Murray crayfish are on the comeback trail in twin towns

October 10, 2017

Two of the released Murray Crayfish. Image:Supplied

THE Murray crayfish is back.

Not in big numbers yet but researchers have made a trial introduction of 200 crays to see how they cope after the millennium drought and floods devastated local numbers.

The crays were quietly released in July and Nature Glenelg Trust researcher Nick Whiterod said it was looking good as the crays have shown a high survival rate in the river.

“We’re reintroducing them back into a stretch of water that was impacted by a significant black water event, and the population just hadn’t really been bouncing back at all,” he said.

“The black water event lasted for about six months in certain areas, and it affected an 1800km stretch along the Murray.

“Our most recent sample was last Friday and we detected the species, so it’s good to see that they’re hanging around.

“There have been a few pockets in and around Echuca, upstream towards Cohuna as well, but nothing like what the numbers were beforehand.

‘‘Once the flooding came a lot of the floodplain areas went under and some of those hadn’t been inundated for as many as 20 years,’’ Dr Whiterod said.

‘‘Leaf litter that had been building up on the bank had accumulated and then when those big floods occurred, microbes started breaking down the leaf litter and stripping oxygen from the water.

‘‘Essentially that’s what black water is all about — it’s water that comes off the flood plain [with] low oxygen levels or concentrations and it comes back into the main channel and lowers the oxygen concentration.’’

While Dr Whiterod was confident the reintroductions would bring population numbers up, he said this was only the beginning for the conservation efforts.

“We placed about 200 back in the river, but we feel that it wasn’t enough so that’s why we’ve planned to do it again,” he said

“Fisheries closed off the section downstream from Tocumwal about five years ago, and it’s not likely to open back up, simply because the population hasn’t been able to get back to the previous numbers.”

“A major problem is that they’re slow growing and long living, so they’re not really in a rush breeding wise, and that can affect our repopulation programs too as we can’t make too much of an impact on the population where we’re getting them from.”

While it could be argued there have been attempts at reintroductions before, this is the only official one.

“The translocation we’re doing is in addition to some other programs but something like this hasn’t been done in almost a century, not officially anyway,” he said.

“There have been some people trying to do it themselves, but generally the genetic diversity is unknown and there needs to be a pretty sizeable population to make sure they survive. The research we’ve done gives the best chance at success.”

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