In our current Planet Shark exhibition there is an entire section on how not to get attacked by a shark. Apart from physical protection such as steel cages and chainmail suits it features a number of chemical repellants, none of which are very effective, apparently. (In one case that’s primarily because the repellant is enclosed in the skin of a diving suit and only released when the shark bites trough it, which is of course a bit late…)
There is one technology, though, that can be effective in turning away an approaching shark, we are told. In the exhibition, it is represented by three different models of the Shark Shield equipment. However, the exhibit offers no explanation as to how this shield is supposed to work, so here’s an attempt to fill that gap:
Animals produce very weak electric fields whenever they move a muscle, and sharks are able to sense these electric fields with an array of electroreceptors called ‘ampullae of Lorenzini‘. To be of any use in prey detection, these receptors have to be extremely sensitive. But when the shark unexpectedly meets a very strong electric field, the resulting overstimulation causes the shark to turn away and avoid the waters around that field.
Using two electrodes separated by a certain distance and powered by a battery, the Shark Shield equipment creates such an electric field around a person in the water. This creates an ‘exclusion zone’ extending 3-5m away from the person, which is still pretty close to get to a hungry shark, if you ask me. But even a short distance may make the difference between being bitten and just being scared to death.
However, how well this shark repellant really works probably depends on exactly how hungry the shark is…