A fatal shark attack at a popular northern Sydney beach has reignited debate over shark nets.
Despite being installed along the Northern Beaches just weeks ago, experts say nets do not always stop the ocean’s biggest predators.
Mercury Psillakis, who was killed by a shark at Long Reef Beach on Saturday, was in the water where a shark net had been installed at nearby Dee Why as part of a rollout that included 50 other beaches from Newcastle to Wollongong.
On Saturday an experienced surfer was killed by a shark at Long Reef Beach. (ABC News: Liam Patrick)
What do shark nets actually do？
Shark nets are typically a 150-metre-long netting system, which sits at the top of water but are open at the bottom and to the sides.
Christopher Pepin-Neff works at Sydney University and has researched shark nets for almost 20 years.
“They’re these gill nets that are set in front of the swimming area in front of the flags, and they’re stable there. They’re sort of anchored there,” they said.
Contrary to popular belief, the nets do not completely block fish from the open ocean.
Cottesloe Beach in Western Australia has a shark barrier. (Google Maps/Town of Cottesloe)
This is largely due to the fact large swells, currents and sea debris can wash the netting away.
“Mother Nature — we build things in the ocean — and Mother Nature blows it down,” he said.
Cottesloe Beach in Western Australia has a shark barrier. Adelaide also has several full enclosures that are in the harbour or at what experts call “low energy beaches”, where there aren’t as big waves or a lot of seaweed.
Why do shark nets prevent bull sharks but not white sharks？
According to Professor Pepin-Neff shark nets do two different things for two different types of sharks.
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“For instance, white shark, shark nets are not effective, and there’s no evidence to support that they would reduce the risk of a shark bite, particularly because great white sharks are pelagic [open ocean swimming fish],” they said.
“But shark nets for bull sharks, for instance, are more effective because bull sharks are not pelagic, they’re more residential.”
Has there been an attempt to completely seal off a beach？
Attempts to seal off Coogee Beach in 1929 failed spectacularly.
“This was the first shark net. They put it on a wire, hung it in front of Coogee Beach,” Professor Pepin-Neff said.
“At the opening ceremony, when they went to cut the ribbon, a stiff wave came, snapped the wire, and it washed ashore and everyone freaked out.”
Can the nets attract sharks？
There is evidence that other marine life get caught in shark nets. (Supplied: Sea Shepherd Australia)
Professor Pepin-Neff argues there is more evidence that shark nets attract sharks toward local beaches.
“Sharks are attracted to the vibrations and sounds underwater of struggling fish. And the nets are just a regular fishing net.
“The shark would probably need to already be in the general vicinity. It doesn’t get a shark from six miles away.
“We know from evidence from DPI [Department of Primary Industries] there was a GIPA [Government Information Public Access] on photos of the fish, rays, dolphins and sharks that were taken out of the nets, and they all have giant shark bites in them.”
Professor Pepin-Neffwarns said a safer beach is a beach where you educate the public and let them know about the risks.
Are there other shark prevention methods？
More than 300 smart drum lines are deployed daily between Merimbula on the South Coast to Kingscliff. (Supplied: DPI)
Research scientist Paul Butcher works for the Department of Primary Industries and Regional Development and is involved in several shark prevention programs.
“We have 305 smart drum lines deployed daily between Merimbula on the South Coast to Kingscliff on the North Coast,” he said.
“Each time we catch a white tiger or bull shark, it’s tagged with an acoustic tag.
“That acoustic tag is then picked up by any of the 37 tag shark listing stations along the New South Wales Coast, and those big yellow boys, which are more often in front of surf clubs along the New South Wales Coast East Coast then detect those sharks as they travel along the coast.”
Why didn’t it prevent Saturday’s fatal attack？
Not every shark can be monitored or caught every time it swims past the bait stations.
“We have around 1,500 white sharks, 700 tiger sharks and 230 bull sharks that are that are tagged, so they’re just a fraction of the total population,” Dr Butcher said.
Just a fraction of the shark population is tagged. (Supplied: DPI)
Preventing future shark attacks requires what Mr Butcher labels as a “suite of everything”.
“There’s no sort of golden ticket here in terms of reducing shark bites.”
He said prevention requires a combination of alternative options such as shark nets, drum lines, acoustic tags and drones.
“Shark bites are really rare, so being able to test which technology is better than the other is really hard to do because it is a rare event.”