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Bream and the water quality of the Veluwemeer

The water quality in the marginal lakes of the IJsselmeerpolders has improved, thanks in part to the fishing of bream, a species which churns up the bottom sediment.

Trends


After the bream arrived in the Veluwemeer (lake Veluwe) in the late 1960s it multiplied rapidly, reaching an average density of 100 -120 kg/ha. The large fluctuations in bream numbers in the 1970s and 1980s reflect natural variation in the number of young bream. Since 1995 the density has been consistently lower. This decline is the result of commercial fishery: since 1993 commercial fishermen have been intensively fishing for bream, because of the favourable market for this fish and the decline in eel catches.

When searching for food, bream churn up the lake bottom, making the water turbid. The decline in bream since 1995 has resulted in clearer water, a change helped by the abatement of discharges of nutrients into the Veluwemeer and by an increase in the numbers of zebra mussel, a species that filters the water. The clearer water has led to an increase in duckweed and in fish species other than bream; in turn, there has been an increase in the birds that eat fish and duckweed.

Technical note


The figure shows trends in the bream population as determined by the Regionale Directie IJsselmeergebied of the Directorate-General of Public Works and Water Management. The sampling was conducted using bag-shaped nets suspended between two boats and dragged over the lake bed.

References


  • Lammens, E.H.R.R. (1986). Interactions between fishes and the structure of fish communities in Dutch shallow eutrophic lakes. Ph.D.Thesis. Wageningen University.
  • Meijer, M.L. (2000). Biomanipulation in the Netherlands. 15 years of experience. PhD.Thesis. Wageningen University.
  • Meijer, M.L, R. Portielje, R. Noordhuis, W. Joosse, M. van der Berg, B. Ibelings, E. Lammens, H. Coops en D.T.van der Molen (1999). Stabiliteit van de Veluwerandmeren. BOVAR-rapportnummer 99.06. RIZA-rapport 99.054. Lelystad.
  • Steinmetz, B., E.H.R.R. Lammens en W.L.T. van Densen (1990). Management problems with the different allocations of fishing rights to sport and commercial fishermen in the Frisian lakes, The Netherlands. In: Proceedings of a symposium organized by the European Inland Fisheries Advisory Commission, Goteborg, Sweden, 31 May-3 June 1988. PUDOC. Wageningen.

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This page was last changed on 06 May 2004  (version 01).