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Author Topic: Fish dying in Murray River but huge number of cod larvae spawn in lower Darling  (Read 3128 times)

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Fish dying in Murray River but huge number of cod larvae spawn in lower Darling
by Emma Brown - ABC Rural

Murray cod are spawning in huge numbers in the lower Darling River.

Ecologists and landholders are thrilled that the major river, which only four months ago was dry below the Menindee Lakes, is now teeming with Murray cod fingerlings.

Fisheries project officer Iain Ellis, from the New South Wales Department of Primary Industries (DPI), said the spawning event was great news as native fish populations had not been strong.

"There has been a massive spawning event by the cod that remain in that part of the river," he said.

    "Our monitoring team out there has detected larger numbers of cod larvae than pretty much ever detected in the Basin before, so that's been a great response.

"Right now, what we are hoping to see is further increases in flows, even just marginal increases, that will start to fill a bit more of the river channel [and] inundate a few more snags, sand banks and benches which all produces nutrients and therefore food for these guys."

Higher river flows needed to keep larvae alive

Mr Ellis said the huge spawning event could be attributed to the cod's instinct to rapidly reproduce in times of flood, having evolved to suit the Murray-Darling Basin's cycles of boom and bust.

He said the fish larvae would find it challenging to survive if no additional releases were sent down the river from the Menindee Lakes as they would rapidly run out of food.

"It's pretty clear, as a fish ecologist, that with the flows coming through past Menindee Lakes from the northern Darling catchment, those flows are carrying important flood cues, so there's lots of nutrients in the water," he said.

"As a result, the adult fish in the lower Darling below Menindee have responded and invested heavily in eggs and in spawning this year.

    "Those fish are assuming, as they are evolved to do, that there's more water on the way and the river will continue to rise.

"When you do get higher flows or some floodwaters, you do get stronger recruitment or survival or the larvae in to adulthood."

Blackwater leading to fish kills in Murray River

Large floodwaters are moving through the Murray River and have picked up tannins and carbon matter along the way leading to a blackwater event.

With the oxygen levels in the Murray dropping around Mildura and Wentworth and other blackwater events occurring in the Edward and Wakool Rivers, it is expected there will be fish kills.

Mr Ellis said an additional flow in the Darling would assist some distressed fish to escape the blackwater.

But he said he understood the concerns of communities along the lower Darling River who did not want to see the Menindee Lakes drained and risk another extended period of dry river.

"Although we won't dilute the blackwater in the Murray system, having some fresher water coming down from the Darling would provide a bit of a cue for the fish in the Murray that are really struggling for air to move up in the lower Darling where there's a bit of a refuge for them.

"So it would enable some fish to survive that might otherwise die.

"If we do get a big pulse from Menindee we'll probably also see Golden Perch respond and spawn.

"It would be a win-win-win and it's not going to have any affect on water security at the Menindee Lakes."


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