneously fall to a surface of water. This action makes a roar similar to explosion of several bombs at once. And the sea again calms down: second time this performance will not be repeated, at least, today.
The sound wave of improbable force literally guzzles sharks, forcing them to stop hunting and to go to the depths. And one of them obviously feels like badly: it convulsively pulls all body, and its colouring began appreciablly more pale than it is usual. And sailerfishes continue the swimming to coast of Antarctica with the minimal loss.
The Antarctic shelf is a place where deep current leaves on a surface and mixes up with rather warm water of equatorial current. And it stimulates development of life in this place. Water gets a greenish shade because of mass of a phytoplankton, and it is devoured with actively breeding zooplankton - microscopic crustaceans, jellyfishes, tiny little squids and pteropod molluscs in huge quantities. They swarm like clouds in water, painting it to reddish and brownish color to many hundreds meters. And there is a set of eaters for plentiful quantity of zooplankton.
Sailerfishes are not unique species fattened on ocean pastures of the south. At them there is plenty of competitors, and the most numerous of them is “the red robber”.
“The red robber” is the small black-eyed crustacean of the bright red color had replaced herring species in the ocean of Neocene. Large shoals of this crustacean form dense veils and catch all more or less big plankton organisms with the help of the legs covered with hairs. As well as the sailerfish, this crustacean can eat continuously, devastating waters of ocean. However it never will make it completely: there are fishes who willingly eat these crustaceans.
The strange big-nosed shadow appears from depths of ocean. It purposefully goes to school of "red robbers” turning at the surface of water. Crustaceans have found the dead bird going down stream, and now they try to snatch a more fatly piece. Water on a surface literally boils around of a bird body. The most impatient crustaceans jump out from water and fall on food from above. And the shadow meanwhile sneaks closer up to them. The sharp throw the shoal of crustaceans also follows. Long flat rostrum makes movement from below upwards, the whirlpool formed under it turns crustaceans, put out their orientation in the water. The huge mouth opens and sucks helplessly turned crustaceans in.
This hunter is the paddlefish ray, the descendant of a sawfish. Teeth on a well-known “saw” were reduced up to tiny spikes for a long time, and it has turned to the fine instrument for driving together tiny schooling creatures. The inferior mouth of a sawfish has turned in the beginning to sliding one, and then to the extensible net, capable to swallow at once hundreds of small food organisms fast and without problems. Small eyes on each side a flat snout look not so much in sides, as forward, helping to estimate density of crustacean shoal.
Usually paddlefish rays hunt, fast "cutting" lengthways through stretched shoal of crustaceans. Thus the flat snout allows them to stun a part of crustaceans, not giving them to swim out. These fishes are solitaries meeting only in a breeding season. Sometimes near large school of crustaceans some fishes of this species can be met. At this case it is possible to observe group hunting of paddlefish rays: fishes are turning around of crustacean school, having turned to them by a belly. White color of a fish belly frightens “red robbers”, forcing them to gather to a dense shoal. Here paddlefish rays also open trap mouths, picking up set of crustaceans.
But if the paddlefish ray is mostly the solitary species, other sea hunters are schooling fishes. Amazingly beautiful tunnymullets attack the “red robber” by the organized school. They are pressing crustaceans to a surface of water and are simultaneously thrown on them, forcing crustaceans to jump out to air highly. Sea birds, small yellow-headed divesparrows, use it. During flights to subantarctic islands they willingly catch “red robbers” together with a tunnymullets. Birds look for red stain at the sea surface, and direct to it, picking up crustaceans right in air. But even at all their diligence tunnymullets can not to have eaten all crustaceans, because they are not last part of a food chain.
Bulldog sharks use gifts of the Antarctic summer, trying to save up as much as possible fat for wintering at the sea bottom. Winter is hungry rather than cold season: during polar night the phytoplankton in the sea almost disappears, the amount of a zooplankton falls also schools of fishes go to warmer latitudes. But for now it is a lot of food and large-toothed predators keep their eyes open.
The school of tunnymullets approaches to a surface of water. These fishes are capable to gather huge speed, but now they do not hasten. Fishes are going to spawn, and this occupation does not suffer haste. The school of fishes is slowly turned on small depth. Suddenly from it the female ready to a spawning is separated, and rushes aside at big speed. Immediately two males direct behind her. They quickly catch up with her and squeeze female from sides. The female spawns a portion of eggs in water, and males fertilize eggs with soft roe, that’s why the whitish cloud blurs in water. Then fishes come back to school and are included in the common circulation again. Further pair of females escape out of school at once, but each of them is caught up with pair of males and in water two new clouds of eggs appear. And again the school continues to turn around. It is the necessary ritual, assisting to synchronize readiness for a spawning of fishes. And then as if the spring bursts: the school literally scatters to triplets of fishes, making water opaque because of egg clouds. Some fishes have not spawned - they while are young.
The school of fishes weakened after a spawning is gathering. They have executed the duty to future generations, and the destiny of eggs does not interest them any more. Tunnymullets swim slowly above a shallow, and after them from a bottom the silvery wide-headed shadow rises. It follows school some time, as if waiting, and then attacks promptly. And than one bluish large fish beats in predator’s mouth, powerlessly opening jaws wide. Having swallowed it, the shark rushes on tunnymullets once again. The weakened fishes are too sluggish, though another time they would not admit a shark to a distance of true throw. And the shark takes the tribute from other inhabitants of ocean, using the right of might.
Sailerfishes will spend breeding games in Antarctic waters too. But they keep in the high sea, not coming nearer to shallows. It protects fishes from an attack of bulldog sharks. Males become breeding colored, and females become more pale. Each male occupies a small area at a surface of water where it tries to involve the female, shining in beams of sun. To declare the right on individuality, from time to time the male jumps out of water and plops down the side, lifting fountains of splashes. When females approach to congestions of males, red-sided grooms start to utter a mansion breeding signals similar to a crash of the motor. Thus they open pectoral and abdominal fins, transforming them in similarity of a fan or a magnificent collar. When the female approaches close to the chosen male, it starts to be stirred up by all body, and then folds pectoral fins and presses itself to the female sideways and a stomach. Pair accepts position of "book". At this time cloacas of both fishes swell and also incorporate by apertures, and the male transfers to the female liquid roe. As against many other fishes, at the sailerfish there is an internal fertilization. Fries ripen a long time in ovaries of the female, but they are born already advanced and independent, and the death per cent of them is insignificant.
When summer comes to an end, and the sun above the Antarctic waters starts to set, fishes leave coast of this continent. Schools of sailerfishes search for a branch of current which will carry them away from Antarctica along the coast of South America in the central area of Pacific ocean where fishes will wait polar winter. There is not so much plankton, but there is a special place where fries of these fishes will be born; and there they will grow and develop the first year of life, preparing for wandering under sails to the southern seas.

