Shark nets are back in the water in NSW, a day after a surfer was mauled north of Sydney, but conservationists say they are wildlife killing machines that don’t protect humans.

Every year, on September 1, about 50 shark nets are reinstalled at beaches up and down the NSW coast and stay there until the end of April.

Queensland has 27 nets along its coastline, but they stay in the water year round.

Both state governments say the nets are an important part of their shark control efforts but conservationists and academics say they are nothing more than a feel-good gesture for a fearful public, and take a horrific toll on marine life.

Earlier this year, the NSW government revealed that three target shark species accounted for just 13.5 per cent of everything trapped in the state’s nets last season.

Threatened species accounted for 22 per cent of the 376 animals caught, and included critically endangered grey nurse sharks, vulnerable green turtles, endangered leatherback turtles, and endangered loggerhead turtles.

Queensland has already had 10 whale entanglement incidents so far this migration season.

NSW Agriculture Minister Dugald Saunders has said his government will be “ramping up” all shark mitigation strategies to keep people safe this summer and has called the meshing program “great” and successful.

Queensland Fisheries Minister Mark Furner has consistently said “human life comes first” and no changes will be made unless he’s convinced it’s safe.

Humane Society marine biologist Lawrence Chlebeck said both governments were ignoring evidence that showed shark nets, and baited drum lines used in both states, did not protect swimmers.

He said their had been almost 40 shark bites at “so-called protected” NSW beaches and about double that at protected sites in Queensland.

University of Sydney political scientist Dr Christopher Pepin-Neff, who has worked on the shark nets issue for 16 years, has said nets don’t work and they are a deception perpetuated by politicians.

Protests were held on Thursday at Manly beach in Sydney, in Byron Bay and on the Gold Coast as the NSW shark nets went back into the water.

They were planned before a teenager was bitten on the hand at North Avoca Beach, on the NSW Central Coast, about 7am on Wednesday. He’s recovering.

Baited drum lines had been set in the area about the same time.

Mr Chlebeck said the drum lines didn’t help the teenager and nets wouldn’t have either, had they been in the water.

“That equipment does not form a barrier and sharks can easily move inside the nets, above and around as well,” he said.

“Drum lines are ineffective at reducing risk. If anything they could potentially be attracting sharks inshore. I’m not saying that’s what happened on this occasion, but it’s very possible.”

Federal Greens Senator Peter Whish-Wilson said shark nets and drum lines were a spectacular failure when it came to human safety and took a horrifying toll on non-target species.

He wants federal Environment Minister Tanya Plibersek to end the exemptions shark nets have from federal environmental laws.

“They don’t make beaches safe. At the very least she should ask NSW and Queensland to show just cause for continuing to use them,” he said.

– AAP