Diet of red-throated divers Gavia stellata reflects the seasonal availability of Atlantic herring Clupea harengus in the southwestern Baltic Sea |
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| Institution: | 1. Research and Technology Centre Westcoast (FTZ), University of Kiel, Hafentoern 1, D-25761 Buesum, Germany;2. Seestraße 37a, 17429 Seebad Bansin, Germany;1. Molecular Therapeutics/Drug Discovery Program, University of Pittsburgh Cancer Institute, Pittsburgh, PA 15213, USA;2. Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA;3. Department of Pharmaceutical Sciences, University of Pittsburgh School of Pharmacy, Pittsburgh, PA 15213, USA;1. Flathead Lake Biological Station, Wildlife Biology, University of Montana, Missoula, MT, USA;2. Forensic Science and Environmental & Life Sciences Program, Trent University, Peterborough, ON, Canada;1. School of Biological, Earth and Environmental Sciences, University College Cork, Distillery Fields, North Mall, Cork, Ireland;2. ALNILAM Research & Conservation, Cándamo 116, La Berzosa, 28240 Hoyo de Manzanares, Madrid, Spain;3. Sea Mammal Research Unit, Scottish Oceans Institute, University of St Andrews, St Andrews, Fife KY16 8LB, UK;4. Instituto Españolde Oceanografía, Centro Oceanográfico de Vigo, PO Box 1552, 36200 Vigo, Spain;5. Faroese Museum of Natural History, FR-100 Tórshavn, Faroe Islands;6. AZTI Tecnalia, Marine Research Division, Herrera kaia, Portualdea z/g, Pasaia E-20110, Spain;7. Observatoire PELAGIS, UMS 3462 Université de La Rochelle/CNRS, 5 Allées de l''océan, 17000 La Rochelle, France;8. Spanish Cetacean Society, Avda de lasfuerzasarmadas n7, Tarifa, Cadiz 11380, Spain;1. Institute for Terrestrial and Aquatic Wildlife Research, University of Veterinary Medicine Hannover, Büsum, Germany;2. Marine Biological Research Centre, Department of Biology, University of Southern Denmark, Kerteminde, Denmark;3. National Institute of Aquatic Resources, Technical University of Denmark, Kgs. Lyngby, Denmark;4. SDU UAS Center, University of Southern Denmark, Odense, Denmark;5. Max Planck Institute for Ornithology, Seewiesen, Germany;6. Leibniz Institute for Science and Mathematics Education, Kiel, Germany;1. British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK;2. Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Sciencepark 904, 1098 XH Amsterdam, The Netherlands;3. APEM Limited, Suite 2 Ravenscroft House, 59-61 Regent Street, Cambridge CB2 1AB, UK |
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| Abstract: | Red-throated divers are piscivorous seabirds considered to be opportunistic feeders. The overall knowledge about their diet at sea is scarce. A large sample size of 82 by-caught red-throated divers from two winter (2001–02 and 2002–03) and three spring periods (2003, 2004 and 2005) offered the unique opportunity to analyse their dietary composition in the Pomeranian Bight. This area represents a hot spot in their winter distribution in the southwestern Baltic Sea and a marine protected area has been established due to its importance for the divers and other seabird species. Diet composition was analysed based on stomach and gut contents. The comparison of the different prey species was mainly based on reconstructed biomass using regressions between skeletal hard parts such as otoliths and original fish length and weight. The diet of the divers comprised eleven different fish species and nine different families. No interannual differences in the consumption of the nine most important prey species could be observed. However, in contrast to the other fish species the consumption of Atlantic herring and zander differed significantly between seasons. Herring supplied the majority of prey biomass in all three spring periods and zander in both winter periods. Moreover, the average length of herring consumed differed significantly between seasons. In winter, smaller herring was consumed compared to spring. The distinct seasonal changes in the diet composition were paralleled and most probably evoked by the migration pattern of the Western Baltic spring spawning herring which has its main spawning grounds adjacent to the study area. Based on the habitat requirements of the different prey species it could be inferred that mostly the coastal waters of the bight were used for foraging. Its function as spawning, nursery area and feeding ground with numerous resident and migrating fish species available might explain the important role of the Pomeranian Bight as wintering and staging area for red-throated divers in the southwestern Baltic Sea. |
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