Modelling distribution of common scoter (Melanitta nigra) by its predominant prey, the American razor clam (Ensis leei) and hydrodynamic parameters


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Abstract

The non-breeding distribution of common scoter (Melanitta nigra), which occur in high densities offshore from the eastern Wadden Sea, has been well documented in recent decades, but factors influencing these patterns remain poorly known. We investigated the prey choice of 88 common scoter using stomach contents of beached birds collected over a period of 12 years. We then used benthos data and hydrodynamic parameters to model the June–September distribution patterns during the flightless period of common scoter based on transect count data off the north-eastern German Wadden Sea. Benthic fauna biomass in areas used by common scoter was higher than in areas where the species was absent. American razor clam (Ensis leei) invaded the Wadden Sea during the end of the 1970s and was the most common prey, both in benthos samples from below feeding common scoter and in stomach samples. The relatively high flesh to shell ratio of the American razor clam makes it the most attractive available prey item for common scoter. The abundance of American razor clams explained the distribution of scoter to a high degree, although the best model fit included negative effects of water depth and positive effects of bed shear stress intensity on scoter abundance. Our data show that the neobiotic American razor clams have become an important part of the diet of these sea ducks, whereas the cut trough shell (Spisula subtruncata) was of substantially lesser importance than expected from historical data. Our study shows the ability of a top avian predator to respond to novel developments in bivalve prey availability over periods of a few decades.



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Eprint ID
50064
DOI 10.1016/j.ecss.2019.106260

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Schwemmer, P. , Volmer, H. , Enners, L. , Reimers, H. C. , Binder, K. , Horn, S. , Adler, S. , Fox, A. D. and Garthe, S. , Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761, Büsum, Germany, Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761, Büsum, Germany, Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761, Büsum, Germany, State Agency for Agriculture, Environment and Rural Areas of Schleswig-Holstein, Hamburger Chaussee 25, Flintbek, Germany, State Agency for Agriculture, Environment and Rural Areas of Schleswig-Holstein, Hamburger Chaussee 25, Flintbek, Germany, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Wadden Sea Station Sylt, Hafenstraße 43, 25995, List, Germany, Swedish University of Agricultural Sciences, Department of Forest Resource Management, Division of Landscape Analysis, 901 83, Umeå, Swede, Department of Bioscience, Aarhus University, Grenåvej 14, 8410, Rønde, Denmark, Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761, Büsum, Germany (2019): Modelling distribution of common scoter (Melanitta nigra) by its predominant prey, the American razor clam (Ensis leei) and hydrodynamic parameters , Estuarine Coastal and Shelf Science, 225 . doi: 10.1016/j.ecss.2019.106260


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