Aquatic ecologist Dr Keith Bishop has recorded some “extraordinary observations” during his river-long fish survey of the Manning River, which started this May.
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Dr Bishop takes a ‘do no harm’ approach to his studies.
“My work is all based on direct observation work. Normal surveying is to go out there and put out nets and electrocute and poison - I don’t like that kind of work,” he said.
“So I’ve tried to develop direct observation work so you don’t damage what you’re looking at. And also you can come back again soon and you haven’t interfered with what you’re looking at as well.”
After the moderate flooding in March due to the after effects of Cyclone Debbie, native fish have been gorging themselves on El nino-weed-loving goldfish in the Manning River.
The goldfish in question are a species of East Asian carp. Dr Bishop says the species appears to have been introduced from the Gloucester River possibly 10-20 years ago.
Large numbers of larger native fish such as the Australian bass, long-finned eels and bullrouts were ambushing the goldfish and consuming them.
- Dr Keith Bishop
The commencement of an El Niño pattern in 2013-14 caused low river flow in our river system, resulting in a lack of floods to clean the river and catchments of weed.
Consequently the native plants in the river grew profusely, to such a state that it caused a major fish kill in the Nowendoc River last summer.
The overgrowth of weed created ideal conditions for the goldfish to thrive in, as they use the plants to attach their eggs to and provide shelter and food for their juveniles.
The high river flows in March saw greater than 95 per cent of the native plants being ripped out, making the goldfish visible.
“They had no option but to occupy open areas,” Dr Bishop said.
While surveying the river at night last week, Dr Bishop saw thousands of goldfish (which are not gold, but grey in colour when in the wild), resting on open gravel beds with no plant protection.
“Large numbers of larger native fish such as the Australian bass, long-finned eels and bullrouts were ambushing the goldfish and consuming them,” Dr Bishop said.
“In places fine silt and debris was being sent up into the water column as wild attacks occurred – as we approached from downstream we knew there was ‘action’ going on a short distance upstream.”
This is good news, Dr Bishop explained, as the goldfish are bad for rivers as they stir up river beds which release nutrients that cause algal blooms.
Julia Driscoll
Julia Driscoll has worked as a journalist for the Wingham Chronicle and Manning River Times since 2014. She values the deep connection with community that being a rural and regional journalist brings.
Julia Driscoll has worked as a journalist for the Wingham Chronicle and Manning River Times since 2014. She values the deep connection with community that being a rural and regional journalist brings.
