COS 243-2 - Prevalence and distribution of two salmonid parasites and their invertebrate host to inform salmon reestablishment post-dam removal.

Abstract: Removing four hydroelectric dams on the Klamath River along the border of Oregon and California is to be the largest dam removal and river restoration project in the world. This project will allow salmon to reach historic spawning grounds for the first time in over 100 years. Understanding salmon disease risk in this area of the river is critical to inform monitoring efforts for salmon reestablishment. In this study, we describe two pathogens of concern, Ceratonova shasta and Parvicapsula minibicornis. These myxozoan parasites are found in rivers throughout the Pacific Northwest and can cause disease in salmonids. They require an invertebrate annelid host to complete their complex life cycle, thus both the density of infected annelids and water borne parasite spores are needed for assessing disease risk.

To investigate the distribution and abundance of both pathogens, we sampled water and annelids. Water was collected directly from the river in three replicates of 1L, filtered to collect spores, and assayed against a standard to quantify spores/L in the water. Annelids were collected from benthic substrates, sorted and counted, then assayed against positive controls to detect infection. Pathogen distribution in water samples differed between parasites and across different sampling sites. High densities of spores in the water did not always correlate to higher infection in the annelid host. Interestingly, although densities of P. minibicornis were higher than C. shasta in water samples, the prevalence of C. shasta was higher in annelid samples. The preliminary results of this study reinforce the complexity of host-parasite relationships and the need for multiple sampling approaches to capture this complexity. The data also provide a pre-dam removal baseline to help inform management efforts for salmon reestablishment post-dam removal.