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Variation in winter diet of southern Beaufort Sea polar bears inferred from stable isotope analysis

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Abstract:

Ringed seals (Phoca hispida Schreber, 1775 = Pusa hispida (Schreber, 1775)) and bearded seals (Erignathus barbatus (Erxleben, 1777)) represent the majority of the polar bear (Ursus maritimus Phipps, 1774) annual diet. However, remains of lower trophic level bowhead whales (Balaena mysticetus L., 1758) are available in the southern Beaufort Sea and their dietary contribution to polar bears has been unknown. We used stable isotope (13C/12C, 13C, 15N/14N, and 15N) analysis to determine the diet composition of polar bears sampled along Alaska’s Beaufort Sea coast in March and April 2003 and 2004. The mean 15N values of polar bear blood cells were 19.5‰ (SD = 0.7‰) in 2003 and 19.9‰ (SD = 0.7‰) in 2004. Mixing models indicated bowhead whales composed 11%–26% (95% CI) of the diets of sampled polar bears in 2003, and 0%–14% (95% CI) in 2004. This suggests significant variability in the proportion of lower trophic level prey in polar bear diets among individuals and between years. Polar bears depend on sea ice for hunting seals, and the temporal and spatial availabilities of sea ice are projected to decline. Consumption of low trophic level foods documented here suggests bears may increasingly scavenge such foods in the future.

Les phoques marbrés (Phoca hispida Schreber, 1775= Pusa hispida (Schreber, 1775)) et les phoques barbus (Erignathus barbatus (Erxleben, 1777)) constituent la plus grande partie du régime alimentaire annuel de l’ours polaire (Ursus maritimus Phipps, 1774). Il y a cependant des restes de baleines franches boréales (Balaena mysticetus L., 1758), un animal de niveau trophique inférieur, disponibles dans le sud de la mer de Beaufort; leur contribution au régime des ours polaires est inconnue. Nous avons utilisé une analyse des isotopes stables (13C/12C, 13C, 15N/14N et 15N) afin de déterminer la composition du régime alimentaire des ours polaires dans la mer de Beaufort, le long de la côte d’Alaska, en mars et avril 2003 et 2004. Les valeurs moyennes de 15N des érythrocytes d’ours polaires étaient de 19,5‰ (ET = 0,7‰) en 2003 et de 19,9‰ (ET = 0,7‰) en 2004. Des modèles de mélange indiquent que les baleines franches boréales représentent 11%– 26% (IC de 95%) du régime alimentaire des ours polaires échantillonnés en 2003 et 0%– 14% (IC de 95%) en 2004. Cela révèle une importante variation entre les individus et les années dans la proportion des proies de niveau trophique inférieur dans le régime alimentaire des ours polaires. Les ours polaires utilisent la banquise pour la chasse au phoque et on prédit une diminution de la disponibilité temporelle et spatiale de la banquise dans le futur. La consommation de nourriture de niveau trophique inférieur observée ici laisse croire que les ours risquent de plus en plus de se servir de telles charognes dans l’avenir.

Document Type: Research Article

Publication date: May 1, 2007

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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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