Deschutes River Subbasin Ceratanova Shasta Presence Evaluation III

This project was part of a larger effort to determine impacts of Ceratanova shasta on wild spring Chinook salmon in the Deschutes River Subbasin. Results from a pilot-level study conducted by USFWS and OSU Microbiology Department in 2016 found high levels of C. shasta spores in water samples collected in the Deschutes River, particularly at the mouth of the Deschutes River during the period when adults return and smolts outmigrate. A more in-depth study to document C. shasta spore densities and to genotype C. shasta present in the Deschutes River was funded by PCSRF in 2015 (15-Warm-04) and 2016 (16-Warm-05). These results will soon become available, which will direct future research. Given declining trends in spring Chinook escapement past the Warm Springs National Fish Hatchery and high fish to redd ratios documented since 2010 (average of 13.1 fish/redd 2010 – 2016 compared to 4.0 1977 – 2009), suggesting pre-spawn mortality, understanding when, where and what densities C. shasta spores are present in the Deschutes River and its tributaries where spawning and rearing occurs is of importance. Deschutes River spring Chinook spawn almost exclusively in Warm Springs River. In 2017, water samples in Warm Springs River and Shitike Creek, another tributary of the Deschutes River where spring Chinook spawn, were collected, filtered and stored for later analysis of C. shasta spore densities and genotyping under BPA Project 2008-311-00 - Natural Production Management and Monitoring. In addition, dead spring Chinook juveniles, caught in rotary screw traps, and adults, recovered during spawning surveys or a radio telemetry study, from Warm Springs River were frozen for histological analysis to confirm the presence of C. shasta or other pathogens that may have cause death.

The objective of this project was to quantify and genotype Ceratonova shasta spores in water samples collected in 2017 in two tributaries of the Deschutes River: Warm Springs River and Shitike Creek. Results in the tributaries, primary adult holding and spawning habitat for Deschutes River spring Chinook, will contribute to understanding spatial extent of C. Shasta in the lower Deschutes River. Samples from Warm Springs River and Shitike Creek that were collected in 2017 were to be analyzed under this project. However, OSU Dept. Microbiology was more efficient than expected and analyzed these water samples under project 15-Warm-04. They Found low densities of C. shasta spores from water samples in Warm Springs River in 2017, which indicated that spring Chinook were becoming infected in the Deschutes River. Water samples collected in Warm Springs River and Shitike Creek in 2018 will be analyzed under 16-Warm-05, in addition to longitudinal samples collected in the Deschutes River.

The savings from OSU Dept. Microbiology being able to process 2017 tributary samples as well as longitudinal samples collected in the Deschutes River in 2017 allows other related work to be done under this project. When Dr. Hallett, finishes analyses of 2018 samples (16-Warm-05), she will suggest how to modify objectives for this project. The modified project objective was changed to quantify and genotype Ceratonova shasta spores in water samples collected in 2019 in the Deschutes River.

By understanding the relationships between the parasite, its hosts, and the natural habitats and conditions that are favorable or unfavorable for infection, strategies can be developed to limit the exposure of fish to areas where the risk of infection of C. shasta may be higher, or develop management strategies based upon predicted water and climate conditions to improve the survival and viability of wild and hatchery salmonids. In addition to the fish host, C. shasta infects a freshwater polychaete worm. Actinospores are released from the worm, and infect fish, on contact, in the water column. Neither horizontal (fish to fish), nor vertical (fish to egg) transmissions have been documented under laboratory conditions, suggesting that the worm host is necessary for completion of the life cycle.
Research indicates that the potential for infection is enhanced when water temperatures are high, water flow is low, or numbers of infectious C. shasta are relatively high in the water column. Infection rates appear to be higher in or below still water environments than riverine ones. C. shasta can infect salmonids in a variety of ways, both internally and externally, and its effects on individual fish may range from mildly debilitating to fatal. Salmonids may be infected by the parasite at any developmental stage and at multiple locations. The natural resistance to C. shasta varies among stocks of fish and may even vary among family groups. Riverine conditions (e.g. temperatures, flow, and dissolved oxygen) affect a fish’s ability to resist infection. The degree and severity of infection may be linked to how far and how long an organism has been outside optimal conditions.

Dr. Hallett has been in collaboration with another of our colleagues, Ken Lujan, microbiologist with the USFWS Lower Columbia River Fish Health Center, and Terry Schrader at Oregon Dept. of Fish and Wildlife (ODFW). They completed a two-year study that combined sentinel fish exposures and water sampling in the Deschutes and Willamette rivers in 2015 and 2016 (USFWS Lower Columbia River Fish Health Center and OSU Microbiology Dept, 2016). The proposed work for 17-Warm-04 will build on these existing studies and provide insight C. shasta spore densities and genotype in primary spawning tributaries of spring Chinook and directly inspect mortalities for pathogens. This information will be used in conjunction with the BPA study in Warm Springs River, to better understand C. shasta risk to spring Chinook in the Deschutes River and a primary spawning tributary, Warm Springs River.

The CTWSRO believes we have a problem with pre-spawn mortality in spring Chinook holding in the WSR canyon and may be related to infection of C. shasta in spring Chinook and high water temperatures during summer when adults are holding. Redd numbers are very low compared to WSNFH escapement of wild spring Chinook (e.g., 5.7 fish/redd pre-2010 to 18 fish per redd 2010-2016, Figure 3). It is likely that spring Chinook from WSR are becoming exposed to C. shasta in the Deschutes River as juveniles and/or adults, returning to WSR, holding in warm stream temperatures (Figure 4), dying prior to spawning from C. shasta and/or egg survival is reduced for females exposed to high stream temperatures (McCullough 1999). The PCSRF study in the Deschutes River, in conjunction with the BPA study in Warm Springs River will advance understanding of what developmental stage that spring Chinook are becoming infected with C. shasta, if at all, where and when are high densities of spores present, allow assessment of risk of virility by associating stream temperatures with habitat use by developmental stage, whether polychaetes are infected and therefore acting as intermediate hosts, and may lead to further risk of infection.