Abstract
For anadromous fish entering the marine environment, we expect the probability of avoiding predation and starvation to increase with the quality and/or quantity of dietary resources consumed during the period immediately prior to, and following, ocean entry. Here, we report the results of research examining trophic history in relation to fork length, mass, and body condition in juvenile Chinook salmon captured in the southern Bering Sea using δ 13 C and δ 15 N analysis of skeletal muscle and liver samples. Our results show little inter-individual variability in δ 15 N, but variability in δ 13 C among tissues and within and among years was observed. Further, we found few relationships between δ 15 N and morphological or condition metrics, but strong relationships between δ 13 C and fork length, body mass, and Fulton’s K. We attribute the similarity in δ 15 N among individuals to high trophic level feeding ( i.e ., piscivory) associated with the prolonged duration of freshwater residency observed for juvenile Chinook salmon in our study area. Variation in δ 13 C, as well as relationships between δ 13 C, fork length, body mass, and Fulton’s K can be attributed to variability in carbon sourcing resulting from the large spatial footprint of our study area. In addition to relating these findings to Chinook salmon ecology, we offer guidance for future use of δ 13 C and δ 15 N analysis in studying early marine trophic interactions in anadromous fish.