Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 174-191). Also available on the World Wide Web.

Thesis (M.S.)--Humboldt State University, 2008. / Includes bibliographical references (leaves 66-69). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 90-96). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2006. / Title from metadata title field (viewed Nov. 13, 2006). Includes bibliographical references (p. 90-96).

Aquatic ecosystems continue to be increasingly affected by climate warming. For salmonids in the Pacific Northwest of North America, increasing temperatures pose tighter thermal constraints on their habitat use as well as aspects of their individual performance, such as disease resistance. This thesis examines the effect of temperature on the phenology of the Ceratomyxa shasta life cycle, the effect of thermal refugia on disease risk in juvenile salmonids in the Klamath River, CA, and the spatial and temporal distribution of C. shasta in the Willamette River, OR. We developed a biological model that predicts an acceleration of the C. shasta life cycle development due to climate shifts in the Klamath River, resulting in more generations per year and earlier seasonal parasite occurrence. We showed that in early summer the Beaver Creek-Klamath River confluence provides juvenile Chinook and coho salmon an area of lower parasite doses and cooler temperatures than the main stem, thus lessening disease risk. By accelerating the development of C. shasta in its hosts, increasing temperatures will result in earlier parasite transmission to juvenile salmonids and a longer season of infectivity. These fish may find disease refuge at cold tributary inflows to the main stem of the Klamath River in early summer, further adding to the benefit of these important thermal habitats. To determine if similar disease patterns occur in other rivers with the parasite, we described spatial and temporal occurrence of C. shasta in the Willamette River. By collecting weekly water sampling at four sites over 28 months we characterize seasonal and annual differences of parasite abundance, which varies with weekly temperature. We also collected samples along the length of the main stem and its tributaries and identified spatial differences in C. shasta spore densities. Identification of spatial and temporal variation of C. shasta in the Willamette River provides a foundation for understanding future patterns of disease occurrence in this river where conservation of anadromous fisheries is also of concern. This thesis identifies likely responses of C. shasta to climate warming in the Klamath River, with useful application to other rivers in the Pacific Northwest. / Graduation date: 2013

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 46-51). Also available on the World Wide Web.

Ceratomyxa shasta infects salmonids in the Pacific Northwest (PNW) of North America, occasionally causing losses in wild and captive populations. Host-specific parasite genotypes (O, I, II, III) were previously characterized molecularly using markers in the ribosomal DNA and phenotypically by type host in the Klamath River, CA/OR. This thesis sough to re-examine the composition of the parasite population elsewhere in the PNW and to further evaluate the host specificity of each genotype. I surveyed salmonids native to the PNW primarily from the Fraser, the Columbia and the Sacramento River basins. I also conducted sentinel studies on the Willamette and Deschutes Rivers that exposed native and non-native salmonids to parasite populations above and below migration barriers. These studies expanded upon the known host range of each genotype: O was specific to rainbow/steelhead (Oncorhynchus mykiss) and coastal cutthroat trout (O. clarkii); I was specific with Chinook salmon (O. tshawytscha); II was non-specific, being detected in six species, but predominating in coho (O. kitsuch), chum (O. keta), and pink (O. gorbuscha) salmon; and III was also non-specific infecting many native and non-native salmonids. Hosts infected with genotype III were considered “adequate” if myxospore development occurred, and included brook char (Salvelinus fontinalis), brown (Salmo trutta), rainbow, cutthroat, and steelhead trout; but Chinook, kokanee/sockeye (O. nerka) and Atlantic salmon (Salmon salar) were less suitable. The distribution, life history, and phylogenetic traits of each salmonid host are factors that potentially explain the host specificity and the spatial and temporal patterns of each genotype. Data collected in this thesis provide evidence that host-specific C. shasta coevolved with Pacific salmonids, adapting unique host-parasite relationships over time. / Graduation date: 2012

The freshwater polychaete Manayunkia speciosa was identified as an obligate host of the salmonid parasite Ceratomyxa shasta in 1997, prompting increased research on the small benthic invertebrate. Ceratomyxa shasta infection in fish can cause mortality, and presents a disease risk for both hatchery and wild salmon and trout. Ceratomyxa shasta is endemic to rivers of the Pacific Northwest, and its effects have been particularly well documented in the Klamath River, Oregon and California. One option for managing C. shasta impacts is by decreasing densities of M. speciosa through habitat manipulation, thus decreasing amplification of the parasite. The Klamath River is regulated by irrigation and hydropower dams, thus manipulating the hydrograph to destabilize habitat is a possibility. Decreasing habitat through flow manipulation requires a thorough understanding of the hydraulic environment of polychaete habitat, and how that environment changes with discharge. This thesis proposes an influence diagram of physical variables driving M. speciosa density, and investigates several of them. Samples were collected for enumerating M. speciosa density from nine sites in the Klamath River over 15 months, and seasonal density changes were examined, as were the relationships between density and hydraulic variables (depth, average velocity, substrate size, Reynolds number, Froude number). Density increased directly with depth and inversely with velocity, and was greater on small (silt, sand) and large (boulder, bedrock) substrate relative to medium substrate (gravel, cobble). Density was highest in the summer (July, August, September), and there was evidence that summer densities were influenced by spring discharges through the mechanism of substrate mobilization. Differences in infection prevalence among seasons and habitats were also investigated; however, very low overall incidence of infection limited any conclusions. Based on these results, it is recommended that habitat modeling for management of M. speciosa populations include a habitat stability component that incorporates s whether peak discharge the previous year surpassed a stability threshold. / Graduation date: 2013