Bestiary

“Red robber” (Gregariomyzis planctophagus)
Order: Myzida
Family: Mysidae

The pelagic swimming crustacean from myzid group (Myzida). Length of a body is up to 40 mm. It spends all life in the top layer of water (up to depth 80 - 100 meters, for a feed rises to a surface). It formes big shoals numbering up to 1200 crustaceans on 1 cubic meter of water, stretched on some hundreds meters. The species feeds by small zooplankton, being the food competitor of the sailerfish and occupying an ecological niche of the herring became extinct to a Neocene. Sometimes crustaceans of this species can eat dead fishes in a thickness of water. It has bright red colouring of the body, eyes are large and black. Legs of the crustacean are long and covered inside with the bristles, allowing to filter plankton. Animal filters plankton, moving forward an abdomen in its congestion; thus legs are formed so called "basket", catching edible organisms. Long mandibles of the crustacean survey "basket", pulling out and sending in a mouth got food organisms.

Bulldog shark (Brachyselache ginglymostoma)
Order: Orectolobiformes
Family: Orectolobidae

Picture by Alexander Smyslov

Pelagic shark, the descendant of the modern nurse shark (Ginglymostoma cirratum). The mouth is almost terminal (at the nurse shark there is an inferior one), it is remarkable by a short top jaw. After extinction of pelagic sharks this species which had descended from coastal sharks, had taken their place of an active predator of the top water layers. This shark lives in the top layer of open ocean up to depth of 50 meters, sometimes falling up to depth of 400 meters for hunting at ocean shelf.
Body is up to 5 meters long, almost cylindrical, slightly flattish, a tail stalk is quadrangular in section. The mouth is wide, a cut of a mouth comes for a vertical of an eye. Small eyes are located at sides of heads. Near corners of a mouth there is pair of short wattles. Unpaired fins are crescent, a tail fin is almost equal-lobed (as at a tuna). Pectoral fins are wide and short. Colouring of the body is silvery with a grey shade, the end of a back fin is black. Very big liver is rich in fat, this feature allows a fish to support floatage. The bulldog shark swims slowly, but pursues catch, making throws with speed up to 60 kms per hour. Eats fishes, cephalopods and large crustaceans.
The female gives rise once a year up to 10 large independent youngs (up to 60 cm long).

Tunnymullet (Thunnomugil cyanogaster)
Order: Mullets (Mugiliformes)
Family: Pelagomugilidae

Oceanic schooling fish up to 1,5 meters long, weighting up to 50 kg. It belongs to order Mugiliformes. A body is strong, brawny. A tail stalk is short and rigid, tail fin is crescent. The fish is capable to accelerate momentum over 60 kms per hour and to support it many hours in succession. The scales are very small, shipped in skin. There are two back fins: prickly and soft one. A prickly fin is peaked, high, with the big silvery spot serving for recognition of individuals of the species. Pectoral fins are strongly shifted up, at movement of a fish they play role of elevators and stabilizers. Abdominal fins are narrow, at navigation fold in a groove on a belly. Eyes are large, the cut of a mouth reaches a level of a first line of an eye. Mouth is toothless, jaws are firm, capable to crush a firm carapace of a crustacean. The back is black, a belly is metal shine blue, along a side a silvery strip passes. An iris of the eye is red. Males and females do not differ on colouring.
Fish eats crustaceans, cephalopods and small fishes. In congestions of crustaceans tunnymullet eats, sufficing catch in a motion, not changing a direction of movement. Hunting small fishes, it pursues and surrounds fish shoal.
Eggs are pelagic (one female lays up to 8 - 9 million), larvae eat phytoplankton.

