Water Kills Cod

Hundreds of fish, including giant Murray cod, have died following the release of domestic and stock water in the Wakool system in southern New South Wales. The deaths of the cod, some more than 50 years old, along with golden and silver perch and European carp, is an unnecessary tragedy.

The fish died in two incidents involving water flows into Collegin and Merran Creeks. Exacerbating the event is the revelation that this isn’t the first time such devastation has happened.

Tim Betts’ farm is 20-kilometres north of Swan Hill in southern New South Wales. He hasn’t had water for four years but loves his land, which includes a 5-kilometre frontage of Merran Creek – a highly regarded Murray cod habitat.

Prolonged drought caused the creek to dry up into a series of holes a kilometre or so apart. These holes, separated by the dry sand creek bed, offer refuge to big fish like cod. It’s a natural event. Native fish have evolved to withstand drought, and the deep water holes that fill with smaller fish and crustaceans like shrimp, offer a smorgasbord of sustenance while the cod wait for the water to flow again.

An unnatural, man-made event appears to have spelt disaster for these fish. On that day, with the mercury hovering about 46 degrees Celsius, the New South Wales Water and Energy Department released about 80 ML of water for stock and domestic needs. It was a minimal, albeit fatal flow. As the water passed over the sand it heated up. By the time it arrived at the holes it was acidic and deoxygenated – a lethal mix for the fish.

Three days after the water was released, Mr Betts noticed dead fish floating to the surface, hundreds of them including old Murray cod more than a metre long and weighing better than 25 kg. Murray cod are one of the largest freshwater fish in the world and can grow to 1.8 metres in length and 113.5kg in weight. Research has shown a Murray cod take at least 15 years to reach a metre in length, and their life span is estimated to be 75-114 years.

“I’ve had no water for four years and I’ve put up with it but the water policy as it is being enacted is just killing the life in our rivers,” Mr Betts said.

“I consider this to be a major ecological disaster; fisheries officers inform me that it will take a minimum of 10 years for the aquatic population in the creek to recover, if ever.

“This water flow has come far too late and been far too meagre, to achieve the desired outcome. To release a flow of water when the forecast temperature is to exceed 40 degrees for a fortnight is ludicrous.

To run water over red-hot sand into existing refuge holes is going to automatically kill fish, let alone knowing that the volume of the flow would not be enough to oxygenate the water is a recipe for disaster.

On the day the water was released it was 46 degrees and I reckon the exposed sand on the riverbed was 60 degrees or hotter.

“It takes about three days for the fish to float after they die and I counted 30 dead cod to about 25 kg before I stopped, and the birds were feeding on hundreds of smaller fish.  Even the shrimp in the creek are dead – the water will take years to recover with big cod, and this probably won’t happen in my life time.”

The Murray Cod has been listed as a vulnerable species under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). The species is not listed as threatened in NSW, but is identified as a member of the listed endangered ecological community Aquatic Ecological Community in the Natural Drainage System of the Lower Murray River Catchment (Fisheries Management Act 1994).

Rob Loats, president of Mid Northern and Wimmera Anglers Association, described the flow-related fish kill as “extremely disappointing, again,” saying there had been a hard won resurgence in Murray cod over the past 10 years. “We didn’t need this; the fish and general aquatic environment are having a difficult enough time as it is,” he said.

The NSW Department of Water and Energy acknowledged the fish kills occurred after it released water into Colligen and Merran Creeks in the Wakool River system, west of Deniliquin.

Department spokeswoman Bunty Driver said there were three replenishments and the first the department heard of a problem was when the dead fish were reported in the Merran Creek during the second replenishment.

“It is difficult balancing the needs of the environment and people in need of water, “ she said. “There have been reports of other fish deaths in the Murray Valley due to high (33-37 degrees) water temperatures in shallow areas.”

In a statement, David Harriss, deputy director-general of the department said: “Fish kills in both creeks are the result of the oxygen level at the head of the flow being reduced to a very low level by a series of unexpected hot days above 40 degrees, the collection of organic matter and potential liberation of sulphidic sediments.”

Mr Harriss said there were also reports of fish dying in other parts of the Murray Valley not associated with any release of water, but primarily due to the extreme heat.

He described it as an “unfortunate event” and said department was working closely with NSW Fisheries, CSIRO, State Water and local landholders to modify the water delivery plan to improve water quality in the creeks.

Two weeks after Mr Harriss issued his statement another fish kill occurred, this time in the Neimur River due to water being released from Collegin Creek. John Manual came across hundreds of native fish including more than 30 big dead cod, 10 of them more than 15kg, including a 1.2 metre long cod.

Like Mr Betts, Mr Manual was angry at what he believed was environmental mismanagement. “It’s bad enough that this cod kill happened, but we had a cod kill last year in the Wakool River for the same reason,” he said. “I understand farmers need water, but we need better water management because no-one wants a river where there is no life.”

Mr Betts said: “Anglers spend hundreds of thousands of dollars helping to pay to restock these waters and rebuild Murray cod stocks and then something like this happens.

“What’s the good of a three month closed season and a 60 cm size limit on Murray cod when this action is allowed that kills hundreds of cod?”

It all seems like an ongoing case of déjà vu, where water management authorities are failing to heed past lessons.

In January 2004, the Darling River between Menindee Lakes and Pooncarie turned it into an environmental killing field. Fifty per cent of the Darling River bed was dry and cod and native fish had taken refuge in deeper holes. The Department of Infrastructure, Planning and Natural Resources released 150 ML of water from Menindee, followed by a second 150 ML release, water described by locals as green with slime on top.

Subsequently the riverbanks and snags in the river were littered with the decaying corpses of big Murray cod. In that case pollution and lack of oxygen in the water were blamed and farmers along the river said they had not seen or heard of a cod kill of that magnitude.

Cattle producer Bill Arnold said at the time that water passing over hot ground in the riverbed before entering the more permanent pools would have been like water running through a hot water service.
“Our water hole is 15 feet deep and the water temperature at the top is 30 degrees Celsius, and 15 feet down, it’s still 30 degrees, so the cod had nowhere to go.”

A spokesman for the then NSW Department of Infrastructure, Planning and Natural Resources, since renamed NSW Water and Energy, blamed high water temperatures and lack of oxygen. Such familiarity sounds fishy.


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