Operation necessary to stop fish dying after flows are cut off to maintain water supplies to stock and domestic users

This article is more than 1 year old

This article is more than 1 year old

New South Wales fisheries workers are attempting to rescue distressed Murray cod near Menindee in the state’s west by catching them in nets and trucking them to a fish hatchery hundreds of kilometres away.

The NSW primary industries department (DPI) confirmed the operation was under way on Thursday morning and was necessary because authorities would be cutting off water flows from Menindee’s weir 32 “in the near future to maintain town water supply”.

As part of drought management, WaterNSW has indicated it will cut off flows from weir 32 to maintain water supply to stock and domestic users and high security water licence holders around Lake Wetherill and the weir pool.

Cutting off the water flows would make already distressed fish at the site of the state’s mass fish kills more susceptible to danger from low levels of dissolved oxygen in the water, the department said.

The fish are in the pool immediately downstream of weir 32 and if they can be safely removed will either be trucked in a fish-stocking truck to the Narrandera Fisheries Centre – 590km from Menindee – to be used in breeding programs or they will be released in the lower Darling near Wentworth, 240km away.

Cameron Lay, the NSW DPI’s Murray Darling program leader, said fisheries officers were mid-operation by noon on Thursday and initially focused on a group of 20 to 30 large Murray cod that had accumulated in a single area on the surface of the water.

“They’re exhibiting very unusual behaviour, they’re at the surface of the water and side by side,” he said.

“They’re trying to take advantage of a very small source of oxygenated water that’s coming through weir 32.”

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Lay said the first goal of the operation was to maintain the genetic and cultural connectivity of those particular fish with that part of the river by taking them to the hatchery for use in breeding programs.

“This will allow us to restock the river when conditions improve with direct descendants from the river,” he said.

“And eventually we’ll return those actual fish back to the Darling river once they’ve finished their role with our breeding program.”

Early assessments suggested the 20 to 30 fish were all well enough to be suitable for the breeding program, he said.

Once the first group is transported, fisheries officers will decide if more fish from that location need to be moved to the hatchery or downstream.

Because of the decision to cut flows from weir 32, there is a risk that more fish kills might follow.

Facebook Twitter Pinterest The relocated Murray cod are being taken to a hatchery to be used for breeding to replace the thousands of fish that have died. Photograph: Graeme Mccrabb Handout/EPA

“It’s certainly possible, however WaterNSW have very few options available because the weir pool is part of critical town water supply,” Lay said.

Under WaterNSW definitions, stock and domestic use refers to normal household purposes around the house and garden and drinking water for stock.

High security use can apply to town water supply, or to irrigation of permanently established crops, such as orchards.

The DPI said relocating the fish was not their preferred solution because of the additional pressure it places on already stressed fish.

But it had assessed that the risk of leaving them at their current location was greater because the decision to cut flows from weir 32 would leave the fish more susceptible to threats from low levels of dissolved oxygen.

Lay acknowledged that there was a possibility that some of the fish might not survive the rescue attempt.

“There’s certainly a risk. We’ve been well aware of that from the beginning of this operation but we consider the risk of leaving them in the river was far greater,” he said.

Richard Kingsford, the director of the Centre for Ecosystem Science at the University of NSW, said the plan was a sign of “desperate times and desperate measures”.

“I think there’s some reasonable argument for doing this but we need to know what happens,” he said.

He said trucking the fish hundreds of kilometres between Menindee, Wentworth and Narrandera could also be risky.

“My uncertainty is if these fish are already stressed, the question is what would the operation do in terms of causing further stress?” Kingsford said.

“And the bigger issue is if we’ve got a river without much water in it, how often are we going to have to do this, how often are we going to have to intervene to save fish in this river?”

Late on Thursday the department said fisheries officers had removed 20 fish from the river and they were on the road to the hatchery at Narrandera.

“The fish are being taken to Narrandera Fisheries Centre, as it is expected the water quality and monitoring systems there will give them the best chance of recovery,” a spokesperson said.

“It is expected that the 20 Murray Cod will have a productive potential of more than 100,000 fingerlings per year.”