A study of the effectiveness of electronic shields to prevent shark attacks has found they cannot always be relied on.
Researchers found the devices can deter some great white sharks but they do not always work.
Recreational diver Steve Reynolds invested in a shark shield seven years ago as an insurance policy.
"The theory is that if a shark is snooping around, it senses the device then it'll leave you alone," he said.
The device sends out an electronic pulse which is said to repel sharks.
Research was commissioned by SafeWork SA to assess the effectiveness of the devices for commercial fishing crews.
Researchers used static tuna baits off Neptune Island in South Australia and seal decoys in South Africa to measure whether sharks were deterred by the electrical pulses.
No difference
Researcher Charlie Huveneers wrote up the results.
"In South Australia with the static bait, we did not find any differences in the proportion of bait being consumed by white sharks whether the shield was turned on or off," he said.
"There are situations where the white sharks were still capable of getting very close to the shark shield, within half a metre, and was still capable of consuming a bait.
In South Africa, researchers found the shield was more effective in deterring an attack.
Researchers have concluded that while the risk of an attack may be reduced, the shields failed to repel great whites in all cases.
Shark shield manufacturers could not be contacted for comment.
The report recommends more research into other shark species and tests in areas without tuna baiting which is done for tourist cage-diving to see sharks.