There’s good news and bad news for ocean swimmers who’ve forked out several thousand rand for an Australian-made personal protective device to ward off sharks – it works… but only some of the time.

And at least one shark was encouraged by the device.

The Shark Shield Freedom7 electric deterrent, also marketed and sold in SA, is one of the most popular of its kind, but until recently its effectiveness had never been subject to independent scientific testing.

Now a comprehensive study has been done by Australian scientists and SA research colleagues who did some of the work in False Bay.

Led by the South Australian Research and Development Institute (Sardi), it involved 116 trials using a static bait at the Neptune Islands in South Australia, and 189 trials that involved towing a seal decoy near Seal Island.

The results showed that while the deterrent had an effect on the behaviour of white sharks, it did not deter or repel them in all situations and nor did it repel all individual sharks.

“While it was expected that the deterrent would dissuade white sharks from taking a static bait, the ability of the deterrent to stop a white shark in a targeted predatory behaviour was unknown.”

One particular shark actually seemed to be encouraged by the device – it took the bait four times faster when the deterrent was activated.

The proportion of baits taken during static bait trials was not affected by the deterrent. However, the deterrent increased the time it took to take a static bait, and increased the number of interactions on each approach.

During the dynamic seal decoy tows, no breaches and only two surface interactions were observed when the deterrent was activated, compared to 16 breaches and 27 surface interactions when the deterrent was not activated. Breaches are common predatory behaviour.

“The results showed that the deterrent had an effect on the behaviour of white sharks, but did not deter or repel them in all situations.

“Future studies should focus on testing the effect of deterrents less than 2m from the bait, in locations not frequented by cage-diving operators, and on other potentially dangerous sharks, such as tiger sharks and bull sharks,” the study concluded.

One of the South Africans involved in the study was Dr Alison Kock, research manager for the city’s Shark Spotters organisation.

She told the Cape Argus that

she and her fellow shark researchers were frequently asked whether the shark shield worked and how effective it was.

“And up until now, there’s been limited information available to make informed comment. This study provides us with a greater insight into the deterrent’s effect on white shark behaviour,” she said.

“The combined results of the study indicate that while the risk of an attack may be reduced wearing a shark shield, the shields failed to repel great whites in all cases.” - Cape Argus