In a joint venture between Ezemvelo KZN Wildlife (EKZNW), The Nelson Mandela Metropolitan University in Port Elizabeth (NMMU) and Marine and Coastal Management, three Leatherback turtles were recently attached with satellite transmitters and are currently being monitored as they make their way towards the Cape.
This is the fourth year that this project has been running, and the data that is collected as a result of it has been invaluable to Leatherback research says EKZNW media manager Jeff Gaisford. While information on Loggerhead turtle migratory patterns is fairly well known (due to the fact that they are a predominantly inshore species), less is known about where Southern African Leatherbacks go once they leave their nesting beaches in Northern Kwazulu-Natal. “The Leatherback is a true pelagic animal, they feed on jellyfish, which are available throughout the oceans and they travel huge distances. They go from our beaches, quite a long way offshore probably into the Agulhas current and then follow the 100 km offshore contour round the Cape and up the west coast. Data that we collected from the last three years shows that they definitely go up as far as Angola, but we don’t know where they go from there. Do they continue up the West Coast or do they in fact cross the Atlantic?”
In an attempt to answer these questions, a project group lead by Dr Ronel Nel from NMMU and Marine and Coastal Management’s Mike Myers spent a week at the end of January, combing the 200 km stretch of beach making up the iSimangaliso Wetland Park, looking for nesting female Leatherbacks. The nesting season is crucial for turtle researchers as it provides the only opportunity to physically handle the animals, as Gaisford explains: “The Leatherbacks are huge animals and they’re incredibly fast in the water. Other than netting them, you have actually no chance of catching them, and drugging is not an option because you run the risk of drowning them. This is why these nesting beaches are so valuable, because we have the opportunity of measuring the animal and putting a transmitter on it.”
The ideal when attaching transmitters is to find a female laying her eggs. During this time, the animal goes into a trance-like state and it’s possible to approach her without resistance. But finding the animal at exactly the ideal time is harder than it sounds, says Gaisford, who drove the project team during their turtle hunts.
“We would sometimes drive from Sodwana right to Kosi Bay and back. It’s a lottery. You have to be travelling up at the same time that it is coming ashore and your paths have got to cross. Sometimes they come ashore just behind you or they come ashore ahead of you and they’re on their way back. Timing is critical.”
Unfortunately for the team, conditions weren’t ideal for any of the three catches: one turtle was right up against a steep sand bank making it difficult for the team to attach the transmitter harness, and the other two were moving, one heading back to the sea and the other covering up her nesting hole. Gaisford still bears the scars of being knocked flying by a well-placed flipper, and in the end, it took the exhausting efforts of six people to eventually attach the harnesses.
While the conditions were not ideal, the team are hoping that their decision to harness the animals at the end of the nesting season will pay dividends. “The last couple of seasons we put transmitters on at the start of the season, which gave us some interesting movement data while they were offshore and nesting. But the problem with that is that every time an animal comes ashore, it’s a huge strain on the harness and we think that that may have weakened it and led to the premature loss of the rigs (three to four months after the initial harnessing). This year it is hoped that the harnesses will survive a little longer and the team will be able to add another piece to the puzzle of where these far travelling animals go. “Each of the countries where Leatherbacks occur is doing their own research on what their populations are doing and we’re helping to add to the global knowledge about how these animals move. We are honouring our side of the agreement we have with the international community to research and protect this animal, and as the longest running Leatherback conservation project in the world, we’ve got a commitment to continue this.”
Nets and fishing methods that pose a threat sea turtles
Drift Nets or Gillnets
So called because fishing boats leave them to float in the ocean to catch more fish, which are then trapped by their gills. These nets are popular with fishing fleets in Japan, Korea and Taiwan and during the fishing season, Asian fleets set more than 32 000 km of nets each night. Each net is between eight and 20 metres deep and ranges in length from 32 to 120 km. The mesh size of the net is determined by their target catch (allowing smaller fish to pass through) but anything larger (including sea turtles and other marine animals) can easily become snared. They are virtually invisible underwater (especially at night when they are usually used) and kill anything in their path as they drift with the current. Because of this they have been nicknamed “The Wall of Death”. Large pieces of net often break off during fishing operations and continue killing until it is believed that they eventually sink from the weight of the dead fish and marine animals caught in them. These are referred to as “ghost nets”.
