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The oystercatcher in the Waddenzee

Compared with the 1980s, the population of oystercatchers in the Waddenzee has plummeted. One possible reason for this is the decline in cockle stocks.

Trends


Between 1975 and 1986 there was an increase in the number of oystercatchers overwintering in the Waddenzee (Wadden Sea), but decline followed, especially after 1995. Current stocks are now 35% below what they were in the 1980s.

One possible reason for the decline is the reduced availability of cockles and mussels, which are the main food for oystercatchers. Research on the differences between areas that are closed to commercial harvesting of shellfish and those where harvesting is allowed has shown that in the latter areas the oystercatchers experience food shortages. Strikingly, cockle numbers have been higher in recent years than they were previously, but not all the cockles are accessible for the birds. The situation is aggravated by the shrinking area of mussel beds exposed at low tide in the Waddenzee.

The oystercatcher has also been declining in the Zeeland delta in recent years. The decline in the food supply in winter in tidal areas seems to be contributing to the decline in the number of breeding oystercatchers throughout the Netherlands.

Technical note


The graph shows the indices for numbers of overwintering oystercatchers, as recorded in 9 subareas in the Waddenzee in January and (where data are available) in the previous autumn. The numbers are running means calculated from three consecutive January and autumn censuses, but excluding the figures in severe winters (1979, 1982, 1985, 1987 and 1997) because in such winters many oystercatchers leave the Waddenzee.

The data are from the Ecological Monitoring Network's waterfowl surveys.

References


  • Philippart, K. en A. Smaal (2000). Schelpdierdynamiek, vogels en visserij in de Waddenzee. Landschap (17) 1: 5-14.
  • Roomen, M. van en C. Smit (2001). In 2000/2001 opnieuw weinig overwinterende scholeksters in Waddenzee. SOVON-nieuws, 14 (3): 12.
  • Smit, C., B. Ens en B. Koks (2000). Afnemende aantallen Scholeksters in de Waddenzee. SOVON-Nieuws, 13 (3): 16-17.

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This page was last changed on 12 May 2004  (version 01).