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Combining stable isotope and intestinal parasite information to evaluate dietary differences between individual ringed seals (Phoca hispida botnica)

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The diet and foraging behaviour of nine individual Baltic ringed seals (Phoca hispida botnica Gmelin, 1785) in the Bothnian Bay were studied by combining results from stable isotope analyses (13C and 15N) with data on intestinal parasites whose occurrence varied among the fish hosts. The patterns of infection with three acanthocephalan parasites, Corynosoma semerme (Forssell, 1904), Corynosoma magdaleni Montreuil, 1958, and Corynosoma strumosum (Rudolphi, 1802), and with a cestode larva, Schistocephalus solidus (Müller, 1776), were examined. The ringed seals become infected with these intestinal parasites by feeding on the fish hosts and hence have different parasite species and different parasite burdens according to their dietary history. 13C and 15N values were determined from diaphragm muscle of the seals and from tissues of potential prey items. A dual isotope plot of 13C and 15N values for individual seals and mean values for key potential prey species, together with the parasitological data from the seals, allowed inferences to be drawn about the feeding of individual seals. It appeared that two seals foraged particularly on fourhorn sculpin (Myoxocephalus quadricornis (L., 1758)) and one seal consumed a high proportion of the isopod Saduria entomon (L., 1758). Three seals apparently preferred coastal benthic prey in their diets, while two other seals fed more on pelagic herring (Clupea harengus membras L., 1761). One older female seal evidently also fed on salmon (Salmo salar L., 1758).

Nous avons étudié le régime alimentaire et le comportement de recherche de nourriture chez neuf phoques de la Baltique (Phoca hispida botnica Gmelin, 1785) de la baie de Botnie en combinant les résultats d'analyses d'isotopes stables (13C et 15N) avec des données sur les parasites intestinaux dont l'occurrence varie d'un poisson-hôte à un autre. Nous avons examiné les patrons d'infection de trois acanthocéphales parasites, Corynosoma semerme (Fossell, 1904), Corynosoma magdaleni Montreuil, 1958 et Corynosoma strumosum (Rudolphi, 1802) et d'une larve de cestode Schistocephalus solidus (Müller, 1776) chez les phoques. Les phoques de la Baltique s'infectent avec ces parasites intestinaux en se nourrissant des poissons-hôtes des parasites; ils possèdent donc différentes espèces de parasites et des charges parasitaires différentes en fonction de leur histoire alimentaire. Nous avons déterminé les valeurs de 13C et de 15N dans le muscle du diaphragme de ces mêmes phoques et dans les tissus des différentes proies potentielles. Un graphique isotopique double des valeurs de 13C et de 15N pour les phoques individuels et des valeurs moyennes des principales espèces de proies potentielles, combiné aux données parasitologiques des mêmes phoques, permet de déduire l'alimentation des phoques individuels. Il semble que deux phoques se soient alimentés principalement de chaboisseaux à quatre cornes (Myoxocephalus quadricornis (L., 1758)) et qu'un autre ait consommé en grande proportion des isopodes Saduria entomon (L., 1758). Trois phoques préfèrent apparemment les proies côtières/benthiques dans leur régime et deux autres se nourrissent plus de harengs (Clupea harengus membras L., 1761) pélagiques. Une phoque femelle plus âgée s'est de toute évidence nourrie de saumon (Salmo salar L., 1758).

Document Type: Research Article

Publication date: 2006-06-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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