Changes in the fish community and water quality during seven years of stocking piscivorous fish in a shallow lake

Abstract

SUMMARY 1. Piscivores (annual stocking of 1000 individuals ha−1 of 0+ pike and a single stocking of 30 kg ha−1 of large 20–30 cm perch) were stocked in seven consecutive years in a shallow eutrophic lake in Denmark. The stocking programme aimed at changing food‐web structure by reducing zooplanktivorous and benthivorous fish, with resultant effects on lower trophic levels and ultimately water quality. 2. The fish community and water quality parameters (Secchi depth, concentrations of total phosphorus, chlorophyll a and suspended solids) were monitored between 1996 and 2000 and relationships were evaluated between predatory fish and potential prey and between zooplanktivorous or benthivorous fish and water quality parameters. In addition, potential consumption of piscivorous fishes was calculated. 3. The density of fish feeding on larger zooplankton or benthos (roach >15 cm, crucian carp >15 cm) declined distinctly during the study period. This effect was attributed to predation by large (>50 cm) pike. Based on scale readings, we cautiously suggest that the stocking of 0+ pike boosted the adult pike population to produce an unexpected impact in later years. Conversely, no direct impact of stocked 0+ pike was detected on 0+ roach. 4. A major decline in the recruitment strength of 0+ roach was observed in 2000. A combination of (i) the indirect effect of large pike preying on adult roach, with negative effect on roach reproduction and (ii) the direct predation effect of 0+ pike and/or 1+ and 2+ perch recruited in the lake, provides the most likely explanation of this phenomenon. 5. A marked increase in Secchi depth in 2000 and declining trends in suspended solids, chlorophyll‐a and total phosphorus concentrations were observed. These changes may also be attributable to changes in the fish community, although the relationships were not straightforward. 6. This 7‐year study indicates that piscivorous fish may be a significant structuring force in shallow eutrophic lakes, suggesting that stocking piscivores can increase predation pressure on cyprinids. However, the general lack of impact of 0+ pike points to the need of refining current stocking practices in several countries across Europe.

A short review of pike ecology

“…by stocking 0+ year pike at [1000 ha -1 to control newly hatched roach and bream Abramis brama (Linnaeus) (Prejs et al, 1994;Berg et al, 1997). There have been extensive experimental studies conducted to determine the optimal conditions for maximizing the impact of these pike stockings, in particular in small eutrophic lakes, for example in Denmark (Skov & Berg, 1999;Skov et al, 2002bSkov et al, , 2003aJacobsen et al, 2004). Many of the in-depth studies on habitat requirements and predator and prey behaviours, as described above, have been carried out as part of these biomanipulation programmes.…”

Relationships between fish feeding guild and trophic structure in English lowland shallow lakes subject to anthropogenic influence: implications for lake restoration

“…Through foraging amongst bottom sediments benthivorous fish may uproot submerged plants (Zambrano and Hinojosa 1999) or cause significant resuspension of fine material, thereby increasing water turbidity and enhancing the release of nutrients into the water column (Breukelaar et al 1994). Piscivorous fish may reduce the density and biomass of prey species (Skov et al 2002), or change their behaviour and habitat use with a potential impact on lower trophic levels (Jacobsen and Perrow 1998).…”

A Comparative Study on the Feeding Competition of the European Perch Perca Fluviatilis L. And the Ruffe Gymnocephalus Cernuus (L.) in Lake Piediluco (Umbria, Italy).

“…Nevertheless, in the meantime, intervention on the structure of the fish community should immediately be undertaken. Bio-manipulation through a stocking programme of piscivorous fish (such as pike, eel and large perch) could contribute to changing the food-web structure by reducing zooplanktivorous and benthivorous fish, thereby lowering trophic levels and ultimately improving water quality (SKOV et al, 2002).…”