Changes in the abundance of planktivorous fish in Lake Skanderborg during the past two centuries—a palaeoecological approach

Abstract

Fish have a profound effect on food-web structure and water quality in lakes. Quantitative historical data for fish are however scarce, which render it difficult to interpret palaeoecological records in the sediment. To reconstruct the historical changes of the fish community structure and abundance of Lake Skanderborg during the past 150 yr we conducted a stratigraphic analysis of selected zooplankton remains in the lake sediment. From these data we inferred the abundance of planktivorous (expressed as catch net −l night −l in multi mesh-sized gillnets, CPUE) and percentage piscivores using a previously developed transfer functions for Danish lakes. Inferred CPUE was high throughout the study period, being highest before 1900 after which it declined following introduction of pikeperch ( Stizostedion lucioperca) in 1903–1904. Further reductions occurred after a major reduction in external P-loading in 1974 and fish removal in 1983–1985. The inferred CPUE in the surface sediment is in accordance with recent monitoring data. Good correspondence was also obtained between measured zooplankton:phytoplankton biomass ratio and Daphnia mean body weight versus that calculated from inferred CPUE using equations established earlier from contemporary data on Danish lakes. At present, the fish stock is numerically dominated by roach ( Rutilus rutilus) bream ( Abramis brama) and small perch ( Perca fluviatilis), while pikeperch ( Stizostedion lucioperca) is the most important piscivore. In accordance with the inferred data, earlier fish investigations and angler descriptions dated as far back as to 1927 indicate little changes in fish community structure. The early dominance of plankti-benthivorous fish most likely reflects an early eutrophication of the lake due to early urban development in the lake catchment. The development of a transfer function for planktivores fish have improved the possibilities of discovering changes in trophic structure and ecological state of lakes in the past.