The introduction, spread and ecology of redclaw crayfish Cherax quadricarinatus in the Zambezi catchment
Two of the four crayfish species brought to Zambia for aquaculture since 1979 are now naturalised. Procamburus clarkii occurs in the Maramba River at Livingstone, close to a former fish farm, whereas Cherax quadricarinatus, deliberately introduced to a number of sites in the Zambezi and Kafue River catchments since 2001, is now widespread and highly invasive. High rates of dispersal, up to 111 km y−1 downstream, might be the result of passive transport on floating vegetation. Significantly more synodontid Synodontis sp. catfish were caught in Fladen traps in the Kafue River in crayfish-free areas compared with crayfish-infested areas, but the possibility that synodontids became trap averse in the presence of crayfish was not ruled out. No difference was found in the numbers of Single-spined River Crab Potamonautes unispinus caught in crayfish-free and infested areas. Alien temnocephalans, commonly found on crayfish, are now also present on crabs P. unispinus on the Kafue Flats. The artisanal gill net fishery has been harmed by the introduction of C. quadricarinatus and no significant commercial fishery has developed. However, without more information on the adverse impacts, and stronger fisheries regulation, there is a high risk C. quadricarinatus and P. clarkii will be introduced to uninfested catchments with irreversible consequences for artisanal fishermen and the environment.
Keywords: invasive species, Kafue River, Potamonautes unispinus, Procamburus clarkii, Synodontis