Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Because the life cycles of these parasites are complex, predicting the severity of disease in fish requires understanding how life cycles are affected not only by water temperature, nutrient levels and flow, but also by numbers of spores contributed back to the system by infected fish as well as the distribution and abundance of the polychaete host receiving those spores. Data on disease incidence and severity from monitoring of trapped migrating smolts provides the baseline for evaluation of data from other monitoring objectives. The researchers have a variety of tools to determine how these variables affect parasite levels and subsequent disease. A quantitative PCR assay (QPCR)(Hallett and Bartholomew 2006) provides measures of parasites in water samples, in fish or in polychaetes. Sentinel fish studies (Stocking et al. 2006) provide data on disease severity throughout the river and over time. Methods developed for monitoring polychaete populations (Stocking et al. 2006) provides data both on abundance and infection prevalence in that host. These studies are linked to monitoring water quality (Susan Corum, Karuk Tribe; Paul Zedonis, USFWS). By relating information from all of these studies The researchers hope to provide a means to predict disease severity and to provide tools for rapid assessment that would enable decisions to be made on potential pathogen effects. To accomplish these objectives, the researchers have defined a set of locations that will serve as index sites, providing long-term and detailed information on infection in fish and polychaetes, polychaete populations and numbers of parasites in water samples. In 2006, exposures of Klamath River strains of Chinook and coho salmon were included along with disease susceptible rainbow trout to develop correlations between measured parasites in water (a rapid assessment method) and disease outcome. This will be continued in subsequent years to determine disease outcome under what the researchers expect to be different sets of environmental conditions. Developing data sets at identified sites will also allow the researchers to monitor populations of polychaetes in an effort to predict changes that might occur under different environmental conditions and over time. OBJECTIVE 1: Development of a multi-year dataset on infection prevalence in both host populations at selected locations to monitor how changes in flow, temperature and other variables alter parasite infection rate. This objective will provide crucial integration with data from out-migrant populations conducted by USFWS and will address the following research questions: 1. What is the annual variation in disease prevalence and severity in outmigrant Chinook salmon 2. What is the relationship between parasite numbers measured in water samples, infection prevalence in polychaete populations and biological effects in salmon? 3. How do polychaete-parasite populations change (density, abundance, prevalence of infection) and in response to what ecological variables? 4. What are the relative susceptibilities of Chinook and coho salmon and what are their roles in supporting parasite life cycles? OBJECTIVE 2: The goal of this objective is first to create a model to assess the transmission potential of the parasite between the polychaete host and the vertebrate host. Secondly, a community model will be used to examine how this potential is affected by species outside of the transmission cycle and to account for unexpected outcomes that might result from change. The community model allows the researchers to examine how perturbations can affect the basic transmission model. Both together would allow the researchers to do risk analysis following change and to examine the potential for management interventions