Could dead sharks deter live ones?
WHILE the great shark net controversy rages, scientists keep searching for alternative, more environment-friendly means of personal protection against shark attacks.
Nets, shields and other physical barriers are most commonly used, the problem being they are expensive to maintain, at the mercy of rough seas, and indiscriminate in terms of the other large species they kill.
At present, conventional meshed shark nets and drumlines (large baited hooks) are deployed at beaches in KZN (the only province that uses shark nets).
In fact, nets are not designed to prevent sharks from entering a bathing area; they are designed to kill sharks, on the premise that ‘fewer sharks means fewer attacks’.
It needs bearing in mind that surfers and spear fishermen – who rarely are found inside netted areas - account for the majority of shark attacks.
Besides methods that try to render a potential victim less visible to sharks, or to detect their presence via satellite tracking, modern research is homing in on the shark’s physiological responses to light, sound and – especially - electrical or magnetic fields linked to the creature’s electro-receptive system.
But there is also another area of research gaining increasing attention in the form of chemical repellents.
Responding to a recent Zululand Observer editorial comment, Mtunzini resident Burgert Roberts referred readers to experiments taking place in the Cape where dead sharks are being used to scare off live ones.
‘Essence of dead shark’
The experimentation is being led by Kokstadborn Collin Brooker and his son Simon, now based at Fishhoek in the Cape.
After living in the UK they moved to Australia where they witnessed and were appalled by mass shark culling in the early 2000s.
Having seen a BBC documentary on an American scientist who had discovered that artificial scent replicating the smell of dead sharks was able to repel live sharks, Collin developed the Podi – a small personal protection device that slowly releases the chemical into the water.
The device, which can be attached to a surfboard or worn on the person, slowly releases a chemical formulated on the scent of dead shark.
This chemical continuously dissolves in water and appears to be giving positive results.
We put this theory to Geremy Cliff, head of research at the KZN Sharks Board, who sent the following response:
‘The use of chemicals found in rotting shark meat as a shark repellent/deterrent has been around for decades.
‘I have never used it nor seen it in action, but I would willingly use it in a dangerous situation, for example when diving around a seal colony where there is a good chance of bumping into a Great White shark, or when surfing on the Wild Coast, especially in summer when the water may be murky after heavy rains.
‘The US Navy developed a product called a Shark Chaser towards the end of WWII and issued it for several decades.
‘It resembled a cake of soap and gave out a rotting shark smell in the form of copper acetate together with a nigrosine dye which discoloured the water and ‘hid’ the user from sharks.
‘It provided a very short period of protection, but hopefully long enough to enable the user to be rescued if his vessel was sunk at sea,’ said Cliff.
‘I don’t think its use is practical as a form of mass protection in the case of large numbers of bathers swimming at a surf beach such as Alkantstrand, where the chemical would be rapidly dispersed by waves and currents.
‘Given the unpleasant odour of a rotting shark, I am sure that Podi or any other product would be not be popular with the average beach tourist.’