Establishing Baseline Information on the Geographic Distribution of Fish Pathogens Endemic in Pacific Salmonids Prior to Dam Removal and Subsequent Recolonization by Anadromous Fish in the Elwha River, Washington

Abstract

Abstract After the removal of two dams, wild, natural, and hatchery produced fish are expected to recolonize historic habitats in the Elwha River. Fish populations previously isolated by the dams will interact, and potentially transmit pathogens. Geomorphic changes caused by dam removal could disrupt the balance between host and pathogen, resulting in pathogen transmission and amplification, potentially leading to disease. We reviewed historic stocking records and conducted an initial survey to better understand the distribution of salmonid pathogens in the Elwha River before dam removal. Review of hatchery plantings revealed that seven salmonid species were released throughout the Elwha River Basin since 1914. Approximately 61 million Chinook salmon (Oncorhynchus tshawytscha) and 40 million chum salmon (O. keta), coho salmon (O. kisutch), and steelhead trout (O. mykiss) were released below Elwha Dam from various stock origins. Additionally, 19 million salmonids were planted above Elwha Dam beginning in 1...