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Stable-isotope ratios of blood components from captive northern fur seals (Callorhinus ursinus) and their diet: applications for studying the foraging ecology of wild otariids

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Stable nitrogen and carbon isotope ratios (13C/12C and 15N/14N, respectively) of plasma, serum, clotted red blood cells, and unclotted red blood cells from six captive northern fur seals (Callorhinus ursinus) and two fish species in their diet, Atlantic herring (Clupea harengus) and Icelandic capelin (Mallotus villosus), were measured. The d15N values from the fur seal blood components ranged from 15.5 ± 0.1‰ (mean ± SE; all RBCs) to 16.7 ± 0.1‰ (plasma), and d13C values ranged from –18.3 ± 0.1‰ (serum) to –17.5 ± 0.1‰ (clotted RBCs). Fur seal blood components had higher d15N and d13C values than their diet. Mean enrichments of 15N between fur seal RBCs and plasma/serum and their prey were +4.1 and +5.2‰, respectively, while mean 13C enrichments were +0.6‰ (serum), +1.0‰ (plasma), and +1.3 to +1.4‰ (all RBCs). Fur seal blood components did not differ in d15N or d13C between the sexes. One female (Baabs) was pregnant at the time of sampling and was resampled 4 months later, when she was approximately 3 months post parturient. The d15N values of the blood components taken from Baabs during pregnancy were all higher by 0.6‰ (unclotted RBCs) to 1.3‰ (plasma) than those of samples taken during lactation, while her d13C values were nearly the same (RBCs) for the two time periods or lower during lactation by 0.5‰ (serum) and 0.7‰ (plasma). This study was the first to analyze isotope ratios of blood components from captive fur seals and their prey. The subsequent establishment of fractionation values between captive fur seals and their diet can be used to interpret trophic level and habitat usage of otariids feeding in the wild.

Les rapports des isotopes stables d'azote (15N/14N) et de carbone (13C/12C) ont été déterminés dans le plasma, le sérum, les érythrocytes coagulés et les érythrocytes non coagulés de six otaries à fourrure du Nord (Callo rhinus ursinus) en captivité, ainsi que chez leurs proies, le hareng atlantique (Clupea harengus) et le capelan d'Islande (Mallotus villosus). Les valeurs de d15N dans les composantes du sang de l'otarie à fourrure varient de 15,5 ± 0,1 ‰ (moyennes ± erreur type; tous les érythrocytes) à 16,7 ± 0,1 ‰ (plasma) et celles de d13C, de –18,3 ± 0,1 ‰ (sérum) à –17,5 ± 0,1 ‰ (sang coagulé). Les composantes sanguines de l'otarie à fourrure présentent des valeurs de d15N et de d13C supérieures à celles de leurs proies. Les enrichissements moyens en 15N dans les érythrocytes et le plasma/sérum des otaries par comparaison à leurs proies sont respectivement de +4,1 ‰ et de +5,2 ‰, alors que les enrichissements en 13C sont de +0,6 ‰ dans le sérum, de +1,0 ‰ dans le plasma, et de +1,3 à +1,4 ‰ dans les érythrocytes. Il n'y a pas de différences sexuelles dans les valeurs de

Document Type: Research Article

Publication date: May 1, 2002

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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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