Individual study: Development of fish communities after biomanipulation in Noorddiep, Gelderland, 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), major fish stock reduction and introduction of young pike Esox lucius (pike having declined or extirpated due to poor water conditions) has sometimes been undertaken. In three small shallow lakes (Noorddiep, Bleiswijkse Zoom and Zwemlust) nutrient reduction measures resulted in a clear water and re-establishment of submerged macrophytes. Here, development of fish communities at Noorddiep after initial restoration, are presented.
Study site: Noorddiep (average depth 1.5m), prior to nutrient loading reduction, had high nutrient concentrations; the Secchi disc transparency of the water was low (0.2-0.3 m) and algal biomass was high.
Fish stock manipulation: The lake was divided into two: from one part (surface area 4.5.ha) fish were removed, the other part served as a no fish stock reduction 'control' (11.1 ha;). Exchange of water (via a gauze-covered barrier) was possible between the sections, but not of fish. In March 1988, 545 kg/ha of fish were removed and a further 39 kg/ha in November (i.e. about 80% of the total fish stock); no pike were added as a reasonable population was present.
Monitoring: After reduction, biomass and fish composition were monitored during five years. The density of fish was estimated by mark-and-recapture, and density was converted to biomass. Young-of-the-year cyprinids could not be marked, thus their estimated biomass was based on seine-net catches.
Macrophytes: Macrophyte cover was determined by a survey in the summer.
In the first year after fish removal, the water became transparent to the lake bottom, macrophyte cover increased from 30% to 65% and the fish community became more diverse. Bream Abramis brama and carp Cyprinus carpio remained at a reduced stable level c. 100 kg/ha. Roach and perch increased from c. 50-75 kg/ha to 100-150 kg/ha in 1991-1992. Compared with the control section, total fish biomass decreased by about 66%. Pike-perch Stizostedion lucioperca was replaced by pike (biomass increasing from c. 15 to 30 kg/ha) and piscivorous perch (6 to 20 kg/ha).
Total biomass of planktivorous young of the year in both lake sections was similar, but composition changed: perch and roach increased from 10% (roach and perch equally present) in the control to 84% in the removal section (70% O+ perch, 14% O+ roach); total planktivorous fish stock was lower in the removal section.
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