Managing a migratory pest species: A selective trap for common carp

Trapped common carp Cyprinus carpio display a pronounced escape behavior of jumping out of the water; this behavior is not exhibited by most Australian native fishes. Hence, there appears to be an important opportunity to exploit the unique jumping behavior of nonnative common carp to aid selective removal. We report on the Williams cage, a simple device that automatically separates jumping common carp from nonjumping fish. Between November 2002 and April 2005, the Williams cage was tested at Torrumbarry Weir fishway on the Murray River, Victoria, Australia, and trapped fish were counted every 24 h. The Williams cage successfully separated 88% of adult common carp into a confinement area. In contrast, more than 99.9% of 8,031 native fish passed through the Williams cage and exited the fishway. The Williams cage may provide a method for controlling dispersal and abundance of common carp and may be applicable to other nuisance fish species.