Development of the fish stock and its manageability in the deep, stratifying Wupper Reservoir

Abstract

Today's fish fauna of Wupper Reservoir is the result of natural development in combination with management. Manageability of the fish stock, a prerequisite for continuing biomanipulation, was limited. Despite protection and stocking, the abundance of the stocked predatory fishes (pike, pikeperch) did never exceed 10% of the total fish biomass since filling in 1988. Contrary to predictions, the ''juvenile'' cyclical perch population that became dominant after flooding, with the disappearance of gigantic perch in 1997, was not replaced by cyprinids (460% of total fish biomass). Instead, a strong, non-cyclical piscivorous perch population, plus cyprinids (o40% of total fish biomass) became established, giving rise to low planktivory and high water quality since 1999. There is compelling evidence that the introduction of a self-reproducing pikeperch population was a key-factor in the successful management of this slightly eutrophic reservoir. With the introduction of this new type of predator (pelagic, efficient at low light conditions) there are predators (pikeperch, perch, pike and eel) present in all habitats of the reservoir. Thus, antipredator behaviour of planktivorous perch and roach was enhanced, resulting in substantial habitat segregation. Consequently, the perch were released from competition and became large enough for piscivory. Hence, predator biomass was substantially enhanced, reaching at least 25% of the total fish biomass which was estimated to be in the range of 90 kg ha À1 in August 2003. Ultimately, a high level of piscivory driving the whole lake trophic cascade, and thus a clear-water regime, which seems to be driven and stabilized by internal feed-backs, was established in Wupper Reservoir.

Fish biomass and species composition in the Malta Reservoir, Poland

“…In a long-term biomanipulation experiment stocking with predatory fish (pikeperch, pike, wels and eel) combined with catch restrictions led to the increase of the proportion of piscivores in the total fish biomass from 14 to over 50% and total biomass decrease to about 100 kg·ha -1 (BENNDORF, 1990;1995). Thanks to stocking and predators enhancement the predator biomass have reached at least 25% of the total biomass in the deep, stratifying Wupper Reservoir, including a strong piscivorous perch population (SCHARF, 2008).…”

The use of nutrient reduction and food-web management to improve water quality in the deep stratifying Wupper Reservoir, Germany

“…The fish populations were co-managed to improve both water quality and recreational fisheries (Scharf, 2008). With the damming of the River Wupper northern pike, perch, roach and bream entered the reservoir from its pre-reservoir, which had already been built in 1980.…”

“…Irrespective of their original ichthyofauna, in most Central European reservoirs if roach have penetrated into the reservoir cyprinid dominance is the last stage in the natural development of the fish fauna (Vostradovsky et al, 1989;Kubecka, 1993), even under oligo-/mesotrophic conditions (Scharf, 2007). Therefore, it is reasonable to assume that the fish fauna of Wupper Reservoir, which is built in the grayling zone, without any management would be cyprinid dominated with only a few perch reaching the size of piscivory in the long-term (Scharf, 2008). This implies a general increase in the number of planktivorous fish and a simultaneous increase in the proportion of small water fleas (Bosmina, Daphnia cucullata) in the zooplankton of the reservoir (Vostradovsky et al, 1989), which adversely affects water quality.…”

“…Since development of the predicted cyprinid-dominated fish fauna could be prevented and a strong piscivorous percid-population plus cyprinids built up (Scharf, 2007), both management measures (reduction of nutrient input rates and food-web management), have proved successful in Wupper Reservoir, both independently and consecutively. Nutrient reduction had already been accomplished in 1993, whereas ''top down'' forces started increasing in 1999 (Scharf, 2007(Scharf, , 2008, as indicated by the replacement of the smaller Daphnia cucullata by the larger Daphnia galeata-hyalina complex. In this article, I shall provide results of Wupper Reservoir's response to nutrient load abatement (''bottom up'') in conjunction with reduced zooplanktivory (''top down''), by comparing the reference regime of high nutrient load and high zooplanktivory (1988)(1989)(1990)(1991)(1992) with both a regime of reduced nutrient load plus unchanged, high zooplanktivory (1993)(1994)(1995)(1996)(1997)(1998) and one of unchanged low nutrient load plus reduced zooplanktivory (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006).…”

Long-term changes in the fish community structure revealed by gillnet monitoring in a shallow, lowland reservoir

“…According to Kubečka (1993), under common conditions in central and eastern Europe, six different types of fish fauna can be expected depending on the successional stage of a reservoir; in the case of shallow lowland reservoirs, such as Sulejów Reservoir (Poland), a cyprinid-dominated fish community should be the anticipated mature ichthyocoenoses (Kubečka 1993). Even though this functional faunal type seems to be common and widespread, information about longterm temporal changes in the fish community structure of shallow and nutrient-rich reservoirs is rather scarce and mostly limited to deeper, canyon-shaped reservoirs (Gido et al 2000, Scharf 2008, Říha et al 2009). (Linnaeus, 1758), bream, Abramis brama (Linnaeus, 1758), and white bream, Blicca bjoerkna (Linnaeus, 1758), are the major contributors to cypriniddominated fish communities in combination with a smaller proportion of percids such as perch, Perca fluviatilis Linnaeus, 1758, pike-perch, Sander lucioperca (Linnaeus, 1758), and ruffe, Gymnocephalus cernuus (Linnaeus, 1758).…”