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. 41°54.0′), and Newport, Oregon (Lat. 44°39.0′), in 2002, and off Willapa Bay, Washington (Lat. 46°40.0′), and the Columbia River, Oregon (Lat. 46°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 ‰ difference in δ¹⁵N between years and regions. The difference in δ¹⁵N values may indicate a greater contribution of mesotrophic zooplankton such as euphausiids, hyperiid amphipods, and chaetognaths to fish diets in 2006. Depleted ¹³C 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

Survey of Pathogens in Hatchery Chinook Salmon with Different Out-Migration Histories through the Snake and Columbia Rivers

The operation of the Federal Columbia River Power System (FCRPS) has negatively affected threatened and endangered salmonid populations in the Pacific Northwest. Barging Snake River spring Chinook salmon Oncorhynchus tshawytscha through the FCRPS is one effort to mitigate the effect of the hydrosystem on juvenile salmon out-migration. However, little is known about the occurrence and transmission of infectious agents in barged juvenile salmon relative to juvenile salmon that remain in-river to navigate to the ocean. We conducted a survey of hatchery-reared spring Chinook salmon at various points along their out-migration path as they left their natal hatcheries and either migrated in-river or were barged through the FCRPS. Salmon kidneys were screened by polymerase chain reaction for nine pathogens and one family of water molds. Eight pathogens were detected; the most prevalent were Renibacterium salmoninarum and infectious hematopoietic necrosis virus. Species in the family Saprolegniaceae were also commonly detected. Pathogen prevalence was significantly greater in fish that were barged through the FCRPS than in fish left to out-migrate in-river. These results suggest that the transmission of infectious agents to susceptible juvenile salmon occurs during the barging process. Therefore, management activities that reduce pathogen exposure during barging may increase the survival of juvenile Chinook salmon after they are released.Keywords: Oncorhynchus tshawytscha, Pacific Northwest, hatchery, pathogens, juvenile

Ecology and early life history of BATHYNERITA NATICOIDEA: evidence for long-distance larval dispersal of a cold seep gastropod

OIMB MS ThesisA print copy of this title is available through the UO Libraries under the call number: SCIENCE QL430.5.N5 V83 200

Assimilation Efficiency of PBDE Congeners in Chinook Salmon

Polybrominated diphenyl ether (PBDE) flame retardants are environmental contaminants that can accumulate in biota. PBDE accumulation in an organism depends on exposure, assimilation efficiency, and elimination/metabolism. Net assimilation efficiency represents the fraction of the contaminant that is retained in the organism after exposure. In the present study, congener-specific estimates of net PBDE assimilation efficiencies were calculated from dietary exposures of juvenile Chinook salmon. The fish were exposed to one to eight PBDE congeners up to 1500 ng total PBDEs/g food. Mean assimilation efficiencies varied from 0.32 to 0.50 for BDE congeners 28, 47, 99, 100, 153, and 154. The assimilation efficiency of BDE49 was significantly greater than 100%, suggesting biotransformation from higher brominated congeners. Whole body concentrations of BDE49 significantly increased with both exposure to increasing concentrations of BDE99 and decreasing fish lipid levels, implying lipid-influenced debromination of BDE99 to BDE49. Excluding BDE49, PBDE assimilation efficiency was not significantly related to the numbers of congeners in the diets, or congener hydrophobicity, but was greater in foods with higher lipid levels. Estimates of PBDE assimilation efficiency can be used in bioaccumulation models to assess threats from PBDE exposure to Chinook salmon health and recovery efforts, as well as to their predators