The physics of shark repellent

duh, duh….duh, duh….duh, duh… OH NO!!!!!!!

After a recent trip to the Air and Space Museum had me laughing hysterically at the shark repellent displayed in a U2 pilot survival kit, I did the natural thing and googled it. I was seriously surprised by what I found. So, in honor of Shark Week – the annual holiday as declared by Discovery Communications – I wanted to harp on some seriously suspect physics I noticed while looking up shark repellent bat sprays.

Two separate devices I found are being sold to this effect and from the looks of it, people are really buying. The first, called Aquashield, is using physics that seems about as likely to save you from a great white as a magnetic bracelet is to save you from Magnetic Field Deficiency Syndrome. And as near as I can tell from their Wikipedia regurgitation of irrelevant facts and the following email correspondence, it is a magnet.

Inquiring email to Aquashield:

Our Question:

“So, it’s a magnet?”

Aquashield Answer:

“Thank you for your interest in the Aquashield unit.

Yes you are correct, the unit utilizes integrated magnetic technology as part of the process to achieve this excited state of electrons. The flow through ports allow for the ionization process to take place. The field arrangement is such that the exothermic polymer allows for a stabilized field state so this field structure is never compromised. There are 24 sequential magnetic points that deliver this field state.

Hope this helps”

The magnet belt-buckle does have a pretty sweet logo on it, and if I were a hipster I might procure one just to put all other hipster belt-buckles to shame. It’s funny at first and then you realize people are actually thinking this makes them safe. Snake oil is one thing, but if you sell someone snake oil the risk of it not working doesn’t involve being eaten by a snake.

The other similarly named device, called Shark Shield, is at least more active, though $500 more expensive. This one supposedly works by sending out an electromagnetic wave that causes uncontrollable muscle spasms in any shark in your area.

According to Shark Shield’s website:

Shark Shield is a three-dimensional electrical wave form which creates an unpleasant sensation impacting the shark’s ‘Ampullae of Lorenzini’. When the shark comes into proximity of the electrical wave form (around 8 meters in diameter) it experiences non-damaging but uncontrollable muscular spasms causing it to flee the area.

The field is projected from the unit by two electrodes, which create an elliptical field that surrounds the user. Both electrodes must be immersed in the water for the field to be created. The electrode configuration depends on the model of the Shark Shield unit.

From testing, the closer the shark is to the Shark Shield field, the more spasms occur in the sharks’ snouts. This becomes intolerable and the shark then veers away, and usually doesn’t return.

Sadly, a person was actually killed while wearing the device several years ago according to this article. Also, according to the same article a raft in South Africa was moving along with the Shark Shield attached to it when a 12 foot shark came up and ate the device.

One interesting thing about this though, is that sharks really do have the ability to detect electrical impulses. Sharks – as well as stingrays and some other aquatic creatures – have a number of electroreceptors in pores on their heads called ampullae of Lorenzini. This is how they hunt and possibly how they can navigate such large distances.

Does this translate to a shark being repelled by a magnet or an EM field? Neither company presents very compelling evidence. Shark Shield is supposed to cause uncontrollable muscle spasms in sharks, but in none of the videos posted on their website did I see that happen. Just because you survived a shark swimming near you doesn’t mean the device worked. People swim by sharks all the time. They rarely attack.

However, one good thing about working in a building full of physicists is that you always have materials on hand for experiments, yes even bountiful strong magnets and sharks. I think our experiment is about at the level of their science, but I’ll let you be the judge. Clearly the results of this experiment show that a Bala shark would be no less likely to eat you if you were wearing magnets. If the maker of either of these products cares to post any sort of evidence for the validity of their products, I more than welcome it.

Physics Buzz: We put magnets in a fish tank with our boss’ Bala Sharks, you decide.

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