Unusual shark deterrent devices you can buy or make
THE rise in shark attacks has seen a global boom in shark repellent devices.
But the science for some (not all) of these devices is more speculative than proven.
The repellents listed below may give you peace of mind, but even the manufacturer will advise you not to trust your life with them.
1. Personal shark cages
This invention is not for sale.
It's just a wacky invention which one North Carolina couple decided to put together to ensure they could swim in peace.
The waters around the Carolinas are notorious for bull sharks and there has been an unprecedented rise in shark bites.
It turns out it was all a bit of a joke as the couple had made the cage out of PVC and spray painted it to resemble steel.
3. Shark repelling wetsuits
The theory goes that some animals in the sea are so poisonous that sharks have an evolved sense not to eat them.
So it is with the banded sea snake, the most venemous snake in the world.
The wetsuit is coloured with black and white stripes and voila, the surfer becomes a human sea snake never to be attacked.
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But there is still no scientific consensus on whether this actually repels sharks.
3. Lionfish rashies
Florida website BoatsToGo.com sells this rash vest as a visual deterrent to shark attacks in Florida's subtropical waters, which are frequented by bull sharks and tiger sharks.
It is coloured with the design of a lionfish, a toxic pest fish in that part of the world's oceans.
The website proclaims the rashie cools the wearer off on a hot day, provides sun protection, "and may even reduce your chance of being attacked by a shark!!!".
It says it "can't guarantee" the product will make you "totally invisible to sharks", but there is a "good probability" that the "already slim chance of being bitten by this predator might become even slimmer."
But on environmental website Treehugger.com, reviewer Jaymi Heimbuch pointed out that "lionfish don't usually hang out on surfboards", and that sharks looking for prey are looking for "size shape and movement" not necessarily colour.
4. Shark spray
The Anti Shark 100 shark repellent spray was developed around the understanding that sharks hate the smell of their own dead, much as humans do.
It's a liquid extract made from dead sharks.
It sounds whacky, but this is scientifically proven stuff.
According to the company's website, the product was tested in a five year field trial and "proved to repel two species of sharks 100% of the time within one minute of local dispersion of our product".
The findings were published in the scientific journal Ocean & Coastal Management, here.
As such it is used by divers and spearfishers.
The problematic issue is that in the one minute of the dispersion to effect the victim has already been bitten.
Shark bite victims who are swimming or surfing rarely know a shark is coming.
Nor would it be immediately practical for surfers to carry a spray can.
5. Painting your board black
Painting the underside of surfboards (and the fins) black is an increasing topic of discussion among surfers.
If you are looking to save money, it's the one option of all the above that is virtually free.
The idea is that sharks are colour blind and see the world in shades of grey, so a darker object is less likely to attract them.
This theory is popular with some fishermen who equate shark attacks on humans with light coloured surf boards as just like a big fish attacking a brightly coloured lure.
Notably Mick Fanning opted to "paint it black" after his well-publicised shark encounter at Jeffreys Bay in 2015.
But according to consumer website Choice, which authored a comprehensive review of shark repellent devices and their merits, there was a glaring Achilles heel in this thinking.
"When viewed from directly below, a surfboard will be seen as a dark silhouette, regardless of its colour."
But it could be "worth a try".