MORE ABOUT SEA-TURTLES

Earlier this year we ran a few articles about the nesting activities of sea-turtles up on the coast of northern Zululand in the iSimangaliso Wetland Park. The nesting season began again at the end of October. At present we are in the latter days of the nesting activities but are in the middle of hatching activity of the two species that nest on our beaches – the loggerhead and leatherback turtles. For over fifty years these activities have been closely monitored by successive teams of researchers.

The Turtle Survey, as it has been known for over 50 years was started in 1962 as a result of the uncontrolled slaughter of nesting animals, at the time, and a great deal of scientific research began because so little was known about the KZN population of these fascinating creatures. The KZN Turtle Survey is now the longest running sea-turtle research programme in the world.

Researchers wanted to know where the KZN turtles went to when they left our beaches, and the only means at their disposal was to fix a metal tag onto as many nesting females as possible. On these tags was engraved a series number and message promising a reward to the person who, on finding a tag, returned to the Oceanographic Research Institute in Durban. This gave researchers an insight into the movements of the loggerhead turtles, which moved up Africa as tag returns often came from coastal Kenya and Somalia. The leatherbacks remained a mystery as they are true ocean wanderers. Dead ones occasionally washed ashore on the west coast or were found in shark nets along the KZN coast.

With the events of 1994 came a relaxation of the strict embargo on many things. Scientific research was one of them. The first foreign researcher to interest himself in our sea-turtles was Professor Floriano Papi of Pisa University on Italy. He was an expert on the satellite tracking of animal migrations. Accordingly some loggerheads were caught as they returned to the sea after nesting and had a tiny radio transmitter glued to their backs. This transmitter would send a location signal to a satellite every time the turtle would break the surface to breathe. The results confirmed what we already knew – the loggerheads travelled up the east African coast and settled into feeding grounds along the Kenya, Somalian and Eritrean coasts.

Illustration 1: Professor Floriano Papi of Pisa University, applying the first satellite transmitter to a loggerhead, assisted here by Malcolm Burningham. We still had no idea where our leatherbacks were going to – for the simple reason that the leatherback is covered by a soft skin and it was impossible to glue a transmitter to it.

The nest season, however, we had a flexible harness to fit to a leatherback. It was not long before the results started to come in. And they were startling. Our transmitting female travelled 600 km out to sea where she she spent some time. Other marine biological research had revealed the presence of a jellyfish layer some 600 metres below the surface. The leatherback was diving to feed in this layer seeing as her natural food was jellyfish. Then she turned and headed south-west until just off Cape Agulhas she headed directly south, towards Antarctica, for nearly 500 km. Suddenly her wandering track took off east in a dead straight line and after some time the transmissions ceased. It is known that no animal track ever forms a straight line so the only answer was that our first satellite-transmitter-carrying leatherback had been picked up by a foreign fishing vessel and slaughtered.

In subsequent years, however, the satellite tagging programme was refined. It was taken over by the South African Department of Environment Affairs, Sea-fisheries section, and their scientists teamed up with Ezemvelo KZN Wildlife staff and researchers from the Nelson Mandela Metropolitan University in Port Elizabeth. Results showed that leatherback turtles that nested on the Zululand shores of KZN made their way around the Cape and headed up the west coast. Unfortunately, the batteries that powered the tiny transmitters would usually fail somewhere off Angola. The record, however, came from a transmission from near St Helena island.

Illustration 2: A mature leatherback female fitted with a flexible harness holding a satellite transmitter

Over the years a clearer picture of the extent of movement of our nesting sea-turtles was formed. The problem remains, however, that while we can offer them absolute protection in our coastal waters, we cannot protect them on the high seas.

We will continue our turtle story in next month’s newsletter

2 replies
  1. Mike Macfarlane
    Mike Macfarlane says:

    Can you give some indication as to how long the turtles eggs hatch after being laid. Also when is the most common time that the hatchlings come out ?

    Regards

    Mike Macfarlane

    Reply
  2. Rhino Club Team
    Rhino Club Team says:

    Hi Mike – loggerhead turtles eggs incubate for about 64 days, and leatherbacks about 72 days. So, loggerhead eggs laid at the start of the season – ie mid-October – would hatch about mid-December. Leatherbacks would start hatching at the end of December. January is a good month to go turtle watching as there is an overlap between nesting and hatching, so your chances of seeing some turtle activity are pretty good.

    Reply

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