A trial of shark nets off the north coast of NSW could last for another two years after the Turnbull government waived environment protections despite its own departmental advice.
Environment and Energy Minister Josh Frydenberg announced on Thursday the exemption for the meshing trial from the Environment Protection and Biodiversity Conservation Act will be extended to the end of October 2019.
In a statement, Mr Frydenberg said the extension was "due to the risk to human life from shark interactions", and to enable the continuation of research into shark mitigation measures.
"The trials will continue to assess the catch of target sharks and bycatch of the nets against SMART drumlines used in the trial area," he said, adding the NSW government would use further trials to test ways to minimise the capture and mortality of non-target animals.
But the Environment Department's own advice noted "it is possible that historical meshing programs have contributed to a decrease in the size of the white shark population", referring to one of the target species in the nets program.
Similarly, the survival of the grey nurse shark - a non-targeted but endangered animal that is also being caught in shark nets - is undermined by meshing. Such netting "could contribute to impacts that may disrupt the breeding cycle of the species [and] may lead to a long-term decrease", the advice noted.
Other species, such as manta rays, loggerhead and green turtles, were also likely to be affected by the nets.
"The Environment Department has clearly told Josh Frydenberg that the first so-called netting trial was a failure, but he has gone and given another free pass to the NSW government to continue it anyway," Peter Whish-Wilson, the Greens ocean spokesman, said.
"Any shark net trial should have been subject to a full approval process and Frydenberg granting a 'national interest' exemption - a loophole put in place for war and natural disasters - makes a mockery of Australia's environmental laws," he said.
Marine scientists generally discount the value of shark nets in promoting swimmer safety.
The half-dozen north coast nets, for instance, cover only about 600 metres of some 32 kilometres of coastline, and sit between the surface and the seabed - allowing sharks around, under or over the mesh. Their installation was prompted by a spate of shark bites and several deaths in the region more than two years ago.
Although the nets were supposed to go back into the sea on November 1, Fairfax Media understands the re-introduction of at least one of them has been delayed because of concern they may snag whales.
NSW scientists point to the relative effectiveness of smart drumlines, which typically catch targeted species - whites, bulls and tiger sharks - with lower mortality of the animals and much less unintended bycatch.
Two more drumlines have recently be installed off Kiama and Ulladulla, south of Sydney, with one shark already caught, tagged and released.
Fairfax sought comment from Mr Frydenberg.
The government's shark policy will come under more scrutiny when the Senate inquiry into shark mitigation reconvenes on Tuesday in Canberra, with departmental officials due to give evidence.