Fresh flow may be lethal to fish
Friday, 11th March, 2016
By Michael Murphy
The state fisheries authority is calling on the public to report fish kills as a small flow makes its way down the depleted Darling River.
A very small amount of water - about five to ten gigalitres - could arrive at Menindee later this month and be captured in the river channel at Lake Wetherell.
But DPI Fisheries says the flow may decrease in magnitude as it moves through the system, posing a risk to fish in the downstream sections above the Menindee Lakes.
While the benefits of a flow are obvious, in some cases they can be lethal to native fish stocks eking out an existence in extreme conditions.
The summer flow has replenished town weir pools along the river, but it would not have a “material impact” on water levels.
“River flows will hopefully re-instate connectivity between isolated pools,” a department spokesperson said.
“Moderate flows would be expected to provide some relief to native fish currently taking refuge in these remaining pools.”
The river at Bourke was now falling with a peak downstream at Louth. The river at Tilpa was flowing at 750Ml per day and rising.
There was no flow yet beyond Wilcannia.
“It should be noted that there is no significant flow behind this event therefore without more rainfall and inflow the river will naturally recede again in coming few months,” the spokesperson said.
Flows at this time of year may provide opportunities for spawning for smaller species, but not Golden perch (Yellow belly) and Murray cod.
“Bigger fish will benefit from the additional habitat and food which accompanies larger flows.”
DPI Fisheries has warned of the risks of small flows during the hot weather, saying that de-oxygenation of water can be lethal.
“Bigger fish like Murray cod require more oxygen to support their greater body size, and therefore are often most affected,” the spokesperson said.
“Without additional inflows to the catchment, there is little that can be done to mitigate oxygen depletion.
“Allowing the most of the inflows to progress downstream naturally may reduce the potential for this to occur.”
The department urged the public to report any instances of “distressed or dead fish” via the Fishers Watch hotline on 1800 043 536.