Marine Turtles in KwaZulu Natal - Biology

Nesting

Both loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea) turtles nest during the summer months (October to March), venturing ashore at night to dig egg chambers in the cool beach sands. They prefer medium to coarse-grained sandy beaches that are backed by high dunes with well-developed primary vegetated dunes.
Steep beach faces make it easier for loggerheads to swim through the surf over low-lying rock ledges. The females emerge from the surf and rest in the wash zone on the beach. From here they assess the beach for any danger, and then proceed up the beach to well above the high water mark.

Egg Laying
Having found a suitable site at the vegetation edge, the female commences nesting by excavating a body pit with her fore flippers, and continues until the top of her carapace is roughly level with the surrounding sand.

She then digs an egg cavity with her hind flippers. The egg pit is a flask-shaped hole about 50-80 centimetres deep. A normal clutch constitutes 100-120 soft, white-shelled eggs, which are deposited into this hole. When all of the eggs have been laid, the female fills the hole with sand, and then kneads and presses the surface until the sand is packed hard.

Once this is done, she disguises the nest by throwing sand with her fore flippers over the nesting area. Satisfied that her nest is safe and not easily recognisable, she returns to the sea. Leatherbacks can return to lay eggs up to 7 times in a single season, while loggerheads return up to 4 times.

Hatching
Hatching takes place around February each year. Both loggerhead and leatherback turtle eggs take between 55 and 65 days to incubate. Once ready to emerge, the hatchlings cut their way out of the egg with a special egg tooth at the end of their beaks.

After the bulk of the eggs have hatched, the hatchlings start digging at the sides of the nest, this causes it to collapse, filling the hole, and allowing the hatchlings to push and climb their way through the sand to the surface. If the hatchlings reach the surface during the heat of the day they will not move until the temperature of the surface sand drops.

They will normally rest until nightfall before they emerge and sprint down to the sea. Hatchlings are guided towards the waters edge by the lighter sea horizon. During this run to the water's edge about 4% are taken by ghost crabs or other predators.

Life at Sea
Once clear of the beach, the hatchlings go into a swimming 'frenzy' that lasts for a few days. Many enter the offshore Agulhas Current and are subsequently swept down the east and south coasts of South Africa as far as Cape Agulhas.

Some even carry further on and venture out into the Atlantic Ocean. However, most are swept back into the Southern Indian Ocean - where they spend at least 3 years swimming and drifting in the open sea. It is during these first few years that predation is extremely high and it is estimated that only one to two hatchlings out of every 1000 that enters the sea will live to reach maturity.

During this phase the young sea turtles predominantly feed on blue bottles, jellyfish and storm snails that drift on the surface. Following the currents, the loggerheads gradually move back closer to the coasts and good feeding grounds.

Here they gradually change their diets and begin feeding on a number of sea organisms that inhabit reefs - such as sea urchins, mussels and crabs. Leatherbacks remain in the open ocean, eat an exclusive diet of jellyfish and only enter coastal waters to breed. Females reach nesting maturity between 12 and 20 years, when they return to the beaches on which they hatched, to restart the life cycle.
Leatherback turtle (<i>Dermochelys coriacea</i>) laying eggs on the beach. / ©: WWF-Canon / Martin HARVEY
Leatherback turtle (Dermochelys coriacea) laying eggs on the beach.
© WWF-Canon / Martin HARVEY
Leatherback turtle (<i>Dermochelys coriacea</i>) hatchlings coming out of eggs. / ©: WWF-Canon / Roger LeGUEN
Leatherback turtle (Dermochelys coriacea) hatchlings coming out of eggs.
© WWF-Canon / Roger LeGUEN

..only one to two hatchlings out of every 1000 that enters the sea will live to reach maturity..

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