Artikel: Eidereendensterfte veroorzaakt door schelpdiervisserij

Het onderstaande artikel is een samenvatting van een artikel dat binnenkort verschijnt in het internationale wetenschappelijke tijdschrift Biological Conservation. Het onderzoek is uitgevoerd door een groep wetenschappers afkomstig van de Universiteiten Groningen en Rotterdam, het Nederlands Instituut voor Onderzoek der Zee (NIOZ), Alterra en Rijkswaterstaat (RIKZ). Conclusies:

1) In de winter van 2000 stierven er 21.000 Eidereenden in de Waddenzee.

2) Deze sterfte kan niet door parasieten veroorzaakt. De hoeveelheid parasieten in de verhongerde Eiders waren niet hoger dan normaal.

3) Eidereenden hebben minimaal 3.1 miljoen kg kokkels en mossels nodig om te kunnen overwinteren.

4) na de mechanische schelpdiervisserij van de afgelopen tien jaar was er de hele Waddenzee nog maar 14,5 miljoen kg over, waarvan een groot gedeelte niet beschikbaar is omdat het of te diep zit, bewaakt wordt door mosselkwekers of al door andere soorten vogels als Scholeksters is opgegeten.

5) De hoofdoorzaak van de sterfte is dan ook verhongering door voedselgebrek, hoogstwaarschijnlijk veroorzaakt door overbevissing.

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Article in press: Biological Conservation

Received 25 June 2001; received in revised form 1 November 2001; accepted 9 November 2001

Mass mortality of common eiders (Somateria mollissima) in the Dutch Wadden Sea, winter 1999/2000: starvation in a commercially exploited wetland of international importance

C.J. Camphuysen (a,b),, C.M. Berrevoets (c), H.J.W.M. Cremers (d), A. Dekinga (b), R. Dekker (b), B.J. Ens (e), T.M. van der Have (f), R.K.H. Kats (e,g), T. Kuiken (h), M.F. Leopolde, J.van der Meerb, T.Piersma (b,g

Abstract

Mass mortality of common eiders (Somateria mollissima) was observed in winter 1999/2000 in the Dutch Wadden Sea. Approximately 21,000 common eiders died.

Dissected birds were severely emaciated and 94% were infected with the acanthocephalan parasite Profilicollis botulus. Green shore crabs (Carcinus maenas), intermediate hosts of the parasite, were slightly more ‘available’ than in other years, but parasite infections in the eiders were close to normal. Few eiders were oiled (5%), there were no toxicological, bacteriological, or virological explanations for the observed mortality.

In the Wadden Sea , a wetland of international importance, mussel (Mytilus edulis) cultures occur in sublittoral areas, while mechanical cockle (Cerastoderma edule) fisheries are licensed annually after evaluation of available resources. The wintering eiders in 1999/2000 required c. 3.1 million kg ash-free dry mass, while information on mussel and cockle stocks (irrespective of accessibility and profitability) suggested a resource 4.7 x the requirement of common eiders only. Food shortage is suggested to have caused the observed mortality, involving both principal (mussels and cockles) and secondary (Spisula) prey.

Winter census reports showed shifts in wintering distribution of common eiders in the 1990s, indicating the utilisation of Spisula in the North Sea in poor food years in the Wadden Sea. Following particularly intense fisheries in summer 1999, attempts to feed on Spisula in winter 1999/2000 failed. It is hypothesised that overfishing of mussels and cockles in the Wadden Sea in the early 1990s resulted in structurally reduced food resources, contractions of the foraging area of common eiders, and increased use of secondary prey in the North Sea.

a) CSR Consultancy, Ankerstraat 20, 1794 BJ Oosterend, Texel, The Netherlands; b) Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1790 AB Den Burg, Texel, The Netherlands; c) Rijksinstituut voor Kust en Zee, PO Box 8039, 4330 EA Middelburg, The Netherlands; dDr H. Th. s'Jacoblaan 62, 3571 BN Utrecht, The Netherlands; e) Alterra, PO Box 167, 1790 AD Den Burg, Texel, The Netherlands; f) Vogelbescherming Nederland, PO Box 925, 3700 AX Zeist, The Netherlands; g) Centre for Ecological and Evolutionary Studies, Zoological Laboratory, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands; h) Department of Virology, Erasmus University, PO Box 1738, 3000 DR Rotterdam, The Netherlands