麻豆传媒

THE water is murky but every now and then the dark shapes circling me come close enough to make out. They鈥檙e sharks. I鈥檓 in a pen with six of them.

OK, so the water is only waist deep and the sharks are barely a metre long. But when you鈥檙e testing a shark repellent, it is wise to start with the small ones.

A few weeks earlier I had heard about a company called Shark Defense of Oak Ridge, New Jersey, which claims to have invented a chemical repellent that actually works. There have been plenty of similar claims over the decades, yet few products have ever reached the market and none has proved truly effective. Could Shark Defense have succeeded where so many others have failed?

It turned out that although the company鈥檚 claims have been widely reported, no journalist had been to see the repellent in action. So when I found out the next tests were being held in Bimini in the Bahamas, I got in touch and begged for an invitation.

Bimini is a tiny cluster of islands about 100 kilometres east of Miami, inhabited mostly by vicious mosquitoes and, of course, surrounded by shark-infested waters. It is also home to the Bimini Biological Field Station, the Shark Lab to locals, an independent research centre crammed full of tanned volunteers who spend their days studying the young lemon sharks for which Bimini鈥檚 lagoons and mangrove swamps serve as a nursery.

The Shark Lab was set up in 1990 by renowned shark researcher Samuel Gruber of the University of Florida. Gruber, who still owns and runs the lab, worked on a repellent for the US navy in the 1970s. So when the founders of Shark Defense, Eric Stroud and Mike Hermann, wanted to test their repellent, Gruber was the natural person to turn to.

For the latest tests, Stroud, Hermann and Doc, as everyone on Bimini calls Gruber, fly in with a huge pile of equipment. Stroud and Hermann are not quite the tough diving or surfing types I expected. Stroud works as a consultant in the chemical industry, while Hermann is an electrical engineer.

As they unpack their gear at the Shark Lab, I get my first whiff of the repellent, a clear yellowish fluid. It has a sickly sweet, almondy smell 鈥� not particularly unpleasant at first, but it soon gets to you.

That afternoon we set off in a small speedboat in search of bull sharks, one of the most dangerous species. It is the only shark that can move freely between salt and fresh water: bull sharks have even been found 4000 kilometres up the Amazon. The place to find bull sharks here, though, turns out to be the docks along the front of Bimini鈥檚 main town, Alice Town. This is where sports fishermen gut their fish, and the bull sharks have learned to visit the docks in the late afternoon when the scraps are being tossed into the water.

鈥淭here were a lot of stinky nights. The raw extracts of rotten shark were pretty brutal鈥�

We moor up and Grant Johnson, the lab manager, starts throwing chum and fish heads into the water while Hermann sets up a video camera to record the test. Then we wait. And wait and wait, while the sun goes down and the mosquitoes swarm around us. A couple of huge stingrays come to feed but no bull sharks.

The trouble is that it is September, and Hurricane Frances swept by a few days earlier. It did little damage to Bimini but Alice Town is still a ghost town with many houses and hotels boarded up. A local tells us that the bull sharks haven鈥檛 been seen since the hurricane.

Eventually we give up and head back to the lab. Hermann goes to bed early having accidentally sprayed himself with repellent and developed a nasty headache. Stroud and I head to a bar for a beer and a chat. 鈥淭he media coverage of shark attacks during 2001 was very intense, lots of people were bitten,鈥� he tells me. 鈥淚 got interested in the idea of repellents and started reading about the historical efforts.鈥�

The first serious attempts came during the second world war when US servicemen were issued with cakes containing a mixture of copper acetate and a black dye. These boosted morale 鈥� the prospect of surviving a torpedo attack only to be eaten by sharks is hardly an enticing one 鈥� but the consensus now is that if the cakes worked at all, it was only because the clouds of dye may have scared off the sharks.

In the 1970s, the US navy enlisted a team of researchers, including Gruber, to try again. Sharks were occasionally attacking and disabling sensors trailed by submarines, and the navy wanted to find a way to keep them off. So the team went to the Red Sea to study the Moses sole, which produces a toxin called pardaxin that repels sharks. The secret, the team found, is that its surfactant-like properties damage sharks鈥� gills. Other surfactants, such as sodium dodecyl sulphate, turned out to be even more effective, but they are not very practical as repellents: they work only if squirted directly into a shark鈥檚 mouth.

