Do shark repellents work?Science communicator
We share the same seas as sharks.
It’s a fact: every time you enter the ocean, you’re entering the home of numerous shark species. Most of them pose absolutely no threat to humans. But a few species have been known to (very rarely!) bite humans – the white, tiger and bull sharks. Our fascination with sharks means that these attacks get a huge amount of attention. This can make them seem a lot more common than they really are.
Most of the time, shark–human interactions are safe and often go unnoticed.
With the ever-increasing use of drones, more and more footage showing surfers or swimmers in close proximity to sharks is coming to light. This may seem scary, but it actually shows how common it is to be close to sharks. There’s less than one attack per million people per year and roughly 15% of these result in a fatality (about six people per year die from shark attacks globally). When it comes down to it, sharks aren’t all that interested in attacking us.
But why take a risk when you might not need to?
Even so, it’s good to be prepared. You wouldn’t head into bear territory without taking precautions! Shark attacks have been slowly on the rise since the 1980s. This is due in part to there simply being more people spending time in the water, doing sports like swimming, surfing and diving. Climate change and variations in the amount and location of shark prey may also be partly responsible for the increase in the number of shark attacks. In North Carolina, there’s evidence that bull sharks are expanding their nursery habitat in response to increasing water temperature, which could increase their interactions with humans. And around the Indian Ocean island of Réunion shark attacks have been found to change with the seasons.
We all want to feel safe when we’re in the ocean. This means there’s an increasing market for shark repellents, which aim to prevent sharks from attacking. These repellents are mainly used by surfers, who are most vulnerable to shark attacks. They may make you feel secure from sharks, but they aren’t always cheap. And do they actually make any difference? Unfortunately, most of the manufacturers’ claims of effectiveness are based on theory, not on proper scientific testing. So what is the theory? And what’s the latest scientific evidence saying about whether shark repellents work?
Shedding light on the most common type of repellent: ESDs
An ESD is an electric shark deterrent. It’s the most common type of shark repellent on the market – but not all ESDs are the same! They rely on the electro-sensory system of sharks. Basically, a shark has lots of tiny electro-receptors all over its head. These are called ampullae of Lorenzini and they pick up tiny electrical signals. One of the main reasons that sharks have them is to help them find prey at close range. It makes sense, then, that a species like the bull shark, which relies on this sense to find food, has lots of these electro-receptors, whereas white sharks, which are visual predators, and tiger sharks, which are scavengers, typically don’t have as many.
ESDs aim to overwhelm a shark’s electro-sensory system. They emit electrical pulses (each one does so in a different way) that are supposed to repel the shark. So far, ESDs have been the most effective type of personal shark repellent.
Great, but will they really prevent a shark attack?
Well, that depends. A study by Save Our Seas Foundation Project Leader Dr Charlie Huveneers and colleagues in 2018 aimed to find out. They looked at five different types of the most popular deterrents and whether they actually prevented white sharks from taking bait. The deterrents were Ocean Guardian Freedom + Surf, Rpela, SharkBanz bracelet, SharkBanz surf leash and Chillax Wax. Not all of these are ESDs – the two SharkBanz products rely on magnets and Chillax Wax relies on a shark’s sense of smell.
Only one device, Ocean Guardian Freedom + Surf, had any significant effect on shark behaviour. When the device was active, the percentage of bait taken dropped from 96% (with no repellent) to 40%. The distance of white sharks from the board also increased, from 1.6m (5ft) with no repellent to 2.6m (8ft 6in) when the Freedom + Surf was active. The other four deterrents had limited to no effect on white sharks – even the other ESD (the Rpela)! And it’s worth noting that even when the most effective device was active, white sharks still took the bait 40% of the time… It’s not just how effective the repellent is, but also how hungry an individual shark is.
Other shark repellents that have been proposed include using the smell of dead sharks to deter live sharks from the area, which seems to show some promise – at least, when it comes to Caribbean reef sharks and blacknose sharks – according to a study by SharkDefense Technologies in 2014. But this hasn’t been independently scientifically tested since. And they weren’t testing a specific repellent product on the market, but rather the effect of releasing canisters of dead shark essence.
Another relies on shark vision – or really, their lack of vision! It’s thought that sharks are colour blind. Black and white wetsuits play on this, aiming to break up a person’s silhouette and make them less visible to a shark. But again, this is very tricky to test scientifically. The theory certainly makes sense and anecdotal evidence from a manufacturer of such wetsuits in 2013 would appear to support it. But no robust scientific studies have taken place since then to test the products, so there’s no guarantee that they are effective in preventing sharks from making an attack.
What about other shark species?
Since 2018, scientific studies testing the true effectiveness of shark repellents have been picking up pace. Previously, research has focused mainly on white sharks. But these aren’t the only sharks that are potentially dangerous to humans. A study published in 2020 aimed to discover whether deterrents were effective at repelling bull sharks. They tested five different ESDs: E-Shark Force, NoShark, Rpela v2, Freedom + Surf and Freedom + Surf-Shortboard.
