Spatial, temporal, age, and sex related variation in the diet of South American sea lions in southern Chile

We analyzed spatial, temporal, and age/sex variation in the diet of the South American sea lions (SASL, Otaria byronia) in southern Chile via C-13 and N-15 isotope analysis, with emphasis on exotic farmed and feral salmonids as a source of prey for this generalist predator. Isotope mixing models show that the primary prey consumed by SASL were demersal and benthopelagic fishes. Individuals sampled in summer and in the outer coast had higher N-15 values than those from winter or from the inner coast due to consumption of high trophic level demersal fish. We also found evidence of an ontogenetic shift in isotopic niche width as measured by C-13 and N-15 standard ellipse areas, with juveniles showing a restricted isotopic niche width (1.0 parts per thousand(2)) in comparison to subadult (2.2 parts per thousand(2)) and adult males (1.9 parts per thousand(2)). The proportion of salmonids in the diet of the SASL was negligible and lower than reported in previous studies, which may be related to a recent drop in the production of salmon aquaculture in the region. Our study suggests that the SASL are able to adapt to shifts in spatiotemporal variations in the abundance of potential prey, including feral and farmed salmonids.