Individual study: Development of fish communities after biomanipulation in Bleiswijkse Zoom, Zuid Holland, the Netherlands
, Lammens E.H.R.R., Raat A.J.P., Klein Breteler J.G.P. & Grimm M.P. (1995) Development of fish communities in lakes after biomanipulation. Aquatic Ecology, 29, 91-101
In order to restore lakes affected by eutrophication in the Netherlands, as a follow-up to reducing nutrient loading (primarily due to agricultural run-off), biomanipulation (i.e. fish stock reduction, and sometimes introduction of native piscivorous fish) has been undertaken. In three small shallow lakes (Noorddiep, Bleiswijkse Zoom and Zwemlust) nutrient reduction measures resulted in clear water and re-establishment of submerged macrophytes. However, fish communities developed differently. Here, development of fish communities at Bleiswijkse Zoom after initial restoration efforts, are presented.
Study site: Lake Bleiswijkse Zoom in Zuid Holland, western Netherlands, comprises three interconnected lakes (total length 2 km; area 14.4 ha; average depth 1.1 m). Subsequent to carp Cyprinus carpio stocking (1973-1974 and 1980-1982), during 1980-1987 the lake developed high nutrient concentrations and turbid water, and submerged macrophytes disappeared.
After initial restoration (nutrient reduction) in 1988/1989, water transparency greatly increased, algae were much reduced and macrophytes re-established (for further details see: www.conservationevidence.com/ViewEntry.asp?ID=1426).
Fish biomanipulation: The waterbody was divided into two parts by a dam (with a gauze covered opening allowing exchange of water, but not of fish). From one part fish were removed: about 80% of the fish stock removed in spring 1987, and pikeperch Stizostedion lucioperca fingerlings (with low subsequent survival) added in an attempt to regulate planktivorous fishes. Pike Esox lucius (from 1988 onwards) were added as the population was almost zero due to the previously turbid water conditions. The other part of the lake served as a control.
Fish monitoring: In both sections fish were monitored (up to 1992 presented here). The density of each species was estimated by mark-recapture, and density was converted to biomass. Small cyprinids could not be marked, thus their estimated biomass was based on the seine-net catches.
Before removal in 1987, the fish stock was about 760 kg/ha (>90% bream Abramis brama and carp). After reduction to c.100 kg/ha, bream and carp biomass increased to c. 250 kg/ha in 1991, despite further reductions in 1988 (90 kg/ha removed) and 1989 (100 kg/ha removed); roach Rutilus rutilus, rudd Scardinius erythrophthalmus and perch Perca fluviatilis also increased in density. Compared to the control, fish biomass was only a little lower, but in the treatment area there were more species. Bream and carp declined and were partly replaced by roach and perch.
The biomass of piscivorous fish did not change, but pike-perch was replaced by pike and perch. Pike increased (by growth, natural reproduction and stocking) from almost zero to 20 kg/ha and piscivorous perch from zero to 17 kg/ha. Despite this, pike and perch did not control young-of-the-year cyprinids, which reached a much higher biomass than in the control area; recruitment was similar or higher in the clear water areas with macrophytes than in the turbid water before restoration.
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