Has Australia lost another species to climate change?

The Guardian, 15 February 2020:

Drought, bushfires and rainstorms turn Australian rivers black

Luke Pearce had arrived at Mannus Creek for a three-day mission to rescue the Murray-Darling Basin’s last population of Macquarie perch.

For 10 years Pearce had visited this spot on the edge of the Snowy Mountains that, just weeks earlier, was ravaged by fire. There had been rain and the creek was flowing fast.

But as Pearce and his colleagues stood on the bank – nets at the ready – the water turned “to a river of black porridge”.

“We got there at about midday with two teams. But we were too late,” he says.

Pearce is a fisheries manager in the New South Wales Department of Primary Industries. A week earlier, he had caught nine of the endangered perch and taken them to the tanks at Narrandera Fisheries Centre.

But Pearce says nine was not enough to be confident they could breed enough in captivity to replenish the river. About 100 specimens would be be ideal, but Pearce says the fish are in such low numbers that he was hoping for 20. Hence the rescue mission on 20 January.

“It was a front of black water coming down,” Pearce says. “The water was pretty bad to start with, but it went from green to inky black.

“It was a moment of complete despair and, really, a feeling of a missed opportunity. Maybe if we’d got there four or five hours earlier we may have been able to get one or two more.”

An electronic probe in the water monitoring the oxygen levels dropped to show zero within hours, Pearce says.

“Watching those oxygen levels drop like that I had grave fears we could have lost all the fish in that system. It was devastating having worked there for such a long time to then potentially lose all this.”

The river was too black to see any fish, but crayfish, shrimp and mayfly larvae were crawling out.

What happened at Mannus Creek is one example of what scientists have described as a “triple whammy” hitting rivers on Australia’s east coast and inland.

Drought and a long-term drying has delivered a cascade of mass fish kills since late 2018, with low river flows, low oxygen and algal blooms. Authorities and politicians warned repeatedly in 2019 that ongoing drying would see more mass fish kills.

Then Australia’s bushfire crisis struck across catchments. Now heavy rain has washed sludge and ash into rivers, robbing the remaining fish of oxygen.

Hundreds of thousands of fish have died in multiple events – some caused by lack of water, and some caused by downpours running over burned catchments.

At one time, Macquarie perch was one of the most abundant native fish in the Murray-Darling system – prized by anglers and also commercial fishers.

But a NSW government assessment of the fish in 2008 wrote the building of dams and weirs had compromised spawning areas and blocked the fish’s movement. Overfishing, pollution and predation by introduced species like redfin perch had also caused numbers to plummet.

When Luke Pearce returned to Mannus Creek after the fires he was confronted with a scene of carnage. Photograph: Luke Pearce

Read the full article here.