According to Greenpeace, one dolphin will be drowned for everynine tuna caught by gill nets in the South Pacific, and it is estimated that more than 85 000 marine mammals (including 70 000 dolphins and porpoises and 14 000 seals) are drowned annually in the nets of the North Pacific drift net fishing vessels.
In July 1989, South Africa banned all drift net fishing in their oceans (along with countries like New Zealand and Australia), and at the end of 1992 the United Nations moratorium on the use of high seas drift netting became internationally operative.
EKZNW officers in KwaZulu-Natal and Marine and Coastal Management officers in the Cape do regular inspections on South African fishing boats and arrest any who have gill netting on board.
Long-Line Fishing
Kilometres of single lines are placed out in the ocean, with buoys marking their position. Suspended from the lines are hundreds or even thousands of baited hooks, primarily aimed at catching high value fish such as blue fin and yellow fin tunas and swordfish. In some areas it is not unheard of to have as many as 2 500 hand-baited hooks on a single series of connected lines. It is estimated that the world’s long-line fleets use over a billion hooks annually. Long lining is controversial, however, because of its large by-catch (species that are caught by the lines, but that not targeted by the long-liners, and will most likely be discarded). These include different species of fish, seabirds and sea turtles that get snagged in the hooks and then drown. To combat this in South Africa, EKZNW and conservation groups are trying to encourage long liners to change from their tradition J-shaped hooks to new hooks with a more curved design, which will allow sea turtles to escape or detach themselves if accidentally snagged.
According to Jeff Gaisford: “These new hooks aren’t any more expensive than the traditional ones. It’s just hard to break the traditional mindset, although there is quite a lot of work going on in the background on the fisheries side to reduce the by-catch.”
Trawl-nets
Trawl netting is a specific type of fishing that drags a fishing net along the sea bed (or sometimes just above it), aimed mainly at catching small fish and prawns. According to Gaisford: “A huge percentage of what trawlers catch is not what they’re looking for and it gets chucked over the side, dead. Trawl nets are very non-specific.” And this effects sea turtles too.
Purse Seine Nets
Seine nets are vertical nets that are placed in a circular pattern to enclose big schools of fish (usually tuna). The ends are then drawn together to trap whatever is within the circle. Once again the issue is of non-selectivity and often sea turtles, as well as bigger animals like dolphins and seals become part of the by-catch.
Sources: www.wikipedia.com, www.botany.uwc.ac.za
How the Turtle Transmitters Work
The transmitters used for this project are cube-shaped and attached to a base plate that sits on the hump of the animal.
The base plate is attached to the animal using nylon strapping, encased in soft plastic tubing to prevent chafing. The tubes sit across the muscles of the animal’s shoulders much in the same way as a backpack and then the straps are pulled tight under the animal and secured with rings.
The rings are made of ordinary steel (as opposed to stainless steel) so they will rust and ultimately fall off. The harness is designed so that if any of the rings fail the animal will be able to easily slip out of it, and is expected to last for about a year. The batteries are also designed to last for a year, and while bigger units are able to record depth of dives, these give only coordinates thereby conserving the battery life of the pack.
Whenever the animal comes to the surface to breathe, the transmitter sends the animal’s co-ordinates via a signal to a French Satellite, known as the Argos. This information is then e-mailed back to Marine and Coastal Management in Cape Town, who forward it to the relevant research parties who analyse the data. Marine and Coastal Management are funding the cost of the transmitters at R18 000 each and the satellite fee of R5 000 a month.
* Witness the Wild is a Weekend Witness-sponsored page that aims to raise awareness of the importance of conservation in our province and covers the news and work of non-profit organisation the Wildlands Conservation Trust and KwaZulu-Natal's formal conservation body Ezemvelo KZN Wildlife. Please visit www.wildlands.co.za and www.kznwildlife.com for more information.
