Survey of Pathogens in Hatchery Chinook Salmon with Different Out-Migration Histories through the Snake and Columbia Rivers

Abstract

The operation of the Federal Columbia River Power System (FCRPS) has negatively affected threatened and endangered salmonid populations in the Pacific Northwest. Barging Snake River spring Chinook salmon Oncorhynchus tshawytscha through the FCRPS is one effort to mitigate the effect of the hydrosystem on juvenile salmon out-migration. However, little is known about the occurrence and transmission of infectious agents in barged juvenile salmon relative to juvenile salmon that remain in-river to navigate to the ocean. We conducted a survey of hatchery-reared spring Chinook salmon at various points along their out-migration path as they left their natal hatcheries and either migrated in-river or were barged through the FCRPS. Salmon kidneys were screened by polymerase chain reaction for nine pathogens and one family of water molds. Eight pathogens were detected; the most prevalent were Renibacterium salmoninarum and infectious hematopoietic necrosis virus. Species in the family Saprolegniaceae were also commonly detected. Pathogen prevalence was significantly greater in fish that were barged through the FCRPS than in fish left to out-migrate in-river. These results suggest that the transmission of infectious agents to susceptible juvenile salmon occurs during the barging process. Therefore, management activities that reduce pathogen exposure during barging may increase the survival of juvenile Chinook salmon after they are released.

Received May 27, 2010; accepted January 17, 2011

ACKNOWLEDGMENTS

Funding for this study was provided, in part, by the Anadromous Fish Evaluation Program of the U.S. Army Corps of Engineers and the NOAA National Marine Fisheries Service. Project oversight and facility assistance was provided by the U.S. Army Corps of Engineers Walla Walla District office. Hatchery juvenile Chinook salmon were provided by Idaho Department of Fish and Game and the U.S. Department of Fish and Wildlife. We thank the Fish Passage Center for allowing us access to 34,000 PIT-tagged fish. Programming of the PIT tag sort-by-code functions was provided by Pacific States Marine Fisheries Commission. We thank Dina Spangenberg at NOAA Fisheries Service and Mary Bhuthimethee, Jerry Pruiett, Collin Christianson, Ben Campbell, and Bill Fleenor at University of California Davis for their assistance in fish collection, transport, and care. We thankfully acknowledge Lyndal Johnson and Mark Meyers for their critical review of this manuscript.