South Africa Rethinks Use of Shark Nets
for National Geographic News
|June 4, 2002|
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For close to 40 years, South Africa's Natal Sharks Board (NSB) has been protecting swimmers against shark attacks. In the last several years, the agency has added protecting marine life, including sharks, to its mandate.
Miles of protective netting were installed at resorts along a 200-mile (320-kilometer) stretch of the KwaZulu Natal province's coastline after a series of shark attacks in the 1950s and 1960s. The netting protected tourists at the popular coastal resorts, but scientists discovered that a disturbing number of sharksmany of them harmlessstingrays, turtles, and dolphins were also being caught.
"There needs to be a balance between safeguarding tourists and limiting harm especially to non-targeted marine life," said Jeff Gaisford, spokesman for KZN Wildlife, the province's nature conservation and ecotourism authority.
To fulfill this dual mandate, the NSB has been exploring alternative protection measures, while slowly and selectively removing some of the netting. Three years into the program, NSB scientists are satisfied that this can be done without undue risk to bathers.
Durban, South Africa's most popular holiday city, installed nets in 1952 following a series of shark attacks, several of which were fatal. The city suffered no more serious attacks, but several netless resorts a short way off did. During one horrific period known as "Black December," five people died in shark attacks over a 107-day stretch, from Christmas 1957 to Easter 1958.
Several solutions were attempted by local authorities desperate to lure back panic-stricken holidaymakers. Unsightly enclosures built of wooden poles, wire, and netting were erected, only to be smashed by the rough surf. A South African Navy frigate dropped depth-charges in shark-infested waters. Only a few sharks were killed, and many more were attracted by the dead fish.
Finally, in 1964 the then-Natal (now KwaZulu Natal) provincial authority established the NSB to take charge of bather safety along its coastline. The NSB responded by installing nets at most major resorts.
The nets do not provide a physical barrier between sharks and bathers, said Sheldon Dudley, senior researcher at the Natal Sharks Board. Their function is to catch sharks, thereby keeping their numbers down in areas used by bathers.
The nets are about 656 feet (200 meters) long and about 19 feet (6 meters) wide. They are fixed to buoys anchored to the seabed in water about 40 feet (12 meters) deep. Sharks can swim over, under, and between them.
The nets reduced shark attacks by 90 percent, catching an average of 1,245 sharks per year. But the nets are indiscriminate, catching not only the shark species primarily responsible for attacksZambezi or Bull sharks, Great Whites, and Tiger sharksbut also a large number of harmless shark species, as well as dolphins, stingrays, and turtles.
NSB staff tend the nets 20 days each month, and all live animals, including dangerous sharks, are released. The sharks and some rays are tagged. Most of the dead sharks are taken to the NSB laboratory for research. Still, marine biologists considered the level of by-catch unacceptably high.
Investigations showed that there were simply more nets than necessary. By reducing the number, and by cutting out their overlap, researchers determined it was possible to reduce the by-catch without increasing the risk to bathers. The research was backed by practical findings from Queensland and New South Wales, Australia.
"Nets have been reduced by 25 percent since 1999, to about 18 miles (29 kilometers). This has resulted in fewer animals getting caught, but it is too early to put a figure to it. We have to wait to see if it is consistent," said Dudley.
Shark Net Alternatives
The NSB is also looking at other ways to limit ecological damage without endangering bathers.
One is the use of "drumlines"floats (recycled oil drums) that are anchored to the seabed, with baited hooks attached. The baited hooks are particularly alluring to sharks, and mostly only to the species targeted. Experience in Queensland has shown that some turtles unfortunately also tend to take the bait, but dolphins and stingrays do not.
The NSB is looking at how many drumlines it would take to replace a net, and whether a combination of drumlines and nets would be effective.
An electric device called a Protective Oceanic DevicePOD or "SharkPOD" for shortis useful to individual divers. Since sharks are known to be sensitive to electricity, the SharkPOD creates an electric field around the user. It is expensive, however, and used mainly by commercial divers. The NSB has entered into an agreement with an electronics company to create a smaller device for divers and additional configurations for other user groups.
Another idea under consideration is the possibility of surrounding an entire bathing area with an electrical barrier.
Attaching pingers to the shark nets may help reduce dolphin catches. The battery-operated device sends out a pinging noise that scares the dolphins off. It is already in use in one area frequented by dolphins.
The NSB continues to work closely with local authorities as nets are removed.
"Whatever move we make, we need first of all to ensure it will not endanger the lives of bathers," agreed Graeme Charter, director of the NSB. "Safeguarding bathers is the reason the NSB came into existence."
It's shark week at National Geographic News. Tomorrow we will feature a story on lemon sharks.
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