It’s been over 10 years since a 5-year moratorium was placed on Murray crayfishing by NSW authorities for our stretch of the Murray River. Sadly, now it seems that Murray cray populations are at risk, not from fishing, but from poor water quality.

Dissolved oxygen has fallen to 0.2 in the Murray at Barham and thousands of Murray cray have walked to the edges of the river from Echuca through to Swan Hill.

NSW Department of Primary Industries Fisheries and OzFish have been active across the region collecting the crays transporting them to the Narrandera Fisheries Centre. The facility is said to be able to handle 8,000 crays.

OzFish Fish Emergency Recovery Teams had been granted permission by NSW Department of Primary Industries Fisheries to commence a relocation and recovery operation from Thursday, October 27. On Sunday, October 30, they were in Barham and with the help of locals, collected a van full of crays. Many of the large females were laden with eggs.

Dr John Conallin, who has both local and international research experience in freshwater fish, said that extracting the crays was a worthwhile exercise.

“They’ve come out of the water to avoid that dissolved oxygen.

“They’re able to come in and out of the water and use that to survive – how long they can do that for, we don’t really know.

“With fat supplies in their body, how long can they maintain them, because they’re obviously not feeding at that time and the other thing is that it increases predation.

“They’re much more vulnerable to humans, and to birds and other things that will prey on them.

“What we do know is cray populations have decreased after hypoxic blackwater events, so it does have an effect. We’re seeing that in Deniliquin with cray populations and we’re also seeing that in the Murray.

“The other thing about crayfish is they’re very slow to recover. We need more work done on crayfish to work out what flows and conditions are best for them, can we breed them in numbers where we can restock them and work in with community groups as we did with other fish?

“The targeted programs around catching crays taking them to an area such as fisheries or Charles Sturt University fish lab, you store them there and then you put them back.

“In my opinion, that’s a warranted exercise because they can’t move out of the area like cod and golden perch can and we know there are impacts.”

Fish have also been found in distress along the waterways, with Murray Cod being the main feature. Dr Conallin shared his thoughts on the overrepresentation of cod.

“They (cod) certainly are affected in numbers more than golden perch and silver perch.

“There is some data around that shows that golden perch and silver perch move out of the system as quickly as they can when it comes to blackwater.

“Cod are much more localised and territorial to a region, that’s probably why they hang on until the last minute.

“Then, when they’ve got to get out, that’s when you find them right out onto the perimeters of the areas, like pushing into the forest, then that’s their downfall.”

Dr Conallin believes some of the larger cod do move out of harm’s way.

“We do get large cod back in the system, so here in Deniliquin or down at Barham in the Murray, say two years after a blackwater event, you can catch an 80cm cod. It didn’t grow that big in two years, so where did it come from?”

Many wonder what the contributing factors are that are causing or influencing the current fish kills. Does holding huge volumes of environmental water in the forest for months before a natural event play a role? How much sewage ended up in the river from the likes of Echuca and Rochester? Do the current policies promoting high forest floor debris play a role?

Fish kills can be reported to the NSW (1800 043 536) or Victorian Governments (1300 372 842).

This article appeared in The Koondrook and Barham Bridge Newspaper, 3 November 2022.