Mixing models using stable isotope data are valuable tools for inferring the diet of wild animal populations that are of conservation concern or difficult to study. Application of mixing models requires the use of trophic discrimination factors. The Cook Inlet stock of beluga whales ( Delphinapterus leucas (Pallas, 1776)) is endangered and there is interest in using stable isotopes to study their diet, however, there are no trophic discrimination factors determined specifically for beluga whales. Using three beluga whales fed a known diet under professional human care, we provide trophic discrimination factors for δ 13 C and δ 15 N values in beluga skin (Δ 13 C: 1.3 ± 0.7, delipidated Δ 13 C: 0.0 ± 0.7, Δ 15 N: 2.8 ± 0.5), red blood cells (Δ 13 C: 1.5 ± 0.6, delipidated Δ 13 C: 0.3 ± 0.7, Δ 15 N: 2.1 ± 0.5), and serum (Δ 13 C: 1.1 ± 0.6, delipidated Δ 13 C: −0.2 ± 0.6, Δ 15 N: 2.9 ± 0.3). A mixing model using our trophic discrimination factors for skin better estimated the known diet compared with models using trophic discrimination factors from the literature, demonstrating that using trophic discrimination factors determined for other species can lead to inaccurate mixing model outcomes. The beluga-specific trophic discrimination factors determined in this study are applicable to future diet studies of belugas.
Olnes et al. (Thu,) studied this question.