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Marine Ecology Progress Series

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MEPS 523:255-266 (2015)  -  DOI:

Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets

C. A. Stricker1,*, A. M. Christ2, M. B. Wunder3, A. C. Doll3, S. D. Farley2, L. D. Rea2,4, D. A. S. Rosen5, R. D. Scherer3, D. J. Tollit5,6

1U.S. Geological Survey, Fort Collins Science Center, Denver, CO 80225, USA
2Alaska Department of Fish and Game, Division of Wildlife Conservation, Anchorage, AK 99518, USA
3Department of Integrative Biology, University of Colorado Denver, PO Box 173364, Denver, CO 80217-3364, USA
4Institute of Northern Engineering, University of Alaska Fairbanks, PO Box 755910, Fairbanks, AK 99775-5910, USA
5Marine Mammal Research Unit, University of British Columbia, 2202 Main Mall, Vancouver, British Columbia V6T 1Z4, Canada
6SMRU Canada Ltd, 3069 6th Avenue West, Vancouver, British Columbia V6K 1X4, Canada
*Corresponding author:

ABSTRACT: Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion Eumetopias jubatus in some regions of the North Pacific. Isotopic analysis of vibrissae (whiskers) is a potentially useful approach to resolving the nutritional ecology of this species because long-term (up to 8 yr) dietary information is sequentially recorded and metabolically inert once formed. Additionally, vibrissae are grown in utero, potentially offering indirect inference on maternal diet. However, diet reconstruction using isotopic techniques requires a priori knowledge of trophic enrichment factors (TEFs), which can vary relative to diet quality and among animal species. In this study, we provide new TEF estimates for (1) maternal relative to pup vibrissae during both gestation and nursing and (2) adult vibrissae relative to a complex diet. Further, we refine vibrissa-milk TEFs based on an additional 76 animals with an age distribution ranging from 1 to 20 mo. Mother-pup vibrissae TEF values during gestation and nursing were near zero for δ13C and averaged 0.8 and 1.6‰, respectively, for δ15N. In contrast, vibrissa-fish/invertebrate TEFs averaged 3.3 (± 0.3 SD) and 3.7‰ (±0.3) for lipid-free δ13C and δ15N, respectively. Average lipid-free δ13C and δ15N vibrissa-milk TEFs were 2.5 (±0.9) and 1.8‰ (±0.8), respectively, and did not differ among metapopulations. Empirically determined TEFs are critical for accurate retrospective diet modeling, particularly for evaluating the hypothesis of nutritional deficiency contributing to the lack of Steller sea lion population recovery in some regions of Alaska.

KEY WORDS: Pinniped · Stable isotopes · Fractionation · Diet · Vibrissae

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Cite this article as: Stricker CA, Christ AM, Wunder MB, Doll AC and others (2015) Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets. Mar Ecol Prog Ser 523:255-266.

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