Occurrence and food consumption of the common eider,Somateria mollissima,in the Wadden Sea of Schleswig-Holstein |
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Authors: | Georg Nehls |
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Institution: | 1. Staatliche Vogelschutzwarte, Biologiezentrum, Olshausenstra?e 40-60, D-2300, Kiel, Federal Republic of Germany
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Abstract: | The number of eider in the Wadden Sea of Schleswig-Holstein was counted by aerial surveys during 1986 and 1987. The highest
number occurred during migration in October 1987 with 151 000 ducks, the lowest number during the breeding time in May 1987
with 6000 ducks. About 100 000–120 000 eiders moult in July/August in the Wadden Sea of Schleswig-Holstein, but only 30 000–40
000 stay over winter. The average number was 62 000 ducks. Eider have increased in number since the seventies, when the average
population size was estimated to be only 23 000. The increase referred mainly to moulting and migrating eider, whereas numbers
in winter remained constant. There are substantial changes in the spatial distribution over the year. In most areas sites
used during moult, migration and winter can be clearly separated, although so far no obvious differences in the morphology
of these areas could be found. The annual food consumption was calculated to be 3.1×106 kg AFDW or 1.3 g AFDW×m−2×year−1, which is about 5% of the average biomass of macrozoobenthos. The increase in the number of eider has led to a significant
increase in total food consumption of carnivorous birds, which was estimated at 7.1×106 kg AFDW × year−1 in the seventies and now reaches 9.0×106 kg AFDW×year−1, of which the eider takes 34%. The reasons for and consequences of the increase of the eider are discussed in context with
the eutrophication of the North Sea and possible competition with shellfishery.
Presented at the VI International Wadden Sea Symposium (Biologische Anstalt Helgoland, Wattenmeerstation Sylt, D-2282 List,
FRG, 1–4 November 1988) |
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