In the 1980s, South Africa鈥檚 Natal Sharks Board began experimenting with electric fields. In 1996 it marketed the SharkPOD, a bulky device for divers that it claimed repelled the big three 鈥� bulls, tigers and great whites. The technology is now licensed to SeaChange Technologies of Adelaide, South Australia, which is developing smaller versions.

It seems clear that certain kinds of electric fields do repel sharks, but there are still question marks over the commercial device鈥檚 effectiveness. In 1997 a film crew attached an active SharkPOD to a tuna. The fish was promptly eaten by a great white. Divers testing the device have reported attacks, and in 2002 a great white killed an Australian scallop diver wearing a SharkPOD.

As a chemist, Stroud was struck by the old fishermen鈥檚 tale that rotting shark carcasses repel other sharks. So he set about trying to extract the essence of rotting sharks to see if it was true. 鈥淭here were a lot of stinky nights,鈥� he admits. 鈥淭he raw extracts were pretty brutal.鈥� Soon he enlisted the help of Hermann and hired a lab, much to the relief of his wife. Then, in 2003, they went to the Shark Lab to test the extracts.

Jaw-dropper

The staff were sceptical. Others had come out to Bimini to test repellents and none had worked. 鈥淲e thought, who are these two goofy guys from New Jersey,鈥� says Johnson. 鈥淲hat do they know about sharks?鈥� Yet to their astonishment, one of the extracts appeared to work. 鈥淒oc鈥檚 jaw just dropped,鈥� Johnson says.

On the second day we set out for another test. This time we鈥檙e going after Caribbean reef sharks, which rarely attack humans unless provoked. For nearly a decade, the lab staff have been going out to feed reef sharks at a site called Turtle Rocks. This makes it a great location for testing repellents as the sharks have grown accustomed to boats and people.

The turquoise water off Turtle Rocks is beautifully clear. Dozens of triggerfish come to the surface to feed on the chunks of fish being tossed in but there is no sign of sharks. Half an hour goes by. Finally a single shark appears out of the blue 鈥� and is gone as suddenly as it appeared. It鈥檚 clear that today鈥檚 test isn鈥檛 going to happen either, so we head back to the lab to try another method.

Hold a shark upside down and after a while it goes limp 鈥� a state called tonic immobility. In theory, an effective repellent should rouse a shark from this state. And that鈥檚 where the shark pen comes in.

We wade out to the pen armed with about 20 different formulations of the repellent. The latest version is a mixture of chemicals, and Stroud still isn鈥檛 sure exactly which one, or more likely which combination, does the trick. One by one the young lemon sharks are caught and put into tonic immobility by the handler. Stroud squirts the test chemical at their snout, and Hermann records the time it takes them to respond and how much repellent was required. Water has no effect, nor does a dye. Nor, indeed, do some of the chemicals. But some clearly do have an effect. One makes a shark thrash about so violently that it escapes the handler鈥檚 grip and shoots off into the lagoon.

鈥淎fter 45 minutes he was screaming in pain. At that point, they stabbed the shark in the head鈥�

So far so good. But will the repellent work on big sharks in feeding mode? We head back to Alice Town to try to lure in bulls. Stroud and Hermann, who have ended up spending a lot of time trying to attract sharks rather than repel them, deploy their latest gadget: an underwater loudspeaker designed to mimic the sound of a dying fish. We do get plenty of bites 鈥� but only from mosquitoes. As evening falls we flee far out to sea and spend the night in search of tiger sharks, but there is not so much as a nibble.

The next day it is back out to the pen to try the repellent on two young nurse sharks. These are a common sight in tropical waters and are harmless, unless you are foolish enough to prod one. Then there鈥檚 a risk of learning the hard way that when nurse sharks bite, they don鈥檛 let go.

