Faster flows trigger fish breeding frenzy

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Frisky fish have taken advantage of a river pulse to spawn in the waters of the Murray River. A small, fast flowing event took place in October, designed by the NSW Department of Primary Industries (Fisheries) and Victoria’s Arthur Rylah Institute, to support native fish breeding.

And it appears to have been a success.

Monitoring has detected promising numbers of native fish larvae.

Both sides of the border are likely to see the benefits as the next generation of native fish grow and migrate.

NSW DPI Senior Fisheries Manager Dr Katherine Cheshire said environmental water was used to create suitable breeding conditions.

“All fish need water to survive, but in order to support breeding, conditions need to be just right,” Dr Cheshire said.

“Fish, like golden perch and silver perch, are thought to be ‘flow-dependent specialists’.

“They require water to be flowing quickly at the right time of year in order to breed successfully.

“Their biological rhythms are linked to changes in water speed, temperature, depth and turbulence.

When the conditions are right they start to breed and the intensity of that breeding increases with higher flows, particularly those that inundate the flood plain.

“After spawning, perch eggs and larvae drift downstream for days and/or weeks before settling into juvenile habitat.

“If river flows are high enough and water is flowing over the river bank or out into the creeks, the juveniles move with it into the nutrient-rich waters of the floodplain.

“There, they grow to be fat, happy fish before returning to the river when waters recede,” she said.

Dr Cheshire said golden perch and silver perch may spawn without floods or flow pulses but spawning intensity may be reduced.

“The results of this project will help to inform the management of environmental water on both sides of the border,” Dr Cheshire said.

“By understanding the complex requirements of native fish, water managers can target those needs and deliver water most effectively,” she said.

Researchers from Victoria’s Arthur Rylah Institute are keeping a close eye on the event as part of The Living Murray and Murray Darling Basin Authority monitoring program.

Senior scientist Zeb Tonkin said drift net surveys were being conducted during the peak perch spawning period.

“Monitoring so far has detected both golden and silver perch spawning as a result of the pulsed delivery of environmental water,” Mr Tonkin said.

“In spite of a relatively dry season, we are still seeing some great outcomes for fish.

“We hope to track the outcomes of this spawning using annual surveys targeting juvenile and adult fish in the Barmah-Millewa region and beyond.

These species are known to move beyond the Barmah-Millewa region of the Murray River as they grow up.

“Using findings from surveys conducted at other sites along the Murray and its tributaries can help track the success of these spawning events,” he said.

The Victorian Environmental Water Holder worked with the Goulburn Broken Catchment Management Authority to manage the delivery of water supplied by TLM and the Commonwealth Environmental Water Holder.

Commonwealth Environmental Water Holder David Papps said the project was testament to the collaborative efforts of scientists, environmental water managers and environmental water holders.

“Creating opportunities for native fish movement and breeding is not only good for the environment, it is also good news for the Murray Darling Basin’s 430,000 recreational anglers,” Mr Papps said.

“Recent successes reaffirm that using the right volume of environmental water in the right location at the right time and at the right temperature has real benefits for native fish.

“Using water carried over from 2014/15 to provide variable flows has improved connectivity between the river and a range of floodplain habitats and food sources around the Barmah-Millewa Forest,” he said.

The watering project has been a collaboration between the NSW Office of Environment and Heritage, Victorian and Commonwealth authorities, NSW Department of Primary Industries (Fisheries) and Victoria’s Arthur Rylah Institute with water from The Living Murray and Commonwealth Environmental Water Holder managed by the Victorian Environmental Water Holder, MDBA River Operations and Goulburn Broken Catchment Management Authority.

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