|Abstract or Summary
- A plan for the reestablishment of anadromous salmonid stocks into waters above the Pelton Round Butte Hydroelectric Project (PRB) located on the Deschutes River, Oregon has been under development since 1996. The PRB complex, starting at river kilometer (Rkm) 103, blocks the further upstream migration of anadromous salmonids into upper river basin waters. Part of the process for evaluating the passage plan was the development of a Fish Health Management Program. The program is, in part, designed to minimize and communicate the magnitude of risk associated with passing serious fish pathogens upstream of the PRB until evaluation of the fish passage effort confirms that the reestablishment of anadromous fish species can be successful. With the goal of minimizing the risk of passing serious fish pathogens along with evaluating the magnitude of risk, several potential pathogens of concern were identified. At the forefront of concern is the fish pathogen Myxobolus cerebralis which is responsible for whirling disease in salmonids. Annual, or at least periodic, introduction of M. cerebralis into the lower DRB has occurred since at least 1984 as a result of infected stray adult salmonids spawning and dying there. These are primarily hatchery summer steelhead (Oncorhynchus mykiss), and to a lesser extent spring Chinook salmon (O. tshawytscha), from the Snake River system.
Because of its' potential to cause significant mortality, the risk associated with M. cerebralis establishment in the DRB needed to be addressed. The risk of the parasite
being transmitted and established upstream of the PRB with the renewal of fish passage at the PRB, and the potential for M. cerebralis to affect survival of reintroduced anadromous fish species required investigation. To evaluate these potential risks, we conducted multi-year studies (1998-2007) that informed a risk-assessment model. Tailored specifically for M. cerebralis, this model was used to identify key characteristics that will influence pathways of M. cerebralis introduction, the potential for establishment, and the consequences of establishment. The three steps involved in the risk assessment model are the release, exposure and consequence assessments. Using this model we evaluated the probability of introduction and establishment of M. cerebralis in the lower Deschutes River Basin (DRB) as well as in waters above the PRB with future passage of anadromous fish.
The current study gives evidence that M. cerebralis is established in the lower DRB. The current study also gives evidence not all areas of the DRB can be classified as having the same likelihood for establishment and the potential impact the parasite poses will not be identical from one location to another. It is clear, however, that M. cerebralis could become established above the PRB if infected fish carry the myxospore into these waters.