Cruz-Vallejo, R.A., F.R., Elorriaga-Verplancken, A.B., Enríquez-García, C.J., Hernández-Camacho, J.C., Herguera-García, R., Moncayo-Estrada, A., Tripp-Valdez & T., Norris (2025). Stable Carbon and Nitrogen Isotope Variation of Guadalupe Fur Seal (Arctocephalus townsendi) Guard Fur and Underfur: Implications for Ecological Interpretations. Aquatic Mammals. 51(6): 448-456. DOI: 10.1578/AM.51.6.2025.448.
Romyna A. Cruz-Vallejo, Fernando R. Elorriaga-Verplancken 1, Arturo B. Enríquez-García, Claudia J. Hernández-Camacho 1, Juan Carlos Herguera-García, Rodrigo Moncayo-Estrada 1, Arturo Tripp-Valdez 1 y Tenaya Norris
The Guadalupe fur seal (Arctocephalus townsendi) has two fur layers (guard fur and underfur) that are usually analyzed as a mixture in stable isotope (d13C and d15N) analyses. Therefore, it is crucial to compare the isotopic composition of fur in these layers to determine whether they grow or are replaced at different rates to guarantee an accurate interpretation of foraging variations assimilated using this tissue. Fur samples were collected from 35 Guadalupe fur seals and separated into layers for subsequent analysis using an isotope ratio mass spectrometer. Given the repeated measures design, differences between fur layers were analyzed using a Bayesian non-centered hierarchical linear model. The guard fur had higher d13C values and lower d15N values than the underfur for all sex and age classes tested. The largest variation was found in d13C, where the differences ranged from ~0.34‰ for adult females to ~1.14‰ for juvenile males. Differences in d15N were more consistent across classes, ranging from approximately -0.83‰ for juvenile males to approximately -1‰ for adult females. The differences in isotopic composition between the two fur layers in the Guadalupe fur seal may result from varying growth and turnover rates and, therefore, may also represent different timeframes. When analyzing fur samples isotopically, it is important to consider this finding for more accurate interpretations regarding the trophic ecology of the species. At minimum, it is crucial to ensure an equal amount of both layers when analyzing mixed fur to yield an average that compares with previous studies.
Palabras clave: Guadalupe fur seals; fur layers; Trophic ecology; Stable isotope analysis
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