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

To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by Springer and can be found at: http://link.springer.com/journal/227.The feeding habits of pelagic, juvenile rockfishes\ud (Sebastes spp.) collected off Oregon in 2002, and Oregon\ud and Washington in 2006, were examined using stomach\ud content and stable isotope analyses. Sampling occurred\ud along a series of transects across the shelf between Crescent\ud City, California (Lat. 41°54.0′), and Newport, Oregon (Lat.\ud 44°39.0′), in 2002, and off Willapa Bay, Washington (Lat.\ud 46°40.0′), and the Columbia River, Oregon (Lat. 46°10.0′),\ud in 2006. Species composition varied both years with distance\ud from shore, but the predominant species were darkblotched\ud (Sebastes crameri), canary (S. pinniger), yellowtail\ud (2006 only; S. flavidus), and widow (S. entomelas) rockfishes.\ud Stomach content analysis revealed that darkblotched\ud rockfish had highly variable diets, and canary, yellowtail,\ud and widow rockfishes exhibited a high degree of overlap in\ud 2006. Multivariate analysis showed significant differences\ud in diet based on distance from shore where caught, fish\ud size, and species. Stable isotope analysis indicated that all species were feeding at about the same trophic level within\ud each year, with a 1.5 ‰ difference in δ¹⁵N between years\ud and regions. The difference in δ¹⁵N values may indicate a\ud greater contribution of mesotrophic zooplankton such as\ud euphausiids, hyperiid amphipods, and chaetognaths to fish\ud diets in 2006. Depleted ¹³C values were indicative of diets\ud based on primary production from a more offshore origin,\ud suggesting that these rockfish had previously inhabited\ud offshore waters. These results add to our understanding\ud of some of the important environmental factors that affect\ud young-of-the-year rockfishes during their pelagic phase