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Personal Deterrents Can Reduce the Risk of Shark Bites

Credit: Andrew Fox / Rodney Fox Shark Expeditions

Credit: Andrew Fox / Rodney Fox Shark Expeditions

By Charlie Huveneers & Corey J. A. Bradshaw

A study tests how effectively commercial shark deterrents reduce the risk of shark bites.

Many things might explain why the number of shark bites appear to be increasing. However, the infrequent occurrence of such events makes it nearly impossible to determine why. Recently, an atypically high rate of shark bites occurred in Western Australia in 2010-2011 and on the north coast of New South Wales in 2015-2016. These highly publicised events — often sensationalised in both traditional and social media — have pressured governments to implement new measures to reduce the risk of shark bites.

The rising pressure to do something to reduce shark bites has prompted the recent development or commercial release of many new personal shark deterrents. Yet, most of these devices lack any rigorous scientific assessment of their effectiveness, meaning that some manufacturers have made unfounded claims about how much their devices dissuade sharks from attacking humans.

However, if a particular type of commercially available shark deterrent happens to be less effective (or completely ineffective) as advertised, it can give users a false sense of security, potentially encouraging some to put themselves at greater risk than is necessary. For example, some surfers and spearfishers probably ignore other mitigation measures, such as beach closures, because they ‘feel safe’ when wearing these products.

Given the lack of scientific evidence about the efficacy of many commercially available deterrents, we designed an experimental study to test how much shark deterrents reduce the risk of shark bites. We spent 18 days at the largest-known aggregation of adult white sharks (Carcharodon carcharias) in Australia — the Neptune Islands Marine Park— to test if the Ocean Guardian Freedom+ Surf (previously known as ‘Shark Shield’), Rpela, SharkBanz band, SharkBanz leash, and Chillax Wax could reduce the risk of shark bites by comparing the percentage of baits taken, time to take the bait, number of passes, distance to the bait, and whether a shark reaction could be observed.

Illustration of the board set-up (120 × 30 cm) with the five deterrents tested. Illustration by René Campbell, Flinders University)

During our 300 trials, 44 different white sharks interacted with the deterrents for a total of 1413 passes. The effectiveness of the deterrents was highly variable. The Freedom+ Surf affected shark behaviour the most, resulting in the most reactions and reducing the percentage of bait taken from 96% (relative to the control board) to 40%.

The average distance of white sharks to the surf board was also affected, with sharks remaining further away from the board when the Freedom Surf+was active (2.6 m vs. 1.6 m). We found that the other deterrents had limited or no measurable effect on white sharks.

Surprisingly, the other deterrent based on electric field (Rpela) did not have the same effect as the Freedom+ Surf. While both devices are designed to use electric fields to deter sharks, they differ in their field characteristics. We were unable to identify which characteristics caused Rpela to be less effective than the Freedom+ Surf, because the differences in field propagation, pulse type, duration, or frequency are unknown. However, the discrepancy in shark responses between the two products shows the complexity of electric deterrents and the need to ensure that adequate testing is done for all new products before commercial release.

Shark deterrent testing.Illustration by René Campbell, Flinders University

Our study is therefore the first comprehensive experiment to show that many ‘deterrents’ do not perform as intended, thus potentially putting users at greater risk by creating a false sense of security. Manufacturers should consider our findings to assess the suitability of their products, and gauge whether changes are required to ensure that their products perform as advertised.

Our results will allow people to make appropriate decisions about the use and suitability of these five products. The Western Australia government has supported a ‘shark deterrent rebate’ programme for the Freedom7 since 2017, so based our new findings, they intend to add the Freedom+ Surf (i.e., the device that reduced the probability of a shark bite the most) their programme.

Of course, more testing is required in different locations, for different shark species, and possibly in different circumstances, before the universal effectiveness of any proclaimed shark deterrent can be quantified completely. Nonetheless, our study identified one product that reduced the likelihood of an interaction with white sharks by more than 50% — and identified some that did not.

Charlie Huveneers & Corey Bradshaw, Flinders University