Invasion by zander and the management of fish stocks

Abstract

In 1976 it became evident that the zander ( Stizostedion lucioperca (L.)) had been illegally introduced into waters coming under the jurisdiction of the Severn-Trent Water Authority. Since that time the species has established self-sustaining populations in a 35 ha lake and a 40 km length of canal system, with the start of a similar trend being observed for the River (Lower) Avon. The mechanism of invasion in terms of distribution and population growth suggests that, although the species can rapidly become established in a suitable habitat, further colonization of new reaches of a watercourse (if unaided by man) can be slow. The impact on recipient fisheries depends on the rate of expansion of the zander population and the ability of resident prey communities to withstand an additional predator. In an enclosed lake, management of fish stocks has proved possible. For open-ended watercourses, the monitoring and control of zander populations is difficult, but continual cropping by anglers is recommended, to maintain a diversity of species.