Under the Sea Wind

by Rachel Carson

  Book

  2

  The Gull’s Way

  6

  Migrants of the Spring Sea

  BETWEEN THE CHESAPEAKE CAPES and the elbow of Cape Cod the place where the continent ends and the true sea begins lies from fifty to one hundred miles from the tide lines. It is not the distance from shore, but the depth, that marks the transition to the true sea; for wherever the gently sloping sea bottom feels the weight of a hundred fathoms of water above it, suddenly it begins to fall away in escarpments and steep palisades, descending abruptly from twilight into darkness.

  In the blue haze of the continent’s edge the mackerel tribes lie in torpor during the four coldest months of winter, resting from the eight months of strenuous life in the upper waters. On the threshold of the deep sea they live on the fat stored up from a summer’s rich feeding, and toward the end of their winter’s sleep their bodies begin to grow heavy with spawn.

  In the month of April the mackerel are roused from their sleep as they lie at the edge of the continental shelf, off the Capes of Virginia. Perhaps the currents that drift down to bathe the resting places of the mackerel stir in the fish some dim perception of the progress of the ocean’s seasons—the old, unchanging cycle of the sea. For weeks now the cold, heavy surface water—the winter water—has been sinking, slipping under and displacing the warmer bottom water. The warm water is rising, carrying into the surface rich loads of phosphates and nitrates from the bottom. Spring sun and fertile water are wakening the dormant plants to a burst of activity, of growth and multiplication. Spring comes to the land with pale, green shoots and swelling buds; it brings to the sea a great increase in the number of simple, one-celled plants of microscopic size, the diatoms. Perhaps the currents bring down to the mackerel some awareness of the flourishing vegetation of the upper waters, of the rich pasturage for hordes of crustaceans that browse in the diatom meadows and in their turn fill the water with clouds of their goblin-headed young. Soon fishes of many kinds will be moving through the spring sea, to feed on the teeming life of the surface and to bring forth their own young.

  Perhaps, also, the currents moving over the place where the mackerel lie carry a message of the inpouring of fresh water as ice and snow dissolve in floods to rush down the coastal rivers to the sea, diminishing ever so slightly its bitter saltiness and attracting the spawn-laden fishes by the lesser density. But however the feeling of awakening spring comes to the dormant fishes, the mackerel stir in swift response. Their caravans begin to form and to move through the dim-lit water, and by thousands and hundreds of thousands they set out for the upper sea.

  About a hundred miles beyond the place where the mackerel winter, the sea rises out of the deep, dark bed of the open Atlantic and begins its own climb up over the muddy sides of the continental slope. In utter blackness and stillness the sea climbs those hundred miles, rising from depths of a mile or more until black begins to fade to purple, and purple to deep blue, and blue to azure.

  At one hundred fathoms the sea rolls over a sharp edge—the rim of the bowl formed by the foundations of the continent—and starts up the gentler acclivity of the continental shelf. Over the shelving edge of the continent, the sea contains for the first time roving herds of fishes that browse over the fertile undersea plains, for in the deep abyss there are only small, lean fishes hunting singly or in small bands for the sparse food. But here the fishes have rich pasturage— meadows of plantlike hydroids and moss animals, clams and cockles that lie passive in the sand; prawns and crabs that start up and dart away before the rooting snout of a fish, like a rabbit before a hound.

  Now small, gasoline-engined fishing boats move over the sea and here and there the water pours through the meshes of miles of gill-net webbing suspended from floats or resists the drag of otter trawls over the sandy floor beneath. And now for the first time the gulls’ white wings are patterned in numbers on the sky above, for the gulls—except the kittiwakes—hug the fringes of the sea, feeling uneasy on the open ocean.

