Turtles date back to long before the Age of the Reptiles, when their ancestors shared the world with dinosaurs. Like other reptiles such as crocodiles, lizards and snakes, turtles are cold blooded and live only in the warmer parts of the world. Marine turtles have a flatter, lighter shell than do tortoises, and their front and rear flippers are used for swimming. The turtles that nest on South African beaches are the loggerhead and leatherback turtle.

TURTLE BREEDING

Turtles spend most of their lives at sea, but must return to land to lay their eggs. Turtles are often highly migratory - nesting beaches may be up to 3 000 km from their feeding grounds. Marine turtles mate in the waters off the nesting beach, after which the female comes ashore, usually in summer and at night:

* As the female emerges from the surf, she lifts her head and is alert for danger. Turtles are easily disturbed at this point.

* Once satisfied there is no danger, the female then uses her flippers to drag herself up the beach, well above the high-water mark. She may move around to find a suitable site for her nest, and then digs a hole for her body using her foreflippers to throw sand back.

* She then uses her rear flippers to carefully dig a smaller hole for her eggs, removing only about a cupful of sand at a time. When complete, this hole will be about 450mm deep, and shaped like a flask.

* Up to 120 soft-shelled, round, white eggs are then dropped in batches of one to four. Most sea turtle's eggs are about the size of a ping-pong ball. When all the eggs have been laid, the female then gently drops sand onto the eggs.

* After disguising the nest she returns, exhausted, to the sea.

LOGGERHEAD TURTLE

* A large marine turtle, with a shell up to 1 metre long and weighing up to 160 kg.

* Large and powerful head with strong jaws.

* One female travelled 2 640 km in 66 days with an average daily swim of 60 km.

* World population estimated at 200 000, but many populations are declining.

* Up to 500 females a year nest on beaches along the northern KwaZulu/Natal coast, where they are protected.

LEATHERBACK TURTLE

* A very large turtle, up to 2,5 metres in length and up to 910 kg in weight.

* Found throughout the world, and can withstand cold seas.

* One leatherback travelled 6 080 km in 10 months and there is a recorded dive of 1 200 metres.

* About 100 - 150 females nest annually between St Lucia and the Mozambique border.

HATCHING OF THE EGGS

After 55 - 65 days the turtle hatchlings use an egg tooth on the end of their beaks to cut their way out of the egg. When most of the baby turtles have emerged they scramble at the walls and roof of the egg chamber, dislodging the loose sand which falls amongst the hatchlings and eggs, gradually raising the floor of the chamber and so lifting the turtles out onto the beach, rather like a lift. The turtles will not emerge until after sunset, when they burst out and make a dash to the sea. At night the sea horizon is brighter over the ocean and this light guides the hatchlings to the water.

During the dash to the sea up to 12 % of the hatchlings may be attacked by ghost crabs. For the first few months of their life in the sea they are extremely vulnerable to predators. It is estimated that of every 1 000 that enter the sea, only 1 or 2 will reach maturity. Survivors spend up to three years drifting in the open sea, feeding on floating organisms such as small jelly fish. Following the ocean currents they later return to coastal waters where they feed on shellfish such as mussels. It is believed that nesting females return to the beaches where they hatched.

THREATS TO TURTLES

The seven species of marine turtles alive today are all declining in numbers. Turtles face a huge range of threats to their survival, from the moment the eggs are laid in the sand, through to adulthood. Apart from the threats posed by other creatures, marine turtles are increasingly threatened by the actions of people throughout the world. In some areas, the eggs of certain species are dug up and eaten, while adult turtles are killed for food. Other problems include destruction of nesting beaches, disturbance of the nesting females, and accidental catching and killing of turtles in fishing nets. In addition, turtles mistake plastic bags floating in the sea for jellyfish and eat them. This may choke them to death or prevent them from eating properly. An estimated 44% of leatherback turtles have plastic in their digestive systems.

CONSERVATION ACTION

Turtles need to be protected wherever they are found. Their conservation is particularly difficult because they have such varied habits and large ranges.

* Nesting beaches must be protected against development and human disturbance.

* Trade in turtles must be effectively controlled.

* Plastic pollution must be reduced.

* The Natal Parks Board/KwaZulu Dept. Nature Conservation programme has been in operation for 30 years on the Northern Zululand coast, with dramatic results. Leatherback numbers have increased from 5 females in 1966, to over 150 during 1993; loggerheads from less than 200 to 500 during the 30th year of protection.

WHAT CAN YOU DO?

* Pick up litter, especially plastic items such as supermarket bags, which you find on beaches or along rivers.

* Do not buy products made from turtles.

* Avoid disturbing turtles if you find them on the beach. * Do not drive vehicles on the beach.

* Report injured turtles to the KwaZulu Dept. Nature Conservation, Natal Parks Board or ORI/Sea World.

FURTHER READING

SEA TURTLES - A GUIDE. G.R. Hughes. Natal Parks Board. 1989.

THE SOUTH AFRICAN TORTOISE BOOK. R. Boycott and O. Bourquin. Southern Books, Johannesburg, 1988.

USEFUL ADDRESSES

Natal Parks Board. P O Box 662, Pietermaritzburg, 3200. Tel. 0331-471961.

ORI/Sea World. P O Box 10712, Marine Parade, 4056. Tel. 031-373 536.

KwaZulu Dept. Nature Conservation. P/Bag X98, Ulundi, 3838. Tel. 0358-700552.

LINKS

Turtle Trax - A Page Devoted to Marine Turtles