鈥淭here are stories of people being taken to hospital with the shark still attached,鈥� Johnson tells me. He once had two fingers bitten while trying to release a nurse shark caught on a fishing line. The team tried everything they could to make it let go: prying open its jaws, hammering at its mouth, suffocating it by shutting off its gills. 鈥淎fter 45 minutes I was screaming in pain,鈥� he says. At that point, they stabbed the shark in the head.

We recreate the incident, this time with fish instead of fingers. Sure enough the sharks latch on and don鈥檛 let go. Then Stroud tries a squirt of the repellent and the sharks let go within seconds. So it鈥檚 full marks on this test: if you get bitten by a nurse shark, a bottle of this stuff will definitely come in handy.

But what about keeping sharks away in the first place? Our attempts to test the repellent on larger sharks are not going well. Two more trips to Turtle Rocks end in failure. 鈥淭his has never, ever happened before,鈥� Gruber tells me.

It seems that the hurricane has driven all the bigger sharks to deeper water. But we know the lemon sharks have returned because many of them are carrying Shark Lab tracking devices. So on the last day we set off to the north lagoon, nestled within the v-shape of the main island. Out goes the chum, and we watch eagle rays scooting up and down by the mangrove trees. It鈥檚 a wild, beautiful place, but it鈥檚 not going to stay this way for long: the Bahamian government has approved plans to fill in the lagoon to create a golf course.

After about half an hour dark shadows start to appear. They鈥檙e lemon sharks, but they are wary. They circle far from the boat, making occasional forays towards us. After another half an hour, none has come closer than 15 metres. And we鈥檝e run out of time.

So I never did get to see the tests on big, wild sharks. Instead, they showed me video footage from a previous test at Turtle Rocks. And it is impressive. As soon as the repellent is released into the middle of the feeding reef sharks, they scatter. A shark that has been lurking off to the side then comes in to grab a bit of fish. The instant it hits the cloud of repellent it jerks its head away violently and shoots off. Other fish seem oblivious to the repellent.

Shark Defense has also found it works on blacknose, lemon, nurse, blue and bull sharks, though they have yet to test it on great whites. But how and why the repellent works is still a mystery. The suspicion is that it acts like a pheromone or signalling chemical triggering some ancient response mechanism shared by many shark species. Yet why would such a substance be found only in rotting shark flesh?

Whatever the explanation, it does seem to work. So is this the answer to our fear of sharks? Everyone envisages swimmers and surfers smearing on a sunscreen-type repellent. But Stroud is dismissive. 鈥淚 worked on sunscreens for seven years. It鈥檚 not going to happen.鈥� Creating a repellent that won鈥檛 wash off is very difficult, he says. Even if it could be done, it would probably provide half-an-hour鈥檚 protection at best. A more practical option would be a repellent gun that divers could carry with them in case sharks become aggressive. I would certainly feel safer carrying a gun on dives where I might encounter dangerous sharks.

But surfers and swimmers are unlikely to want to carry a gun. And if they don鈥檛 see the shark coming, it might of limited use anyway. So perhaps it鈥檚 just as well there appears to be little need for a repellent. The International Shark Attack File lists just 55 unprovoked attacks worldwide in 2003 (see Table), and even the so-called 鈥渟ummer of sharks鈥� in 2001 was nothing out of the ordinary. In the US sharks have killed only 22 people since 1959, while lightning has killed nearly 2000.

But Stroud and Hermann have a different application in mind. Each year long-line boats fishing for swordfish or tuna inadvertently catch and kill millions of sharks, one of the reasons for the serious decline in shark numbers (see Chart). So the idea is to add repellent to long-line baits, which should repel sharks but not the swordfish or tuna. And it doesn鈥檛 have to be totally effective to be useful. 鈥淎 50 per cent reduction in the by-catch would be great,鈥� Stroud says.

The idea has yet to be tested, as Stroud is still working on a slow-release formula. But the US National Oceanic and Atmospheric Administration fisheries service has shown some interest, and the pair are negotiating with potential investors. Let鈥檚 hope it works. I really like the idea that the main use of shark repellent will not be to save people from sharks, but to save sharks from people.