Does Shark Repellent Actually Work? Here's What Science Says

The fear of sharks appears to have been ingrained in children of every generation since "Jaws" first hit theaters in 1975. While shark attacks on humans are incredibly rare, a deeply-embedded sense of fear can prevent many from venturing into the ocean. Additionally, these fears can lead to unnecessary provocation and violence towards sharks. Thus, many have searched for solutions and profited from claims to reduce the chance of such encounters. Among these solutions are shark deterrents. These typically aim to disrupt sensory systems within sharks, including olfaction (the sense of smell), electrosensory perception, and vision. But, the efficacy of these devices have been shown to vary, and nothing so far has been determined to fully prevent shark bites.

Among all the types of shark deterrents that exist, there does seem to be a winner. Devices that disrupt electroreception have a bit more science to back them up than others. Sharks have receptors that gather electrical information from their environment, known as the ampullae of Lorenzini. While this might not sound very useful at first, it helps to understand that living things are emitting weak electric signals all the time.

We emit electric impulses from our nervous system and contractions of muscles, such as a heartbeat. Additionally, the matter that comprises our physical makeup contains ions, which are atoms with an electric charge. The salt of the ocean is composed of sodium chloride, which is simply the elements sodium and chlorine. Each of these elements has a charge, with sodium having a positive charge and chlorine having a negative charge. The ionic composition of our cells is different from that of the saltwater, so as they interact, a small voltage is generated.

A fish traveling through the ocean and a human swimming both generate a weak electric current that can be interpreted by the sensitive receptors on the shark's head. Such information is useful in detecting both predators and prey, making the shark a strong hunter. The theory of these shark deterrents is that by creating an electromagnetic field through such devices, sharks become confused and disoriented, encouraging them to swim away.

While this might appear like a very sound method of aversion, the odds are likely not as great as you would hope. For instance, a 2024 publication revealed that two different commercially available shark deterrents reduced the probability of shark bites by 54%. While that is certainly an effect, it is important to acknowledge that it does not fully remove the chance of a shark bite. Still, how these odds could vary in a real-world scenario is unknown.

To perform these experiments, the researchers often set up a sort of shark cornucopia. Usually, these repellent devices are attached to a board from which bait is dangling. The sharks are also lured towards the board by a trail of minced fish. While this is necessary to ensure that the researchers are able to observe the sharks in a controlled setting, it is not an exact match for the experiences of a swimmer. It should also be noted that people have been attacked by sharks even while wearing repellent devices.

Nonetheless, the results that these experiments provide do clearly illustrate that these devices are not 100% preventative of shark bites. Therefore, whether or not you use these shark deterrents, caution must be exercised to stay safe in the ocean. Although sharks are frequently maligned, and our fears far outweigh their actual risk to our safety, shark attacks have become increasingly frequent.

There are several plausible theories as to why shark attacks have risen. First, there are simply more people. While looking just at the number of shark attacks each year reveals a steady increase, when controlling for total global population, the numbers stay relatively flat. Therefore, more dangerous encounters with sharks could simply be a product of more people entering their habitat. Other possibilities include climate change, with rising water temperatures and heavier rainfall bringing sharks further inland. Just keep in mind that when you enter the water, you are a guest in the shark's home.