  As the sea comes in over the continental shelf it meets a series of shoals that run parallel to the coast. In the fifty to one hundred miles to tidewater the sea must hurdle each of these shoals or chains of shoals, climbing up the sides of the hills from the surrounding valleys to shelly plateaus a mile or so wide, then on the shoreward side descending again into the deeper shadows of another valley. The plateaus are more fertile than the valleys in the thousand-odd kinds of back-boneless animals that fishes live on, and so more and larger fish herds browse on them. Often the water above the shoals is especially rich in the moving clouds of small plants and animals of many different kinds that drift with the currents or swim feebly about in search of food—the wanderers or plankton of the sea.

  The mackerel do not follow the road over the hills and valleys of the sea’s floor as they leave their wintering grounds and turn shoreward. Instead, as though in eagerness to reach at once the sun-lit upper water, they climb steeply the hundred-fathom ascent to the surface. After four months in the gloom of deep water the mackerel move in excitement through the bright waters of the surface layers. They thrust their snouts out of the water as they swim and behold once more the gray expanse of sea cupped in the paleness of arching sky.

  Where the mackerel come to the surface there is no sign by which to distinguish the great sea out of which the sun rises from the lesser sea into which it sets; but without hesitation the schools turn from the deep-blue saline water of the open sea and move toward the coastal waters, paled to greenness by the fresh inpouring of the rivers and bays. The place they seek is a great, irregular patch of water that runs from south by west to north by east, from the Chesapeake Capes to southward of Nantucket. In some places it is only twenty miles from shore, in others fifty or more— the spawning grounds in which, from ancient times, the Atlantic mackerel have shed their eggs.

  Throughout all the latter part of April mackerel are rising from off the Virginia Capes and hurrying shoreward. There is a stir of excitement in the sea as the spring migration begins. Some of the schools are small; some are as much as a mile wide and several miles long. By day the sea birds watch them rolling landward like dark clouds across the green of the sea; but at night they pour through the water like molten metal, as by their movements they disturb the myriad luminescent animals of the plankton.

  The mackerel are voiceless and they make no sound; yet their passage creates a heavy disturbance in the water, so that schools of launce and anchovies must feel the vibrations of an approaching school a long way off and hurry in apprehension through the green distances of the sea; and it may be that the stir of their passage is felt on the shoals below—by the prawns and crabs that pick their way among the corals, by the starfish creeping over the rocks, by the sly hermit crabs, and by the pale flowers of the sea anemone.

  As the mackerel hurry shoreward they swim in tier above tier. Throughout those weeks when the fish are rolling in from the open sea the scattered shoals between the edge of the continent and the shore are often darkened as the earth was once dimmed by the passing of another living cloud—the flights of the passenger pigeons.

  In time the shoreward-running mackerel reach the inshore waters, where they ease their bodies of their burden of eggs and milt. They leave in their wake a cloud of transparent spheres of infinitesimal size, a vast, sprawling river of life, the sea’s counterpart of the river of stars that flows through the sky as the Milky Way. There are known to be hundreds of millions of eggs to the square mile, billions in an area a fishing vessel could cruise over in an hour, hundreds of trillions in the whole spawning area.

  After spawning, the mackerel turn toward the rich feeding grounds that lie to seaward of New England. Now the fish are bent only on reaching the waters they knew of old, where the small crustaceans called Calanus move in red clouds through the water. The sea will care for their young, as it cares for the young of all other fishes, and of oysters and crabs and starfish, of worms and jellyfish and barnacles.

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  Birth of a Mackerel

  SO IT CAME ABOUT that Scomber, the mackerel, was born in the surface waters of the open sea, seventy miles south by east from the western tip of Long Island. He came into being as a tiny globule no larger than a poppy seed, drifting in the surface layers of pale-green water. The globule carried an amber droplet of oil that served to keep it afloat and it carried also a gray particle of living matter so small that it could have been picked up on the point of a needle. In time this particle was to become Scomber, the mackerel, a powerful fish, streamlined after the manner of his kind, and a rover of the seas.

