Ontogenetic dietary information of the California sea lion (Zalophus californianus) assessed using stable isotope analysis

摘要

We used stable carbon ( 13 C) and nitrogen ( 15 N) isotopes to examine ontogenetic dietary changes in 289 California sea lions (Zalophus californianus) at San Miguel Island, California during 2004–2007. Tissues analyzed included fur, red blood cells, plasma, and serum. For all tissues, pups had higher 15 N values and lower 13 C values compared to adults, which indicated that pups were feeding higher trophically than older conspeci?cs and on a lipid-rich milk diet prior to weaning. Yearling 15 N values were slightly lower than pup or nearly indistinguishable from adult values depending on the tissue analyzed, indicating a dietary shift from maternal dependency to independent foraging. Juveniles (2–4 yr) and adults (>4 yr) had similar 15 N values indicating they fed at a similar trophic level. There did not appear to be a pronounced dietary shift in 13 C values. However, 13 C values integrated with telemetry data indicated that postweaned individuals fed in similar foraging areas. Dietary changes during early life stages may be due to differences in physiology, morphology, experience, or energetic requirements; however, young animals are able to attain the skills needed to consume adult prey types near the end of their second year of life.