It’s summer, the heat’s glimmering off the tarmac, and Australians are flocking to the beach. It’s when we start thinking about big marine predators – and how to prevent a shark attack.
Although shark-human interactions are rare and unlikely events, sharks are often at the back of every surfer’s or swimmer’s mind – and to capitalise on this perceived threat, a range of gadgets claiming to act as shark deterrents have entered the market.
From electrical antennae to smelly surfboard wax, these products often come with a high price tag. If you’re an anxious ocean-goer, you might be wondering: do any of these deterrents actually work? Which ones have been rigorously tested by independent researchers, and just how effective are they?
“It’s really important for people to be aware of what deterrents can but also cannot do,” says Charlie Huveneers, a shark ecologist from Flinders University, South Australia. “Without the right information, how can people make the right decisions?”
Let’s take a look at the science behind these gizmos.
Shark attacks: the facts
- The majority of shark bites are non-fatal; eight people died from them in Australia in 2020. In the same period, 1,106 people died on Australian roads
- Over the past decade, Australia has averaged 20 shark bites per year, up from 6.5 per year in the 1990s
- The frequency of shark bites has been increasing globally since the 1980s
- The primary reason for the long-term increase is not well understood. A combination of factors is likely to blame, including increasing human populations and ocean use
- While some shark populations are growing, across species sharks are declining. There is no clear scientific evidence that the populations of potentially dangerous sharks (tiger sharks, bull sharks and white sharks) are increasing
What types of shark deterrents are on the market?
Deterrents tend to focus on a shark’s senses. One of the most popular types relies on the fact that sharks possess special gel-filled pores on their snouts, able to detect tiny electrical currents from their prey – for example, the heartbeat of a nearby fish. These deterrents use strong electrical pulses to overwhelm a nearby shark’s senses, forcing it to swim away. The pulses are generated by two electrodes, often attached to the underside of a surfboard or worn around the ankle as a long, trailing antenna. The pulse characteristics (for example, strength and frequency) vary between manufacturers, which can affect the deterrent’s efficacy.
Another type of repellent – a magnetic band, worn around the wrist or ankle – claims to work on a similar principle, overwhelming a shark’s electromagnetic senses.
Some deterrents aim to upset a shark’s keen sense of smell. Repellent sprays, for example, mimic the smell of rotting shark meat, while surfboard waxes use a concoction of strong scents to mask a human’s smell.
Other deterrents focus on a shark’s sight and making sure that humans don’t look like prey. Wetsuits and surfboards have been designed to either make a surfer blend into the patterns of the water and sky, thus camouflaging them, or to make them stand out with bright colours unlike prey.
Acoustic shark repellents are also under development, attempting to use sound to scare a shark away – such as the “scream” of their natural predator, the killer whale.
But do any of these products work?
Most of these products have not been tested independently or scientifically, but several scientific studies have quantified their efficacy in the last few years. It’s not easy to study shark behaviour in the lab, so scientists have had to head into the field.
Huveneers has been involved in testing a variety of deterrents across South Australia, South Africa, New Caledonia and French Polynesia.
In a 2018 study in the Neptune Islands in SA – home to one of Australia’s largest aggregations of mature white sharks (Carcharodon carcharias) – Huveneers and team conducted a series of trials to test five popular shark deterrents, including electric-field-based devices, magnetic bands, and surfboard wax.
The team used a mix of fish oil and southern bluefin tuna (Thunnus maccoyii) as bait, tempting sharks towards mock surfboards fitted with the shark deterrents. They watched from a nearby boat, with cameras below the surface.
Overall, they conducted 297 successful trials, watching as 44 great whites interacted with the bait 1,413 times. To see how effective each deterrent was, the scientists measured a variety of different factors: how close the sharks came to the bait, how many times they passed the bait before investigating it, how often they took the bait, and whether or not the shark visibly reacted to the deterrent device.
The results? A bit fishy.
Only some of the products affected the sharks’ behaviours; others seemed to have little to no measurable effect. The best results came from the electric-field-based products, and in particular a product called Freedom + Surf, made by a 20-year-old company based on Sydney’s northern beaches.
“We found that this electric deterrent reduced the risk of a shark bite by around 60%,” Huveneers says.
Not all electric deterrents were equal, however. The position and size of the electrodes producing the electric fields influenced how effective the device was, and so did the type of electric fields being produced.
