Environment

‘Extremely vulnerable’: Agencies fear bigger fish kills this summer

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Authorities are preparing emergency response teams as scientists warn that fish kills are looming in the states waterways on a scale that could dwarf the mass die-offs last summer.

Governments "hold grave concerns for communities and rivers across the northern basin which remain under considerable stress because of the drought," a Murray-Darling Basin Authority spokeswoman said.

Carcasses after the second of three mass fish kill events in the Darling River at Menindee in January 2019.

Carcasses after the second of three mass fish kill events in the Darling River at Menindee in January 2019.Credit:Nick Moir

"Fish remain extremely vulnerable in the north and will remain so until significant inflows are received."

NSW agencies including WaterNSW and the fisheries unit of the Department of Primary Industries are "preparing early for the carnage", said one official, who requested anonymity. "It's going to be messy."

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Lee Baumgartner, a freshwater fish ecologist at Charles Sturt University who took part in one of several inquiries into last summer's mass fish kills at Menindee in western NSW, said researchers treated those events "as not yet over".

"The biggest problem weve got right now is that the majority of the Darling is still dry and not flowing," Professor Baumgartner said.

“If theres no significant rainfall between now and when it starts to get really hot out west, we can expect it to be a pretty nasty season in terms of water quality and fish deaths.”

Without flows, the water is susceptible to blue-green algal outbreaks that can be toxic to humans and wildlife.

The algae also help suck oxygen out of the river, particularly if there a sudden cool snap that kills some of them off – which was a key trigger to last summer's die-offs.

Graeme McCrabb on his tinnie in the Darling River, floating among dead Murray cod and other fish just after the second of three big fish kill events near Menindee.

Graeme McCrabb on his tinnie in the Darling River, floating among dead Murray cod and other fish just after the second of three big fish kill events near Menindee.Credit:Nick Moir

The key tool for flushing out the algae would be environmental water releases but average storage levels in the northern basin are 9 per cent and falling.

Menindee Lakes are 1 per cent full, while Keepit Dam and Split Rock dam are just 1 and 2 per cent full respectively, leaving the Namoi River they supply particularly at risk.

“Youve no ability to provide flows down the Namoi,” Professor Baumgartner said, adding the Murrumbidgee, site of smaller fish kill events last summer, could also be at risk of algal outbreaks.

While government staff worry about "a disastrous" summer, the Berejiklian government is downplaying the threat for now.

“Fish kills are always a risk with persistent drought conditions across the state," a spokesman for Adam Marshall, the Agriculture Minister, said. "The NSW government is working on ways to reduce the impact of fish kills.”

Similarly, the Department of Primary Industries said it was "aware of the risks and will provide further information on this and our response strategy in the near future".

The outline of the plans, though, is becoming clearer, such as preparations for salvage operations to relocate critical breeding stock of Murray cod, silver perch, and other threatened species to nurseries at Narrandera.

The authority, meanwhile, has conducted a review of the efficacy of different types of aerators – devices used to mix oxygen into hypoxic water. It found some performed better than others, a finding that could be handy if the NSW government lRead More – Source