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A pilot study examining the effect of adult carcass removal on Ceratomyxa shasta myxospore release was conducted in Bogus Creek, a tributary of the Klamath River, during the fall of 2008. A total of 907 fall-run Chinook salmon carcasses were removed from the lower reach of Bogus Creek (19% of the total Bogus Creek run) while water samples were collected and assayed for C. shasta DNA. Study cooperators included Oregon State University, Yurok Tribal Fisheries, California Department of Fish and Game, and the California Nevada Fish Health Center (FHC). Study results demonstrated that the actinospore stage of the parasite was not present in the creek during the spawning period and thus all parasite detection in water samples was the myxospore stage from the adult salmon.
Overview of study area
The incidence of C. shasta myxospores visually detected in intestinal scrapings of adult salmon was 30%, although molecular detection demonstrated a much higher prevalence of infection. The number of myxospores varied between 3000 and 14.7 million per gram of scraping with no trend for collection date or fish sex. However, decomposed carcasses had higher myxospore loads than fresh carcasses. Results of water sampling conducted concurrently with carcass removal supported the hypothesis that Bogus Creek contributes a significant amount of myxospores to the Klamath River mainstem. During the period of sampling parasite abundance rarely exceeded 1 myxospore/L; however, if this occurred on a sustained basis it would represent a contribution of approximately 57 million spores daily.
Based on this study, we feel that carcass removal from Bogus Creek is logistically feasible and that water filtration can be applied for assessing success. We also recommend a subsequent study on Bogus Creek based on what was learned in 2008, in which the following changes would be made: 1) removal of carcasses could be done weekly rather than daily, 2) water monitoring should be done year-round at the mouth of Bogus Creek, but is only necessary above and below the reach from which carcasses are removed and 3) sentinel exposures no longer are needed as we have multi-year data that the parasite life cycle is not completed in Bogus Creek (i.e. actinospores are not present).
Collection of carcasses of spawned salmon from Bogus Creek
Collection and filtration of water samples
Photo credits: J Strange