ENS B J, E A J VAN WINDEN, C A M VAN TURNHOUT, M W J VAN ROOMEN, C J SMIT & J M JANSEN (2009) Changes in the abundance of intertidal birds in the Dutch wadden Sea in 1990-2008: differnces between East and West. LIMOSA 82 (3): 100-112.

This paper investigates the changes in the numbers of waders using the Dutch Wadden Sea since 1990, when intertidal stocks of cockles Cerastoderma edule and mussels Mytilus edulis reached an all-time low due to overfishing. Following the collapse of the intertidal shellfish beds, these beds were better protected and shellfish stocks increased again. However, this recovery was restricted to the eastern part of the Dutch Wadden Sea, whereas stocks of shellfish showed no trend in the western part, or even declined, as did Baltic tellin Macoma balthica (Fig. 2). As expected, trends of shellfish-eating birds differed between the western and the eastern parts of the Dutch Wadden Sea (Tab. 1, Fig. 4-6). Red Knot Calidris canutus and Common Eider Somateria mollissima declined in the western Dutch Wadden Sea and increased in the eastern part. Herring Gull Larus argentatus declined in both areas, but the decline was more marked in the western part. Surprisingly, Oystercatcher Haema - topus ostralegus strongly declined in both parts of the Dutch Wadden Sea. The absence of a clear difference between the trends in the two parts may be linked to the extreme longevity and site faithfulness of this species, as well as hand cockle fishery. Some of the bird species that do not feed on shellfish but on prey living on or in shellfish beds also showed a decline in the western and an increase in the eastern Dutch Wadden Sea. This was especially clear for Turnstones Arenaria interpres. Species feeding predominantly on worms increased in both parts, but the trend was more marked for the western Dutch Wadden Sea. Whereas the trend of shellfish-eating species was reasonably explained by a change in food abundance (itself probably linked to both eutrophication and shellfish fishery), it is at present not clear what factors are primary responsible for the trends in wormeating species. Candidates include shellfish fishery, climate change and eutrophication. These hypotheses are not mutually exclusive and future research should focus on determining the relative importance of each of these hypotheses and how they interact.

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