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Originally published May 9, 2009

Although Batman and Robin’s shark repellent was effective (see below), it had disastrous repercussions for the shark:

Shark explosions are clearly undesirable for those of us shark-lovers out there, so we’ve been looking for new methods. Researchers Eric Stroud and Michael Herrmann from the organization SharkDefense have discovered that sharks have a strong aversion to magnets made from neodymium, iron and boron.  The researchers on the project believe that the metal combination disrupts the shark’s ampullae of Lorenzini, electroreceptors that the shark uses to detect electric fields.  Sharks may use electric fields to detect prey and have been shown to home by the use of geomagnetic fields.

In the video below, the black line contains the repellent magnets and you can see that the lemon sharks don’t cross the line:

The magnet is so powerful that it’s able to jar sharks out of the tonic immobility that they exhibit when turned on their backs:

This discovery can have lots of useful applications.  First of all, there are lots of nets around the world meant to keep sharks out of specific areas (areas where people swim often, for example) and these nets end up capturing and suffocating lots of sharks each year.  If these nets were outfitted with this new magnetic shark repellent, then the same end could be achieved without unnecessary shark deaths.

Also, fishermen can use these repellents to keep sharks off their fishing line.  Not only is this great for the sharks, but it’s great for the fishermen too, who would rather have fish that will fetch a good price at the market on their line than of a shark.

Unfortunately, the metals are too heavy to be integrated into diver’s suits, so you won’t see divers benefitting from this shark repellent anytime soon.

My only concern with this finding is that, by disrupting the activity of the shark’s ampullae of Lorenzini, widespread use of the magnet may interfere with the shark’s ability to navigate and home by the earth’s geomagnetic field.  Since we don’t know much about where sharks go and when, it may be hard for us to determine if we are or aren’t effecting their movement behaviors.  The researchers report that the magnets don’t have strong repellent effects on the sharks until they are within 10 inches of the magnet, but it’s possible that it could be having more subtle effects at a distance.

It’s possible that the magnets won’t be a problem because their use won’t be widespread enough or their density won’t be great enough to detected by the sharks, but I think it’s an important point to keep in mind.

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