Welcome to our Fish Factors Mini-Series! Each quarter we will share important stories on factors impacting Upper Columbia salmon and trout!
*Written by Tracy Bowerman
Salmon and steelhead have complex life cycles and over the course of their lives, an individual will occupy many different habitats. Each habitat must meet certain conditions in order for salmon to survive that life stage. In the previous “Fish Factor,” we examined some of the evolutionary characteristics salmon have developed in order to survive long, homeward migrations to their birth locations. In this “Fish Focus,” we explore the adaptations and challenges of the pre-spawn life stage, the time after salmon have arrived at their natal streams but prior to reproducing.
Once Pacific salmon have completed their homeward migration to spawning grounds, many species wait for a period of weeks to months for water temperatures to cool before they commence spawning in the fall. Sockeye salmon typically spend this waiting period in lakes, whereas spring Chinook salmon seek cover from predators in deep pools and under logs and undercut banks in streams near their spawning areas. Salmon do not feed during this holding period, relying entirely on stored energy accumulated in the ocean.
During this holding period, salmon are at risk of predation and susceptible to stress from high water temperatures and other water quality impairments. Recurrent die-offs of adult coho salmon in the Seattle area have been linked to chemicals found in automobile tires that get deposited onto roadways and subsequently drain into streams during storm runoff events. In other areas, sockeye and spring Chinook salmon pre-spawn mortality has been associated with high water temperatures, which may increase stress and susceptibility to pathogens, or even lead to direct mortality if temperatures get too high. . Thus, cold, clean water is imperative for adult salmon during this critical period between migration and spawning. Actions that can help ensure favorable conditions include maintaining healthy riparian conditions to provide shade, filtering urban runoff, and improving connectivity between streams and adjacent floodplains to reduce stream warming.
See additional pre-spawn mortality data.
Photo: Tiffani Linbo, NOAA fisheries