Sea-Turtle Hatching Time

The sea-turtle hatching season is now a thing of the past until next year. In late October this year, however, gravid females will again make their appearances on the beaches north of Cape Vidal in the iSimangaliso Wetland Park, and the ancient ritual of nesting will begin all over again. This coming season’s hatchlings will begin to make their appearances at about Christmas or just in the New Year, and their epic journey will begin. Only two of the five species of sea-turtles nest on the Zululand beaches – the sturdy Loggerhead, and the massive Leatherback. The other species, although occasional visitors to our waters, very rarely nest here. These are the olive ridley turtle, the green turtle, and the hawksbill turtle.

A nesting female sea-turtle typically emerges at night, often on a rising tide. Loggerhead turtles, being cased in a sturdy carapace, can come ashore where it pleases them, as they can crawl across the rocks with impunity. Leatherbacks, however, are different in that their massive carapace is encased in a soft, leathery skin, so they have to use sandy beaches only, avoiding rocks which would shred the belly skin.

The female crawls up the beach, crossing the high tide line, until she encounters an obstruction such as a steep dune or vegetation. There, she systematically excavates a body depression using her fore and hind flippers. Once she has done this she begins to dig the nest cavity, using her hind flippers only. Left, dig, scoop, lift, flick; right, dig, scoop, lift, flick… She digs until her probing rear flipper no longer encounters any sand – the nest cavity is about 40cm deep in the case of the loggerhead, and about 60cm for the leatherback. Then she lays about 100 – 120 eggs. loggerhead eggs are about the size of ping-pong ball, while a leatherback egg is about the size of a billiard ball.

About two months later there is a great stirring in the egg chamber deep under the sand as hatchling sea-turtles begin their arduous scramble to the surface of the beach. Remember, the eggs were buried deep down by the female, and in some instances wind-blown sand has piled even more sand over the nest. The hatchling turtles emerge from their eggs in the tightly packed confines of the nest, in pitch darkness. They immediately begin to scratch away at the roof of the egg-chamber, trampling the rubbery egg-shells down in the process. As more and more hatchlings emerge from the eggs, the wriggling mass of little turtles literally bring the roof down as they claw away at the sand above them and trample it below them.

In effect the egg-chamber then begins to move upwards like a lift. As they near the surface they become aware of the surface temperature – if it is hot, the mass of hatchlings cease their scrabbling and wait for the sand to cool. This is an amazing and instinctive reaction, for if the sand is hot, it means that the sun is still up on the surface. For tiny creatures like the hatchling turtles to emerge onto the sun-baked beach would mean a rapid and agonising death. And so…they wait until the sand begins to cool. Then they resume their scrabbling, eventually clawing their way individually through a few remaining centimetres of loose, warm sand and out into the protective blanket of night.

Darkness also shields them from the eager eyes of predators – to a point, for out on the sands, between the nest and the relative safety of the sea are literally thousands of ghost crabs. And a fully adult ghost crab can easily take a turtle hatchling, dragging the struggling little creature into its burrow where it consumes it at leisure.

The hatchlings, however, are  unaware of this hazard. They unerringly orientate themselves as they emerge from the sand, and begin the trek to the sea, their tiny flippers gaining in strength and mobility as they move down the beach in a pattering, struggling mass. Soon the first tongues of water begin to wash around them, and for the first time they enter their true world, washed hither and thither by the incoming waves. Without pause, the tiny creatures head through the surf and out to sea, heading for the great Agulhas Current many kilometres away over the horizon.

Their journey of life has begun and it is estimated that a mere one in a thousand will survive to maturity and return to same beaches to nest. Fish and sea-birds take a great toll of the hatchlings. Each one carries the remains of the yolk within its stomach cavity and this gives them enough nourishment for about two weeks. In this time they begin feeding on floating marine creatures like jellyfish.

Once in the Agulhas Current they are carried southward, sweeping towards Antarctica off the Cape, in the massive south Indian Ocean gyre, which eventually carries them up towards the Equator west of Australia, curving westwards and down in a southerly direction way off-shore of Africa and thus bringing them back to the beaches of their beginning some 15 to 20 years later.

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