Investigation of Juvenile Salmon Distributions Among the Large Piers Along the Elliott Bay Seawall in Seattle, Washington

The City of Seattle is currently underway with the planning and designing of a replacement of the 7,000 foot long seawall supporting the downtown waterfront.  The seawall and associated urbanization of downtown Seattle have markedly altered the aquatic habitat conditions along the waterfront.  Specifically, the seawall was built waterward of the historic shoreline and nearly eliminates all shallow water habitats.  The seawall is also lined by a series of large historic piers which extend far out into the water and create large shaded areas where no direct sunlight reaches the water.  The waterfront is also located within five miles of two major river systems which support populations of salmon that outmigrate as juveniles and utilize the marine nearshore shorelines to different extents depending on species.   Chinook salmon are produced in both river systems and the Puget Sound populations are listed as threatened under the federal Endangered Species Act.  Chinook are also one of the two salmon species that most extensively use shoreline marine nearshore habitats after outmigrating from their natal rivers. Previous studies have shown that juvenile salmon migrating along the marine shoreline tend to avoid shaded areas when there is a sharp light-to-dark contrast.  This avoidance of shaded areas is documented to result in several hours of delay to the juvenile salmon’s migration.  These studies are based on fish observations around single large pier structures, but no studies have documented juvenile salmon movements and potential delays along a waterfront with a series of large overwater structures. In order to better inform the design of restoration elements being considered as part of the seawall replacement, the City of Seattle is conducting a fish study to investigate juvenile salmon distributions and movements along the seawall.  The study is using snorkel and land-based visual techniques to monitor juvenile salmon and other fishes near the seawall between February and September 2011.  This poster will present the preliminary findings of the investigation.