  The parents of Scomber were fish of the last big wave of mackerel migration that came in from the edge of the continental shelf in May, heavy with spawn and driving rapidly shoreward. On the fourth evening of their journey, in a flooding current straining to landward, the eggs and milt had begun to flow from their bodies into the sea. Somewhere among the forty or fifty thousand eggs that were shed by one of the female fish was the egg that was to become Scomber.

  There could be scarcely a stranger place in the world in which to begin life than this universe of sky and water, peopled by strange creatures and governed by wind and sun and ocean currents. It was a place of silence, except when the wind went whispering or blustering over the vast sheet of water, or when sea gulls came down the wind with their high, wild mewing, or when whales broke the surface, expelled the long-held breath, and rolled again into the sea.

  The mackerel schools hurried on into the north and east, their journey scarcely interrupted by the act of spawning. As the sea birds were finding their resting places for the night on the dark water plains, swarms of small and curiously formed animals stole into the surface waters from hills and valleys lying in darkness far below. The night sea belonged to the plankton, to the diminutive worms and the baby crabs, the glassy, big-eyed shrimp, the young barnacles and mussels, the throbbing bells of the jellyfish, and all the other small fry of the sea that shun the light.

  It was indeed a strange world in which to set adrift anything so fragile as a mackerel egg. It was filled with small hunters, each of which must live at the expense of its neighbors, plant and animal. The eggs of the mackerel were jostled by the newly hatched young of earlier spawning fishes and of shellfish, crustaceans, and worms. The larvae, some of them only a few hours old, were swimming alone in the sea, busily seeking their food. Some snatched out of the water with pincered claws anything small enough to be overpowered and swallowed; others seized any prey less swift and agile than themselves in biting jaws or sucked into cilium-studded mouths the drifting green or golden cells of the diatoms.

  The sea was filled, too, with larger hunters than the microscopic larvae. Within an hour after the parent mackerel had gone away, a horde of comb jellies rose to the surface of the sea. The comb jellies, or ctenophores, looked like large gooseberries, and they swam by the beating of plates of fused hairs or cilia, set in eight bands down the sides of the transparent bodies. Their substance was scarcely more than that of sea water, yet each of them ate many times its own bulk of solid food in a day. Now they were rising slowly toward the surface, where the millions of new-spawned mackerel eggs drifted free in the upper layers of the sea. They twirled slowly back and forth on the long axes of their bodies as they came, flashing a cold, phosphorescent fire. Throughout the night the ctenophores flicked the waters with their deadly tentacles, each a slim, elastic thread twenty times the length of the body when extended. And as they turned and twirled and flashed frosty green lights in the black water, jostling one another in their greed, the drifting mackerel eggs were swept up in the silken meshes of the tentacles and carried by swift contraction to the waiting mouths.

  Often during this first night of Scomber’s existence the cold, smooth body of a ctenophore collided with him or a searching tentacle missed by a fraction of an inch the floating sphere in which the speck of protoplasm had already divided into eight parts, thus beginning the development by which a single fertile cell would swiftly be transformed into an embryo fish.

  Of the millions of mackerel eggs drifting alongside the one that was to produce Scomber, thousands went no farther than the first stages of the journey into life until they were seized and eaten by the comb jellies, to be speedily converted into the watery tissue of their foe and in this reincarnation to roam the sea, preying on their own kind.

  Throughout the night, while the sea lay under a windless sky, the decimation of the mackerel eggs continued. Shortly before dawn the water began to stir to a breeze from the east and in an hour was rolling heavily under a wind that blew steadily to the south and west. At the first ruffling of the surface calm the comb jellies began to sink into deep water. Even in these simple creatures, which consist of little more than two layers of cells, one inside the other, there exists the counterpart of an instinct of self-preservation, causing them in some way to sense the threat of destruction which rough water holds for so fragile a body.

  In the first night of their existence more than ten out of every hundred mackerel eggs either had been eaten by the comb jellies or, from some inherent weakness, had died after the first few divisions of the cell.

