Opera house traps, named for their resemblance to the sails of the iconic Sydney structure, have been illegal on the east coast of NSW for nearly 20 years and totally banned across the state since April last year.

The traps lure yabbies into the wire mesh structure with bait.

Designed to provide no way out for the yabbies, the traps, in turn, have a deadly effect on any air-breathing aquatic wildlife including platypuses, rakali and turtles, which are attracted by the caught crustaceans.

'Net full of death':

That was the scene Dangarra Landcare volunteer Piers Hammick confronted in Dorrigo earlier this month, finding the platypuses and rakali in what he described as a "Net full of death".

"It only takes three minutes or so before a platypus or rakali can run out of air and drown in a trap."

Earlier this year, a platypus was also found dead in a home-made opera house style trap at Logans Crossing, inland from Port Macquarie.

Platypus Conservancy Foundation biologist Geoff Williams says "There is no excuse these days for people using these death traps" given the availability of open-top alternatives that are wildlife-friendly.

"The ban has been very effective in reducing deaths but that's why this case [in Dorrigo] is particularly distressing.

"A year down the track we are finding that people are still using them and that they take this incredibly heavy toll on platypus populations."

Platypus numbers dwindling: 

Mr Williams said the impact of opera house traps and other types of enclosed nets is well documented, with a Victorian study tracking platypus mortality from 1980 to 2009 finding 56 per cent of deaths were caused by drowning in illegal nets.

"If you knock four platypus out of the population at once then you can potentially knock a big hole in the population," Mr Williams said.

"If you knock out breeding females or juveniles then you quickly make a dent that adds to this slow slide in platypus numbers."

Mr Williams said platypuses are also frequently found dead strangled by hair ties, elastic bands, released balloons, other fishing gear and general plastic pollution.

"Platypus populations throughout NSW are under pressure ... and we need to make sure they have time to bounce back after events like fires and floods."

Concern some retailers still stocking illegal traps:

While the use of opera house traps is outlawed in NSW, Victoria and Tasmania, other states have been slower off the mark, with several fishing gear suppliers still selling the deadly devices.

Mr Williams says it is "Extremely disappointing" some retailers continue to advertise them as legal throughout Australia.

"It is a peculiarity in our laws that while using the traps is illegal, selling the traps isn't."

Penalties for using the traps in NSW range from a $500 infringement fine to 12 months' imprisonment for a second or subsequent offence.

Ramping up preventative measures:

Jim Harnwell, fisheries program leader at the NSW Department of Primary Industries (DPI), said keen yabby fishers, particularly on the state's east coast, should know better given the traps have been illegal for nearly two decades.

"They were a very common device, readily available and quite an effective yabby catching tool, so a lot of people probably have them lying around in the back shed," Mr Harnwell said.

Last year the DPI gave away 5,000 open-top pyramid-style traps to help with the transition away from the opera house traps and is now rolling out new warning messages to educate people about the ban.

"When we do have an incident of someone using one of these traps our compliance team will go in and put up one of these signs, so if the culprit goes back they can see the sign and realise they're not allowed to use them."

The department is also encouraging people to "Actively fish" and not leave yabby nets sitting in waterways for long periods of time, so they can potentially find and release any unwanted bycatch.

Story By | Alexandra Jones