Abstract
SummarySubstantial declines of Pacific salmon populations have occurred over the past several decades related to large‐scale anthropogenic and climatic changes in freshwater and marine environments. In the Columbia River Basin, migrating juvenile salmonids may pass as many as eight large‐scale hydropower projects before reaching the ocean; however, the cumulative effects of multiple dam passages are largely unknown. Using acoustic transmitters and an extensive system of hydrophone arrays in the Lower Columbia River, we calculated the survival of yearling Chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) passing one, two, or three dams. We applied a unique index of biological characteristics and environmental exposures, experienced by each fish individually as it migrated downstream, in order to examine which factors most influence salmonid survival. High outflow volumes led to involuntary spill in 2011 and created an environment of supersaturated dissolved gas concentrations. In this environment, migrating smolt survival was strongly influenced by barometric pressure, fish velocity, and water temperature. The effect of these variables on survival was compounded by multiple dam passages compared to fish passing a single dam. Despite spatial isolation between dams in the Lower Columbia River hydrosystem, migrating smolt appear to experience cumulative effects akin to a press disturbance. In general, Chinook salmon and steelhead respond similarly in terms of survival rates and responses to altered environmental conditions. Management actions that limit dissolved gas concentrations in years of high flow will benefit migrating salmonids at this life stage.
Highlights
Anthropogenic alterations within and adjacent to freshwater ecosystems have caused habitat degradation and loss, resulting in the decline of many aquatic species (Poff et al 1997; Dudgeon et al 2006)
Ecology and Evolution published by John Wiley & Sons Ltd
There was a significant difference between the survival of yearling Chinook salmon passing one, two, and three dams after controlling for release date
Summary
Anthropogenic alterations within and adjacent to freshwater ecosystems have caused habitat degradation and loss, resulting in the decline of many aquatic species (Poff et al 1997; Dudgeon et al 2006). The Columbia River Basin in western North America is one of the most dammed river systems globally and has experienced extensive anthropogenic alterations that have affected many organisms, including the early life stages of salmonids (Gresh et al 2000; Smith et al 2003). The creation of the Federal Columbia River Power System (hydroelectric dams and reservoirs) has significantly altered the physical, chemical, and biological structure of the Columbia River, including increases in water temperature, total dissolved gas, and predation pressure; altered flow regimes; and disrupted salmonid migration (Raymond 1979; Giorgi et al 1997; Bickford and Skalski 2000; Petersen 2001; Smith et al 2003; Kuehne and Olden 2012).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