  Now, the rising up of a strong wind blowing to southward brought fresh dangers to the mackerel eggs, left for the time being with few enemies in the surface waters about them. The upper layers of the sea streamed in the direction urged upon them by the wind. The drifting spheres moved south and west with the current, for the eggs of all sea creatures are carried helplessly wherever the sea takes them. It happened that the southwest drift of the water was carrying the mackerel eggs away from the normal nursery grounds of their kind into waters where food for young fish was scarce and hungry predators abundant. As a result of this mischance fewer than one egg in every thousand was to complete its development.

  On the second day, as the cells within the golden globules of the eggs multiplied by countless divisions, and the shieldlike forms of embryo fish began to take shape above the yolk spheres, hordes of a new enemy came roving through the drifting plankton. The glassworms were transparent and slender creatures that cleaved the water like arrows, darting in all directions to seize fish eggs, copepods, and even others of their own kind. With their fierce heads and toothed jaws they were terrible as dragons to the smaller beings of the plankton, although as men measure they were less than a quarter of an inch long.

  The floating mackerel eggs were scattered and buffeted by the dartings and rushes of the glassworms, and when the driftings of current and tide carried them away to other waters a heavy toll of the mackerel had been taken as food.

  Again the egg that contained the embryonic Scomber had drifted unscathed while all about him other eggs had been seized and eaten. Under the warm May sun the new young cells of the egg were stirred to furious activity—growing, dividing, differentiating into cell layers and tissues and organs. After two nights and two days of life, the threadlike body of a fish was taking form within the egg, curled halfway around the globe of yolk that gave it food. Already a thin ridge down the mid-line showed where a stiffening rod of cartilage—forerunner of a backbone—was forming; a large bulge at the forward end showed the place of the head, and on it two smaller outpushings marked the future eyes of Scomber. On the third day a dozen V-shaped plates of muscle were marked out on either side of the backbone; the lobes of the brain showed through the still-transparent tissues of the head; the ear sacs appeared; the eyes neared completion and showed dark through the egg wall, peering sightlessly into the surrounding world of the sea. As the sky lightened preparatory to the fifth rising of the sun a thin-walled sac beneath the head—crimson tinted from the fluid it contained—quivered, throbbed, and began the steady pulsation that would continue as long as there was life within the body of Scomber.

  Throughout that day development proceeded at a furious pace, as though in haste to make ready for the hatching that was soon to come. On the lengthening tail a thin flange of tissue appeared—the fin ridge
from which a series of tail finlets, like a row of flags stiff in the wind, was later to be formed. The sides of an open groove that traversed the belly of the little fish, beneath and protected by the plate of more than seventy muscle segments, grew steadily downward and in midafternoon closed to form the alimentary canal. Above the pulsating heart the mouth cavity deepened, but it was still far short of reaching the canal.

  Throughout all this time the surface currents of the sea were pouring steadily to the southwest, driven by the wind and carrying with them the clouds of plankton. During the six days since the spawning of the mackerel the toll of the ocean’s predators had continued without abatement, so that already more than half of the eggs had been eaten or had died in development.

  It was the nights that had seen the greatest destruction. They had been dark nights with the sea lying calm under a wide sky. On those nights the little stars of the plankton had rivaled in number and brilliance the constellations of the sky. From underlying depths the hordes of comb jellies and glassworms, copepods and shrimps, medusae of jellyfish, and translucent winged snails had risen into the upper layers to glitter in the dark water.

  When the first dilution of blackness came in the east, warning of the dawn into which the revolving earth was carrying them, strange processions began to hurry down through the water as the animals of the plankton fled from the sun that had not yet risen. Only a few of these small creatures could endure the surface waters by day except when clouds deflected the fierce lances of the sun.

  In time Scomber and the other baby mackerel would join the hurrying caravans that moved down into deep green water by day and pressed upward again as the earth swung once more into darkness. Now, while still confined within the egg, the embryonic mackerel had no power of independent motion, for the eggs remained in water of a density equal to their own and were carried horizontally in their own stratum of the sea.