Feeding ecology of juvenile rockfishes off Oregon and Washington based on stomach content and stable isotope analyses

The feeding habits of pelagic, juvenile rockfishes (Sebastes spp.) collected off Oregon in 2002, and Oregon and Washington in 2006, were examined using stomach content and stable isotope analyses. Sampling occurred along a series of transects across the shelf between Crescent City, California (Lat. 41A degrees 54.0'), and Newport, Oregon (Lat. 44A degrees 39.0'), in 2002, and off Willapa Bay, Washington (Lat. 46A degrees 40.0'), and the Columbia River, Oregon (Lat. 46A degrees 10.0'), in 2006. Species composition varied both years with distance from shore, but the predominant species were darkblotched (Sebastes crameri), canary (S. pinniger), yellowtail (2006 only; S. flavidus), and widow (S. entomelas) rockfishes. Stomach content analysis revealed that darkblotched rockfish had highly variable diets, and canary, yellowtail, and widow rockfishes exhibited a high degree of overlap in 2006. Multivariate analysis showed significant differences in diet based on distance from shore where caught, fish size, and species. Stable isotope analysis indicated that all species were feeding at about the same trophic level within each year, with a 1.5 aEuro degrees difference in delta N-15 between years and regions. The difference in delta N-15 values may indicate a greater contribution of mesotrophic zooplankton such as euphausiids, hyperiid amphipods, and chaetognaths to fish diets in 2006. Depleted C-13 values were indicative of diets based on primary production from a more offshore origin, suggesting that these rockfish had previously inhabited offshore waters. These results add to our understanding of some of the important environmental factors that affect young-of-the-year rockfishes during their pelagic phase.