Projects & Programs
Effects of Shoreline Hardening and Shoreline Protection Features on Fish Utilization and Behavior, Washaway Beach, Washington
Armor used for erosion control structures in Washington State waters has both physical and biological effects. Though the physical effects of shoreline armoring have been somewhat studied, the anticipated effects of habitat modification are poorly documented and poorly understood. To better understand the effects of various armoring strategies and to devise least damaging alternatives, it is critical to acquire a systematic data set on ecological impacts from these structures.
The objective of this study was to develop an understanding of whether groin-type structures on the outer coast can alter migratory movement or predation pressure on juvenile salmon. Jacobson's Jetty, the Washaway Beach dike and groin structure, is an example of such a feature and provides an opportunity to conduct coupled studies on the physics and biology of these structures in this environment.
Specifically, PNNL coastal scientists used this study to assess the differences in predator abundance and predation pressure between the armored site and nearby unstructured sites, the differences in juvenile salmon migratory behavior between the two sites and the physical conditions and processes that could contribute to differences in predation and migration between armored and unstructured sites. Scientists used precision split-beam echo sounders to locate and map fish, evaluated numerical model results and conducted field experiments for model verification, conducted diver surveys to observe and document fish abundance and behavior and used a variety of techniques to capture, identify and document the location abundance of nearshore species. This site was a particular challenge due to the extremely strong tidal currents–up to five knots–and the exposure to large Pacific Ocean waves.