Paddlefish ray (Nectopristis polyodonopsis)
Order: Sawfishes (Pristiformes)
Family: Nectopristidae

Gristly fish, the descendant of a bottom-dwelling sawfish (Pristis). It had evolved to a pelagic way of life after extinction of a significant amount of pelagic fishes species.
Length of a body is up to 5 meters from which about 40 % accounts for long flattish snout. Teeth on edges of a snout are reduced, the mouth has moved in a forward part of a head and has increased, the body began higher, than at an ancestor. The tail fin began higher, almost equal-lobed (the top lobe is little bit longer bottom one). Fish swims rather quickly, accelerates momentum up to 40 kms per hour. Colouring of the top side of a body is grey with dark mesh figure, the bottom side is white with numerous grey spots.
The solitary fish, less often it is meeting by groups on 2 - 5 fishes. The main food of this species consists of schooling plankton crustaceans. Fish surrounds shoal of crustaceans, floating around them, by impacts of a flat snout it "bunches" crustaceans to dense shoal and grasps their with widely opening mouth. In a dense congestion of a plankton fish is simply slowly swimming through the shoal, having opened a mouth widely. At edges of gill openings there are short corneous fibers, allowing to keep the filtered catch.
The live-bearing fish, gives rise up to 10 - to 12 fries everyone up to 30 cm in length. For fry bearing the fish approaches to coast: fries are fed with benthos organisms, later they go to a feed by pelagic crustaceans. Males keep far from a coast.

Sailerfish (Pelagopomus navigator)
Order: Percoid fishes (Perciformes)
Family: Centropomidae

Large pelagic fish (length is up to 2 meters, weight is up to 200 kg), eating small plankton. After disappearance of whalebone whales these fishes has occupied their ecological niche. Fish is fattened in subpolar waters of both poles, at moving through equatorial waters almost does not eat. Belongs to snook family (Centropomidae) of order Percoid fishes (Perciformes). Snooks are predatory fishes of warm coastal waters, some of them are capable even to live in fresh water. Due to this fact it is more probable, that some species of their will pass the crisis connected to plankton disappearance at the ocean, surviving in the rivers and mangrove thickets.
Body of this fish is high and flattish from sides, a back is dark-dark blue metal shining coloured, sides are blue, the bottom half of body is white. There are two back fins: prickly and soft. Unpaired fins are transparent, pectoral fins are whitely, external edge of them is blue. The structure of pectoral fins is remarkable: they are very wide and long: their length is up to 1 meter; being opened this fin forms almost a semicircle. Somactids of pectoral fins are very strong, their bases are strong and brawny. During active swimming pectoral fins are folded and laid along a body, their functions wide abdominal fins located almost on a throat carry out. A head is very big: it takes till 1/3 of general length of fish; large eyes are in the top part of head. Branchial arches are transformed into filtering device: branchial stamens cover only top half of arches where they are protected by numerous corneous bristles. On the bottom half of branchial arch there are only long epithelial bristles overlapping all gleam between branchial arches. The backlash between bristles is small, it allows to filter food objects (crustaceans, fish fry, jellyfishes etc.) larger than 3 mm by size. Till the feeding the mouth of fish is opened widely due to extensible ligaments. The school of sailerfishes at feeding is formed by "wall" and intercepts almost all congestion of small zooplankton. From time to time eating fishes close mouth, at this moment they swallow the plankton which has collected by filtering device. Fishes eat mostly spineless soft-bodied animals and avoid congestions of large crustaceans with firm shells.
The sailerfish swims slowly, during migrations it practically passes to plankton community: having opened wide pectoral fins, fish goes on current, as under sail; it migrates by big schools numbering up to 300 - 500 fishes.
In southern waters there is courtship. The male is colored brightly: on its sides dark cross strips appear, the mouth and operculums turn colored bright red. The female turns pale and its belly grows stout. At sailerfishes there is an internal fertilization: at the culmination moment of breeding games the male and the female nestle against each other by cloacae in position of “slightly opened book”. The female gives rise in equatorial waters up to 250 yoing fishes of 20 mm long. First time they live in colonies of gardnersalpa, eating algae and small plankton organisms. Growing up to length of 10 cm and more (at 1 year age), they go to the north together with adult fishes. Sexual maturity comes at length 50 cm (at 4-th year of life), and fish grows actively till 20 years.

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