Diet-to-female and female-to-pup isotopic discrimination in South American sea lions

Rationale The use of accurate, species‐specific diet‐tissue discrimination factors is a critical requirement when applying stable isotope mixing models to predict consumer diet composition. Thus, diet‐to‐female and female‐to‐pup isotopic discrimination factors in several tissues for both captive and wild South American sea lions were estimated to provide appropriate values for quantifying feeding preferences at different timescales in the wild populations of this species. Methods Stable carbon and nitrogen isotope ratios in the blood components of two female‐pup pairs and females' prey muscle from captive individuals were determined by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS) to calculate the respective isotopic discrimination factors. The same analysis was carried out in both blood components, and skin and hair tissues for eight female‐pup pairs from wild individuals. Results Mean diet‐to‐female Δ13C and Δ15N values were higher than the female‐to‐pup ones. Pup tissues were more 15N‐enriched than their mothers but 13C‐depleted in serum and plasma tissues. In most of the tissue comparisons, we found differences in both Δ15N and Δ13C values, supporting tissue‐specific discrimination. We found no differences between captive and wild female‐to‐pup discrimination factors either in Δ13C or Δ15N values of blood components. Conclusions Only the stable isotope ratios in pup blood are good proxies of the individual lactating females. Thus, we suggest that blood components are more appropriate to quantify the feeding habits of wild individuals of this species. Furthermore, because female‐to‐pup discrimination factors for blood components did not differ between captive and wild individuals, we suggest that results for captive experiments can be extrapolated to wild South American sea lion populations. Copyright © 2015 John Wiley & Sons, Ltd.