Responses of fish occurring in shallow subtidal and intertidal habitats to sediment changes resulting from removal of the Elwha River dams

Removal of two dams on the Elwha River, Washington, is expected to help restore natural sediment processes to the coastal environment near the river mouth. We are interested in assessing the responses of fish using shallow subtidal and intertidal habitats to the sediment changes resulting from this landmark event. Responses of fish in using these habitats are of particular interest because sediment changes will likely be especially significant in these habitats, ecologically important forage fish spawn and rear in intertidal areas, and juvenile salmon from federally protected populations use intertidal and subtidal habitats to migrate to ocean rearing areas. Since 2005, we have been collecting biotic data (e.g., species composition and size distribution) on the intertidal/subtidal fish community at sites near the Elwha River mouth and at more distant reference sites. We have used these initial findings in combination with the results of predictive sediment modeling to develop indicators of fish responses to this habitat restoration. Examples of bio-indicators include changes in the composition and sizes of benthic species (e.g., flatfish) with specific substrate requirements, changes in fish diversity, reproduction of intertidal and shallow subtidal species (such as surf smelt), changes in trophic food webs (by monitoring changes in predator/prey interactions and diets), and the prevalence of juvenile salmon that are migrating through this area. We hypothesize that responses of littoral zone fish will depend on when and how much sediment reaches the coastal environment; composition and distribution of the material once it reaches Puget Sound; and how long it takes material to distribute from the river mouth.