Threatened Murray crayfish have been hitching a ride down the Murray River with scientists, who hope the relocation program will speed up the recovery of the species in southern inland New South Wales.

Over the past two years, 400 of the spiny creatures have been boxed into large eskies, before they have been driven 200 kilometres by car to be released back into the river further downstream.

Murray crays, the second-largest freshwater crayfish in the world, were already in decline when floods in 2010-11 saw thousands of the crustaceans walk out of the water due to 'blackwater' or a lack of oxygen, and die in the extreme heat.

Trevor Daly, senior fisheries manager for threatened species at the NSW Department of Primary Industries, said the crays had fared better in some parts of the Murray River than others, and were listed as vulnerable.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 34 seconds 1 m 34 s Scientists, fishers work together to bolster Murray cray populations ( Off Track: Ann Jones and Corey Hague (2017) )

"The upper reaches of the Murray, they didn't do too bad in those events and they're still holding their own, so we've generally been moving them down around the Echuca Moama area [near the Victorian border].

"[We] don't want to be too specific about it obviously, because you can't harvest in that area, and there's only a very limited area and season when you can take them in parts of the Murray and parts of the Murrumbidgee."

Slow coach crays given a faster ride

Dr Daly said while the crays had experienced some natural recovery since 2010-11, it was not easy to recolonise an area.

He said the crays walked very slowly, and tended to disperse their eggs within a localised area.

"What we're doing to try to speed up their natural recovery is to pick them up and drive them down the road and let them go," Dr Daly said.

An adult female Murray cray with eggs is released back into the Murray River. ( Supplied: NSW DPI )

Female Murray crays can take up to 10 years to reach sexual maturity and males take four years, so Dr Daly said without intervention, it could take much longer for crays to return to the Echuca Moama area.

"I think to get them back, assuming there are no more natural events that could cause a decline, it probably will take more than 10 years.

"By doing these translocations, we're hoping to speed it up, because if we just left it to nature, it would probably take 20, 30 or 40 years for those Murray crayfish to walk 100 to 200km downstream, which is effectively what we did.

"We picked them up and drove them 200km or so downstream," he said.

Claws tied to prevent road-trip fights

Dr Daly said the crustaceans needed special care so they did not kill each other en route, and their distinctive white claws were banded up to prevent fights.

He said the crays were no worse the wear for the trip.

"When they're close to each other they'll attack each other and to stop that happening we've had to band their claws up and then put them in these eskies.

Murray crayfish has its claws tied up before being relocated. ( Supplied: NSW DPI Fisheries )

"Then we basically drove them down the road and reversed the process, took the bands off, took them out in boats and re-released them back into the river.

"Obviously after their car ride they were quite happy to get back into the river, but we didn't have any losses.

"There was no problem with them and they didn't seem to mind it at all, because they can survive out of water."

Illegal harvesting

Illegal harvesting of Murray crayfish is an ongoing problem in NSW.

Dr Daly said fisheries officers often caught people not following the rules.

He said the fishing restrictions aimed to strike a balance to ensure the crayfish could slowly recover while still allowing some recreational catch, but he warned that without progress, a total ban on fishing might be imposed.

Map of NSW showing areas where Murray crayfish fishing is allowed. ( Supplied: NSW DPI )

"If people don't follow the rules and the species continues to decline, then it could be made totally protected in the future with no catch allowed

"We ask that people do the right thing so this species is still around for future generations."

Australian National University researcher Mae Noble studied the species decline in the Murrumbidgee system, a major tributary of the Murray River, in 2016.

She expressed concern then that Murray crayfish could be fished out of the rivers.

"I've heard that they're quite tasty, but for me it's kind of like eating a tiger or something very endangered.

"I think we need to move away from eating them and just help them as healthy little individuals, helping us keep our streams healthy."

The crayfish are also an important food source for native species like platypus and water birds.

Funding runs out

Loading...

Dr Daly said more funding was needed to continue the relocation program and extend it to the Murrumbidgee River.

"We've been getting funding from the Recreational Fishing Trust for this, they've been very good with both funding some of the monitoring studies and the translocation, so we thank Recreational Fishing Trust for that.

"We're now putting in a proposal to ask them to fund a few more years of that translocation and part of the new proposal is to start doing the work in the Murrumbidgee as well."

Dr Daly said landowners on waterways could help provide Murray cray with habitat by ensuring snags were left in the water and that there was native vegetation on the banks.

Fishers could help the species' recovery by recording sightings and not taking crays outside the limited open season.