Aaron M. Christ Michael B. Wunder Andrew C. Doll Sean D. Farley Lorrie D. Rea David A. S. Rosen R. D. Scherer Dominic J. Tollit Craig A. Stricker 2015 <p><span>Nutritional constraints have been proposed as a contributor to population declines in the endangered Steller sea lion<span class="Apple-converted-space">&nbsp;</span></span><i>Eumetopias jubatus</i><span><span class="Apple-converted-space">&nbsp;</span>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<span class="Apple-converted-space">&nbsp;</span></span><i>in utero</i><span>, potentially offering indirect inference on maternal diet. However, diet reconstruction using isotopic techniques requires<span class="Apple-converted-space">&nbsp;</span></span><i>a priori</i><span><span class="Apple-converted-space">&nbsp;</span>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 &delta;</span>¹³<span>C and averaged 0.8 and 1.6&permil;, respectively, for &delta;</span>¹⁵<span>N. In contrast, vibrissa-fish/invertebrate TEFs averaged 3.3 (&plusmn; 0.3 SD) and 3.7&permil; (&plusmn;0.3) for lipid-free &delta;</span>¹³<span>C and &delta;</span>¹⁵<span>N, respectively. Average lipid-free &delta;</span>¹³<span>C and &delta;</span>¹⁵<span>N vibrissa-milk TEFs were 2.5 (&plusmn;0.9) and 1.8&permil; (&plusmn;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.</span></p> application/pdf 10.3354/meps11205 en Inter-Research Stable carbon and nitrogen isotope trophic enrichment factors for Steller sea lion vibrissae relative to milk and fish/invertebrate diets article