Invasive carp - trapped by their own behaviour

A weir keeper,Alan Williams, has invented a trap which could help to capture a large proportion of the carp which have invaded the Murray-Darling River Basin in New South Wales, Australia.

Native fish species do not jump, but carp do.

Alan's ingenious trap, developed in collaboration with Ivor Stuart from Victoria's Department of Sustainability and Environment, takes advantage of this difference in behaviour.

On entering the trap, carp jump into a second cage and trap themselves - ready for later collection. By contrast, native fish swim straight through the trap, without jumping, and leave unharmed.

In trials, this trap has removed up to 90% of the carp in a stretch of river!

Carp were deliberately introduced to Australia in the 1850s, and have also become serious pests in New Zealand, North America and Europe.

As bottom feeders, carp eat aquatic plants and stir up sediments. The muddy water they produce not only has lower light penetration, less plant growth and reduced oxygen concentrations, but is also less suitable for most native fish.

Prior to this invention carp were very difficult to catch. Fortunately, Alan and Ivor have decided not to patent their invention and to make the trap as widely available as possible.

In 2004, Alan and Ivor won a well-deserved A$10,000 Eureka prize from the Australian Museum.