The turtles of South Africa : Five species of turtle have been recorded in South African waters. The olive ridley turtle – Lepidochelys olivacia – is the most rare and is hardly ever encountered. Each species of turtle specialises in feeding on different prey, thus they ensure that they do not compete with each other for food and space. Turtles rely on air from the surface, but are accomplished freedivers. Remaining submerged for long periods and spending most of their life at sea, only the females will leave the ocean to nest on sandy beaches – seemingly the same sites they hatched from.
As with crocodiles, the temperature of the eggs dictates the sex of hatchlings 20-24 degrees Celsius produces males, while 29 degrees Celsius or more results in females. Clutches laid in mid season will produce both sexes.
Turtles are endangered world-wide and unfortunately, it is the nesting females, that are most at risk when they come ashore to lay eggs. Turtle meat and eggs are still eaten in some countries, gill nets, pollution, human ignorance and impact on breeding sites are all major threats to their survival. Turtles of South Africa :
LEATHERBACK TURTLE – Dermochelys coriacea.
Identification: The largest of all sea turtles. Leatherbacks can attain a mass of over 900kg and are easily recognised by the pliable, leather-like shell (up to 2.5m in length) with it’s 7 distinct lateral ridges. The body is dark, blue-grey in colour and mottled. The forelimbs are very large and prominent.
Biology: Female leatherback turtles come ashore at night on the high tide and in one breeding season, may lay up to 1000 eggs in batches of 100-200 at intervals of 9-10 days. The juveniles (only 50-60mm in length) then hatch after 70 days and head out to sea where as few as one in a thousand may reach sexual maturity. The female then returns every 3-5 years to breed again. Leatherbacks grow rapidly, feeding almost exclusively on vast numbers of jellyfish. They reach sexual maturity after only 4-5 years (12-15 years for other turtles).
Behaviour: Leatherbacks turtles travel the ocean currents in search of their prey and may dive to over 100m and remain submerged for up to 35 minutes. Found offshore around the whole coast, they breed in Northern KwaZulu Natal between November and January. In 1966 only 5 leatherbacks nested on the Zululand coast. Thanks to conservation efforts the average number of nesting leatherbacks has now risen to more than 90 – an encouraging recovery although their status still remains vulnerable. Leatherback turtles often mistake plastic bags for jellyfish and nesting females are still taken in some areas of Mozambique.
LOGGERHEAD TURTLE – Caretta caretta.
Identification: The head of the loggerhead is large and square. The shell is dark to yellow-brown and tapers to the rear with a row of five large plates on either side of the central plates. The shell plates on the loggerhead turtle do not overlap. Each limb has two claws and the bill is slightly hooked.
Biology: The breeding habits of the loggerhead are much the same as those of the leatherback. The females come ashore and lay up to 500 eggs at 15 day intervals. The juveniles then hatch after 60-70 days and head out to sea where they spend their early years drifting in the Agulhas current. Sexual maturity is reached at an estimated age of 12-15 years.
Behaviour: Loggerheads tend to keep more inshore, hunting around reefs and rocky estuaries. They use their strong jaws to crush prey which includes, molluscs, crabs, crayfish and sea urchins. Like the leatherback turtle they nest on the beaches of Northern KwaZulu Natal from November to January – see migration calendar. Since the early 1960s the population has increased from under 100 to over 500 nesting annually in the Maputaland Marine Reserve.
Identification: Like the loggerhead, the shells plates do not overlap. However, there are only four plates either side of the central row – the loggerhead has five. Females are usually darker than males the shell appearing almost tie-dyed in rich browns and ochres. The forelimbs have a single claw each and the bill is not hooked.
Biology and behaviour: Green turtles are resident in Southern Africa however, they do not nest on our shores. The nearest breeding grounds are on the islands of Europa and Tromelin in the Mozambique channel. The females lay only 600 eggs each season in batches of 150 every 12 days. Adults feed almost exclusively on algae and marine plants often entering estuaries to do so. Green turtles are under threat from hunting and egg collection.
HAWKSBILL TURTLE – Eretmochelys imbricata.
Identification: A relatively small turtle. The shell has thick overlapping plates, with twelve marginals on each side, those at the rear form a serrated edge and provide one of the best means for identification. The forelimbs have two claws and the bill is noticeably hooked.
Biology and behaviour: Hawksbill turtles breed in Madagascar and Mauritius. They occur only as a visitor to our coast. They feed on corals, sponges and urchins using their hooked bills to prise them from the bottom. Many thousands have been slaughtered in the past to provide the ‘tortoiseshell’ used for fashion accessories and decorative inlays.