Many of these devices claim to have been designed to repel smaller and less dangerous sharks, and it seems that this doesn’t translate to curious great whites.
In 2019, a research team looked at whether electric deterrents reduced shark bite risks from another potentially dangerous species, bull sharks (Carcharhinus leucas), in New Caledonia. They tested several of the same devices as the 2018 study, also using a mock surfboard and bait.
The results were varied – again, the Freedom + Surf produced the best results, reducing the number of times a shark took the bait by 42.3%, with other devices causing smaller reductions. But the effectiveness of the deterrents appeared to decrease over time. Previous studies have suggested that when repeatedly exposed to electromagnetic fields, sharks may learn to tolerate them, although other research – including Huveneers’ 2018 study – has not seen similar tolerances.
Crucially, none of the products completely stopped the sharks from taking the bait.
No shark deterrent is guaranteed
Even if a deterrent has 60% efficacy, it’s not foolproof. But testing devices in a transparent, independent, peer-reviewed way allows the public to make informed decisions about not only whether to buy a product, but also when, where and if to go in the water.
“There is currently no silver bullet that will completely stop the risk of shark bites,” Huveneers says – then pauses. “Well, actually this isn’t quite accurate. The two options are: either stay out of the water, or swim in an enclosure.”
He further explains that there are three different ways to reduce shark bites. The first is to simply reduce the times that humans and sharks are in close proximity, which can be achieved via monitoring programs and humans choosing low-risk areas and times to be in the ocean.
But if you’re in the water, there is a risk – however low – of encountering a shark.
The second step is to stop sharks from biting humans, which is where deterrent devices come into play. Finally, the third step is to reduce the injuries sustained from a bite.
In a study conducted in 2020, Huveneers worked with an international research team in French Polynesia to test whether Kevlar-strengthened neoprene was more resistant to shark bites. Kevlar is a strong, lightweight, flexible material that is highly resistant to punctures; it’s currently used for applications such as bulletproof clothing.
The team found that when bitten by blacktip reef sharks (Carcharhinus melanopterus), the Kevlar-neoprene had fewer, smaller and shallower holes when compared to standard neoprene. Another study conducted in 2019 in South Australia had similar results – this time with white sharks.
While this kind of fabric would not stop internal injuries or breaking bones, it could reduce the resultant bleeding. Fatalities from shark bites often stem from blood loss, so reducing this both helps the person bitten and allows emergency services more time to respond to the incident.
Why should these devices be tested?
The logistics of testing shark deterrents in the wild are challenging – locations are often exposed and remote – and expensive, which may be the reason that many devices are not robustly assessed.
But despite the difficulties, testing is critical to provide information to the public – who may be trusting their lives to these devices.
Huveneers is a surfer himself, and he mentions that he’s seen people with ineffective shark deterrents going to high-risk surf spots they wouldn’t usually visit, such as breaks near seal colonies, and even, on one occasion, returning to the water after a shark had been sighted.
“They’re putting themselves at greater risks because they are believing in a product that has been made commercially available,” he says. “However, the tests have shown later on that they are actually not reducing those risks.”
Many argue that since the risk of being bitten is very low, shark deterrents are great for giving people the confidence to get into the water. “But,” Huveneers says, “when a peace of mind leads to people putting themselves at greater risk, I think that becomes an issue.”
To avoid a bite, be SharkSmart
Swim between the flags at patrolled beaches and check signage
Have a buddy and look out for each other
Avoid swimming at dawn or dusk
Reduce risk, avoid schools of bait fish or diving birds
Keep fish waste and food scraps out of the water where people swim
Swim in clear water away from fishers
If you’re a keen beachgoer and you’re wondering if you should invest in a personal shark deterrent, Huveneers has some words of caution.
“Do your research before deciding whether to purchase something,” he says. “There’s a lot of information out there, but my advice would be to find independent scientific information, rather than simply believe claims by manufacturers – unless it’s been validated by science – or opinions from other members of the public.
“There are a lot of opinions out there and some of them can be very convincing – but they’re oftentimes unsubstantiated.”
Originally published by Cosmos as Keeping bites at bay
Lauren Fuge is a science journalist at Cosmos. She holds a BSc in physics from the University of Adelaide and a BA in English and creative writing from Flinders University.
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