Klamath River Fish Health Studies: Salmon Disease Monitoring and Research. Oregon State University, BOR/USGS Interagency Agreement #R15PG00065 FY2016 April 01, 2016 – March 31, 2017 Annual Report

The myxozoan parasite Ceratonova shasta infects the intestine of salmonid fishes, which can lead to enteronecrosis and mortality. The parasite is endemic to the Pacific Northwest of North America and has been responsible for high mortality in juvenile salmon in the Klamath River basin. Ceratonova shasta cycles between two hosts and two spore stages: waterborne actinospores released from freshwater polychaete worms infect salmonids and develop into myxospores, which are then infectious to polychaetes. The Bartholomew Lab at Oregon State University has been monitoring the spatial and temporal abundance of the parasite in the Klamath River basin since 2006 using sentinel fish exposures, river water sampling, and polychaete sampling. This report describes monitoring studies conducted in 2016. Those data are informing several models being developed to better predict disease effects under various temperature and flow conditions.

Results from polychaete density and infection assays completed in 2016 were remarkably different from those obtained in previous years: Densities decreased at all monitoring sites following the high magnitude flow event in March 2016. Infection prevalence was generally low in 2016 (<1%) which is in contrast to levels observed in 2015 (>1%). However, by late spring (June), densities had begun to increase at river sites downstream IGD including the Seiad Valley and Orleans sites, which are not normally characterized by elevated densities prior to late summer. However, prevalence of infection was high in polychaetes at the Orleans site, resulting in estimates of 5,000-35,000 infected polychaetes m-2. We suggest that polychaetes displaced from reaches below Iron Gate dam during the high magnitude but short duration flood in March settled out at KOR resulting in the relatively high densities detected at this site.