Carp are bottom feeders, stirring up mud, engulfing invertebrates in their large mouths and dislodging weeds, which float to the surface and die. This makes the fish particularly troublesome in the shallow waters of wetlands that border the river.

The Murray's flow was always episodic, and these wetlands periodically flooded and drained; a natural cycle that prompted native trees to germinate and native birds and fish to breed. The erection of locks and weirs ended that cycle, and the river is now a series of ponds. Only a fraction of its normal flow remains, its mouth has all but closed, and many of its wetlands are now dustbowls.

Some, however, are being reclaimed. River water is diverted to flood them artificially, then drained months later to simulate droughts. But carp come with the water. Some wetland access points are fitted with carp screens, which admit carp no larger than a finger. These die when the wetlands are drained and before they can grow large enough to cause problems, but excluding tiny carp means excluding most native fish as well. Other gates, built with larger mesh, admit larger carp.

Civil and Environmental Engineering students at Adelaide University have been researching a series of deterrents which they hope may selectively prevent carp from entering wetlands under rehabilitation.

"We feel that we might be able to use one of our deterrents to exclude or at least reduce carp movement into wetlands, and that one of these behavioural methods might not affect native fish so much," said Amy Ide, one of the team of Honours students.

The researchers are examining a range of options, including light, sound, bubble curtains and physical barriers. A giant flume in the department is flooded with water, and carp intro
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Contact: Dr Martin Lambert
mlambert@civeng.adelaide.edu.au
618-8303-5838
Adelaide University
4-Dec-2001