Can management of freshwater fish populations be used to protect and enhance the conservation status of a rare, fish-eating bird, the bittern, Botaurus stellaris, in the UK?

摘要

The bittern, Botaurus stellaris (L.), is a Red Data list species in the UK with currently approximately 30 breeding males restricted to a few wet reedbeds, the majority of which are located in the East Anglian region of England. Although having a diverse diet, the bittern is mainly piscivorous, and eels, Anguilla anguilla (L.), and rudd, Scardinius erythrophthalmus (L.), are their main prey species. The EU Species Action Plan for the bittern targeted degradation of wet reedbed habitat and food availability as the two main threats and limiting factors to the conservation status of bitterns. To date, most conservation work has focused on the rehabilitation and creation of wetland reedbed habitat with little or no manipulation of the available or required food base, because of a paucity of knowledge regarding the habitat requirements of fish species in wetlands. Research was undertaken at a key bittern-breeding site in the UK to assess the impact of habitat management on the dynamics of resident fish populations and their availability to bitterns. Fish stock assessments indicated that current management techniques, in particular reedbed lowering, open water creation and the extensive use of sluices in complex hydrological systems, have impacted on the distribution and recruitment dynamics of fish populations within the reedbed complex, consequently affecting the potential food base for bitterns. It was concluded that fish population management must complement reedbed management regimes if current conservation targets for bitterns are to be met.