About 100-million sharks, rays and skates are being killed every year, and experts predict that if this current rate continues, in 20 years many species will become extinct.
Already it has been established that some species of shark face the risk of extinction having dropped in population numbers by 89% between 1986 and 2000.
Sharks are considered reliable bio-indicators of the ocean’s health and considerable research needs to be conducted if conservation projects are to be successful in saving these ocean predators from extinction.
Senior specialist scientist Malcom Smale at Bayworld in Port Elizabeth is currently involved in shark research using tagging and tracking devices to learn more about the movements and behaviour of sharks.
‘Locally we are studying ragged-tooth sharks and we have discovered that they tend to return to reefs that they have been located at before,” said Smale.
One ragged-tooth shark that has become a local celebrity is Maxine, who was released back into the ocean in March last year by the Two Oceans Aquarium after 10 years in captivity.
Smale and his colleagues are using an ultrasonic tag and two pop-off archival transponding (PAT) tags to track the movements of Maxine after her release. It was expected that she would join the eastward migration of the ragged-tooth sharks.
‘They [the Two Oceans Aquarium] want to know whether she will integrate with other sharks in the wild population,” said Smale.
An ultrasonic tag broadcasts a signal at a high frequency, outside of the sharks hearing range, which is picked up when the shark is within 300m to 500m of a listening station, positioned along the coast.
‘If you imagine these listening posts as bus-stops on a route, by identifying the stops they have been at, we can track their path,” said Smale.
‘These tagging systems have provided us with all kinds of new information about the movements of sharks,” said Smale.
Maxine’s first PAT tag set to be released on June 15 last year failed to transmit, while her second tag released on September 11 surfaced off Plettenberg Bay, 298km east of her release point.
Maxine is set to be joined by another of her Two Oceans compatriots, when a further ragged-tooth is released this year. Smale said that a shark from captivity and one wild-caught animal would be tagged together so that they could compare the behaviour of the sharks.
Smale says they plan to expand their ragged-tooth shark research this year through the increase of sharks tagged with ultrasonic tags.