29 November 2004

Raggy (Ragged toothed shark) project

Conservation today is about bridging the divide between human beings and the environment, to ensure long-term, sustainable solutions. The Green Trust has been a pioneer of this approach, and supports projects that encapsulate it. Diving with ragged tooth sharks is such a project.

Most people fear and hate sharks. But the reality is that sharks have far more reason to fear humans. Over 71-million sharks and their relatives, rays, are killed in commercial fishing activities each year. This does not include those taken accidentally as by-catch and those thrown overboard.

The risk of extinction is high for many species of sharks and rays. They are used for their meat, fins, cartilage, leather, oil, gills, jaws and teeth. Sharks are slow growing, produce few young, and can take many years to reach sexual maturity. They are extremely vulnerable to over-fishing and once a population has been severely exploited, it could take decades for it to recover, assuming it recovers at all.

Fortunately there are growing numbers of tourists wanting to see sharks in their natural environment. Scuba-divers in particular seek out opportunities to dive with sharks of various kinds. But diving with sharks is risky ? for both the divers and, to the surprise of many, the sharks themselves.

Divers come from around the world to South Africa to dive with sharks, such as the ragged tooth shark, CarchariasTtaurus (or ?raggies? as they are locally known). Despite their large size and fearsome rows of sharp teeth, raggies are docile and allow divers to approach within a few metres. In winter and spring, ragged tooth sharks can be readily seen on the Aliwal Shoal ? a submerged reef on the east coast of South Africa, 50 kilometres south of Durban.

Raggies are fascinating creatures. Mothers give birth to two live young which spend their first few years in the waters of the Eastern Cape. When they?re old enough, the youngsters join the adults on the annual migration up the east coast to northern KwaZulu-Natal and southern Mozambique. On the way, they spend some time at offshore reefs such as the Aliwal Shoal, where they may engage in courtship and mating.

In recent years, concerns have been raised that the raggies are being disturbed by diving activities at the Aliwal Shoal. Local operators and researchers have realised there is a need for more information about the raggies and their habits. A project currently being undertaken is looking into the impacts of scuba diving in this area.

The raggies can be individually identified by the cuts and notches in their fins, in addition to the spot patterns on their flanks. Photographs of these sharks taken over the past few years show that many of them repeatedly return to the Aliwal Shoal, but there appear to be fewer every year, although there is no known reason for this.

Some raggies have also been tagged with radio tags (pingers), which give off a high-frequency signal the sharks can?t hear, but which is detected and logged by underwater receiving stations. This helps us track the 24-hour movements of individual shark, in order to determine whether they are being disturbed, and move away when divers approach the caves and overhangs where the raggies rest during the day.

Globally the ragged tooth shark is currently listed as ?vulnerable?, although our raggie population in South Africa appears to be stable. Provided fishing restrictions remain, and scuba divers follow responsible diving guidelines when diving with raggies, our ragged tooth sharks should be safe for future generations of divers to enjoy.

For more information contact:
Mieke van Tienhoven
E-mail: raggie@posix.co.za

Prof. Vic Peddemors
E-mail: vmp@pixie.udw.ac.za

Website: http://sharks.csir.co.za


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