Pacific salmon (Oncorhynchus spp.) early marine feeding patterns based on 15N/14N and 13C/12C in Prince William Sound, Alaska

Nitrogen and carbon mass and stable isotope composition among cohorts of Pacific salmon (Oncorhynchus spp.) released from Prince William Sound, Alaska, hatcheries in 1994 varied widely, suggesting a range in early marine feeding patterns. Analyses consisted of whole-body stable carbon and nitrogen mass and stable isotope composition of selected release-date cohorts that had been identified by implanted coded wire tags (CWT). Nitrogen isotopic and mass shifts suggested that the initial protein pool within individual fish was replaced at different rates among cohorts. There was a notable difference in carbon source dependency among hatcheries. Salmon from the hatchery closest to the Gulf of Alaska had a 13C-depleted carbon signature consistent with Gulf carbon, whereas salmon from the other hatcheries had Sound signatures. Differences in early marine feeding histories among 1994 hatchery-release-date cohorts reconstructed from the stable isotope composition of fry bore no relationship to marine survival pattern. Varied survival rates of 1994 Prince William Sound hatchery salmon were more likely related to the fry size at time of release, the observed differences in growth rate among release cohorts, and predation refuge effects of pen-rearing.