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Emerging technology could solve ‘ludicrous’ fish loss from irrigation

Irrigation - either via diversion channels, or from pumps drawing directly from rivers - kill many millions of native fish a year.

Irrigation – either via diversion channels, or from pumps drawing directly from rivers – kill many millions of native fish a year.Credit:Twitter, via Lee Baumgartner, CSU.

In fact, millions of fish die each year, either by being sucked into dam storages and crop fields, or being lost in irrigation canals. NSW alone has more than 4500 irrigation pumps.

The concern isn’t new. In May 1946, the West Wyalong Advocate decried the “thousands probably millions of little Murray cod and other fish … going to waste” in Leeton’s irrigation canals off the Murrumbidgee River.

Fifty years on, NSW Fisheries staff labelled as “hypocritical” the limit on an average angler’s take when irrigators sucked up “large numbers” of fish and spawn with water pumps extracting 100 million litres or more each day. Worse, some irrigators sold their “illegal” harvest, a document from December 1995 shows.

“We’re losing hundreds of millions of fish below the surface but no-one bats an eyelid,” Matt Hansen, president of recreational fish group Inland Waterways, said. “It’s absolutely ludicrous we can be doing it in this day and age.”

Graeme McCrabb steers his tinnie towards dead fish near Menindee after the second of three mass fish kills on the Darling River at Menindee during the 2018-19 summer.

Graeme McCrabb steers his tinnie towards dead fish near Menindee after the second of three mass fish kills on the Darling River at Menindee during the 2018-19 summer.Credit:Nick Moir

Backed by a $1 million grant from the Victorian Environmental Water Holder, the “Australian-first” trials of the self-cleaning screens examined whether they could prevent fish larvae ending up in a canal at Cohuna while keeping the reduction of water levels to less than 2 centimetres.

Farmers got water without disruption, while screens diffused plant and larval drift so most didn’t get through the 2-millimetre wide mesh nor did they clog up the mesh.

Of 160 Murray cod larvae detected on average each day drifting in the current, none were found on the other side, Ms Bullen said.

Craig Boys, a fish ecologist with NSW’s Department of Primary Industries who has helped champion the technology, said his agency was working “with a number of willing farmers”.

Fish

Fish

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“Modern screens also help farmers reduce clogging from sticks, leaves and other debris which can end up in their water supply, which saves them money on maintenance, electricity, fuel and filters,” Dr Boys said.

Brett Kelly, managing director of the Cohuna-based AWMA Water Control Solutions, admits irrigators will need some convincing, not least because the screens cost up to $1 million each.

“If you mention ‘screen’ to a farmer, they think you’re swearing at them,” Mr Kelly said.

Still, he’s confident governments will help share the funding burden, noting the millions they spend on building fish ladders, breeding and restocking native species.

“It’s really strange – all that effort going to fish,” Mr Kelly said. “Then we just suck them out by the millions.”

Gunbower Creek wetlands, near the Cohuna irrigation canal that is being screened to prevent native fish loss.

Gunbower Creek wetlands, near the Cohuna irrigation canal that is being screened to prevent native fish loss.Credit:Nick Moir

Michael Murray, general manager of Cotton Australia, said: “As an industry we recognise the importance of native fish as one of the key indicators of a healthy river system and we are open to considering all ways to ensure healthy fish populations.”

“Fish screens are a relatively new concept in Australia, so it is really important to get this local research, before jumping to any conclusions, or wholesale endorsement of fish screens,” he said.

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Lee Baumgartner, a fish ecologist at Charles Sturt University, said similar technology was already used in Europe, the US and mandated in parts of New Zealand.

Savings to farmers in terms of maintenance avoided in unclogging their own pumps of vegetation, fish and even platypuses would deliver a “win-win” for all.

“Every time we put one on a pump, you’re saving thousands of fish,” Professor Baumgartner said.

“The river needs that right now.”

One of the four fish screens is lowered into a canal at Cohuna in northern Victoria.

One of the four fish screens is lowered into a canal at Cohuna in northern Victoria.Credit:AWMA, North Central CMA

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