Colourful carp pose threat to our waterways

KOI carp may be beautiful but they pose a serious threat to the Manning’s waterways.

That’s the worrying message heard by Greater Taree Council’s Lower Manning Wetland Advisory Group at a recent meeting.

Dr John Harris, a river ecologist and fisheries scientist who lives at Bootawa, told the group common carp have invaded waterways around the country and are still spreading, seriously degrading the ecology of rivers and wetlands.

He said in large areas of the Murray-Darling basin, carp constitute up to 80 to 90 per cent of the total biomass of all fish. A study in the Bogan River had found an average of one carp for every square metre of the water surface area. Following inland flooding in 2010-2011, billions of young carp have been bred.

This alien pest fish is also damaging many coastal rivers, notably the Hawkesbury, Hunter and Shoalhaven.

Dr Harris said carp interfere with waterway ecology in two main ways: they feed among waterway sediments, making the water turbid and uprooting aquatic plants; and their enormous numbers can overwhelm native fish and other aquatic animals as well as degrading water quality.

Warm, shallow wetlands such as those in the Cattai and other lower Manning wetlands are particularly vulnerable. He predicted that if carp became abundant in the Manning there would be a sharp increase the cost of treating the region’s municipal water supply.

Studies have shown after being released into waterways, the koi’s distinctive bright colouring fades and most come to resemble other wild strains of common carp.

Most people know not to deliberately release fish into waterways, however a strong risk still exists from koi kept in ponds or dams that can overflow in times of heavy rain or flood.

Cr David West from the wetland advisory group urges residents to report sightings of aquatic pests in the local catchment to the Department of Primary Industries hotline 02 4916 3877 or by email aquatic.pests@industry.nsw. NSW DPI list all carp strains as a Class 3 noxious species, and the listing is currently being revised to bring it into line with more-stringent national guidelines.

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