Pest or Guest: The Zoology of Overabundance
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Common carp are one of Australia's most despised introduced freshwater fish and have been implicated in the degradation of inland river systems. Although present in Australia for ~150 years, carp did not become a recognised pest until the appearance of the Boolarra strain in the 1960s. Following colonisation of the Murray River, and aided by widespread flooding in 1974, carp populations rapidly spread throughout the Murray-Darling Basin and established populations in all states except the Northern Territory. Although commercial, anecdotal and some scientific data suggest that carp populations have since declined in many areas, the species continues to spread and invade new waterways. Numerous forums and workshops have been held to develop and progress with potential carp control solutions. However most assessments of potential control alternatives have failed to provide effective means of managing the problem. These have included assessments of over-harvest, trapping, poisoning, exclusion, bio-controls, biotechnologies and habitat manipulation. However within the last few years, at least four initiatives are beginning to show some promise. These include: the Tasmanian Carp Management Program which utilised physical removal activities directed by a ‘Judas fish’ program, carp drafting devices named ‘William's Carp Separation Cages’ designed to remove carp as they migrate through fishways, a novel molecular genetic approach, ‘Daughterless Carp Gene Technology’ designed to integrate an inheritable gene into the population that limits the abundance of the highly fecund females, and the identification of discrete and finite carp breeding hot-spots within river systems, in order to provide targeted control options.