32) MARINE TURTLES
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.
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