Again, Freedom + Surf was the most effective repellent. When active, it reduced the percentage of bait taken by 42.3%. The Rpela v2 (an updated version after the original was found not to work against white sharks!) and Freedom + Surf-Shortboard both affected shark behaviour too, but they only reduced the amount of bait taken by 16.5% and 16.2%. They reduce the risk, but not by much!
How come the other ESDs didn’t work?
Aren’t they the most effective type of personal repellent? Even ESDs aren’t all the same. The E-Shark Force and NoShark are both repellents that are worn around the ankle or wrist. Another type of electric ankle shark deterrent, the Electronic Shark Defence System (ESDS), has been tested on white sharks. Again, it didn’t have any meaningful effect on shark behaviour. It’s likely that how effective an ESD is depends on where the electrodes are on the device and the strength of the electric field it emits. These types of ESDs just don’t cut it!
The verdict on shark repellents
Not all shark repellents are the same and no repellent is guaranteed to prevent a shark attack. The most effective personal repellent currently on the market is the Freedom + Surf, which has been shown to repel both white sharks and bull sharks. But even so, it only reduces your risk of being bitten by about 60% – and the sharks may still come close! Is it worth it? Especially when the risk of attack is so low already?
Despite the low risk, being bitten by a shark is not something you want to happen. A recent study looked at how many people in Australia could avoid being bitten by sharks if they wear personal electronic deterrents. If all people entering the ocean used the devices, up to 1,063 people could avoid being bitten across Australia by 2066! It’s not just bad news for the person when a shark attack happens – it’s bad news for sharks. Media portrayal of sharks as vicious and deadly animals is wrong and can harm conservation efforts seeking to protect these threatened species. It’s in the best interests of all concerned to prevent these types of shark encounter.
Apart from repellents, how else can we reduce risk?
Lots of research is being done to try to protect people from sharks – and sharks from people. Currently, control measures like large-mesh nets and drumlines are used to prevent sharks from coming close to people at some popular swimming and surfing spots. But these are lethal to sharks and they also kill non-target species like turtles and dolphins. Recently, a new shark fishing device called the Shark-Management-Alert-in-Real-Time (SMART) drumline was invented. Fishers are alerted in almost real time when a shark is caught so that it can be released alive (with an 86.9% success rate).
New technologies like this could play a part in reducing the risk of shark attacks in the future, without harming sharks. Is your local area a hotspot for sharks? If so, check out whether there are any shark detection schemes around. Organisations like Shark Spotters look out for sharks and warn ocean-users in real time of their presence. As drones become more common, it’s likely that these could also play a role in increasing the detection of sharks near humans and could help us to reduce the risk of attacks. Save Our Seas Foundation Project Leader Kye Adams is investigating this and looking to improve aerial approaches to detecting sharks through Project AIRSHIP.
There are also ways to reduce the injury from bites.
Fabrics that minimise injuries also exist, like the Ocean Guardian Scuba7 and Kevlar material. In another recent study on blacktip reef sharks, the Scuba7 material reduced the amount of bait taken by 67%. Neoprene with Kevlar also reduced the risk of serious injury by reducing the size and number of punctures from shark bites. So if you’re frequently diving in an area where shark attacks are known, this is something you could consider.
Take-home messages – do shark repellents work?
Yes and no. If you’re able to purchase a shark repellent, electric shark deterrents (ESDs) are your best bet, in particular the Ocean Guardian Freedom + Surf (at the time of writing). Not a surfer? There are also fabrics you can wear, like neoprene with Kevlar, that can protect you. But none of these products are perfect.
Remember, shark attacks are incredibly rare – and fatalities even more so. Nevertheless, if you’re in an area where sharks are known to occur, it’s best to be prepared.
There are other ways you can prepare yourself. Find out whether there’s a scheme like Shark Spotters near you that alerts ocean-users to the presence of sharks. Or are there particular times or seasons when shark attacks are more likely? Avoiding these will reduce the risk (such as in California).
Research is ongoing and technologies are improving to reduce the risk of negative shark encounters, especially as the risk is increasing. Remember to follow the science, not the fancy branding and claims of effectiveness, when thinking about what personal protection measures to take!
A. R. G. Gauthier, et al., 2020, Variable response to electric shark deterrents in bull sharks.
Charlie Huveneers, et al., 2018, Effectiveness of five personal shark-bite deterrents for surfers.
Madeline Thiele, et al., 2020, Response of blacktip reef sharks to shark bite mitigation products
Channing A. Egeberg, et al., 2019, Not all electric shark deterrents are made equal: Effects of a commercial electric anklet deterrent on white shark behaviour
Corey J. A. Bradshaw, et al., 2021, Predicting potential future reduction in shark bites on people
Charles W. Bangley, et al., 2018, Increased abundance and nursery habitat use of the bull shark in response to a changing environment in a warm-temperate estuary