EVALUATING HABITAT USE OF YEARLING CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA) IN THE COLUMBIA RIVER ESTUARY USING TROPHICALLY TRANSMITTED PARASITES
Alison Aceves1, Kym Jacobson2, Laurie Weitkamp2.
1California State University Monterey Bay, Seaside, CA, 2Northwest Fisheries Science Center, National Oceanic and Atmospheric Administration, Newport, OR.
The spring-run Chinook salmon (Oncorhynchus tshawytscha) of the mid/upper Columbia River genetic group are listed as endangered under the Endangered Species Act, and the Columbia River estuary, on the border of Oregon and Washington, serves as an important habitat for subyearling Chinook salmon. However, the extent to which yearlings use and benefit from the estuarine habitats is unclear as they are believed to move rapidly through the estuary. This study examined trophically transmitted parasite assemblages in yearling Chinook salmon to evaluate their use of the estuary for foraging. Salmon were collected with a purse seine from 2 locations in the lower estuary between the years 2007 and 2012. They were examined for tags and clipped adipose fins, measured, and identified to a genetic stock group. Stomach contents were examined by National Oceanic and Atmospheric Administration and Oregon State University researchers for diet. Stomachs and intestines were also examined for trophically transmitted parasites. Preliminary results from 34 mid/upper Columbia River chinook salmon collected in 2007-2009 show these yearling salmon harbor a trophically transmitted parasite community that consists of freshwater and estuarine parasite taxa including trematodes, nematodes, and acanthocephalans. Results suggest interannual variation with higher prevalence of trematodes in 2009 (83%) (n = 12) followed by 2008 (81.8%) (n = 10) and 2007 (25%) (n = 12), and higher prevalence of nematodes in 2007 (58.3%) compared to 2008 (36.4%) and 2009 (8.3%). The overall prevalence of the marine-estuarine parasite species Hysterothylacium aduncum (25%) suggests that yearling chinook salmon are feeding in the Columbia River estuary.