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Marine Ecology Progress Series

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MEPS 263:287-298 (2003)  -  doi:10.3354/meps263287

Marine mammals from the southern North Sea: feeding ecology data from δ13C and δ15N measurements

K. Das1,2,*, G. Lepoint1, Y. Leroy1, J. M. Bouquegneau1

1Marine Research Center (MARE), Laboratory for Oceanology, University of Liège, B6c, Sart-Tilman, 4000 Liège, Belgium
2Forschung- und Technologiezentrum Westkueste, Werftstrasse 6, 25761 Büsum, Germany

ABSTRACT: The harbour porpoise Phocoena phocoena, grey seal Halichoerus grypus, harbour seal Phoca vitulina and white-beaked dolphin Lagenorhynchus albirostris are regularly found stranded along southern North Sea coasts. Occasionally, offshore species such as the fin whale Balaenoptera physalus, the white-sided dolphin L. acutus and the sperm whale Physeter macrocephalus are also found stranded. In order to trace their diet, we measured δ13C and δ15N in their muscles as well as in 49 invertebrate and fish species collected from the southern North Sea. The δ15N data indicate that the harbour seal, grey seal and white-beaked dolphin occupy the highest trophic position, along with ichtyophageous fishes such as the cod Gadus morhua (mean muscle values of 18.7, 17.9, 18.8 and 19.2‰ respectively). The harbour porpoise occupies a slightly lower trophic position (mean δ15N value of 16.2‰), reflecting a higher amount of zooplanktivorous fishes in its diet (mean δ15N of 14.7‰); 2 suckling harbour porpoises displayed a significant δ15N enrichment of 2.2‰ compared to adult females. Adult females are δ15N-enriched compared to adult male harbour porpoises. Fin whales, sperm whales and white-sided dolphins are 13C-depleted compared to southern North Sea particulate organic matter and species, suggesting that despite regular sightings, they do not feed within the southern North Sea area.

KEY WORDS: North Sea · Marine mammals · Stable isotopes · Food web

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