Influence of Waterway Development on Migrational Characteristics of Juvenile Salmonids in the Lower Willamette River, Oregon

Abstract

We investigated the effects of Portland Harbor development in the lower Willamette River on the migration and behavior of juvenile salmonids (Oncorhynchus spp.), the habitat occupied by juvenile salmonids, and predation on juvenile salmonids by northern squawfish Ptychocheilus oregonensis. Juvenile salmonids were abundant in the lower Willamette River during spring; radio-tagged juvenile steelhead O. mykiss and yearling chinook salmon O. tshawytscha usually migrated through the harbor in 1–3 d. We did not detect any spatial pattern in the downstream migration of radio-tagged fish or any difference in behavior of radio-tagged fish among the developments. Habitat used by juvenile salmonids at an undeveloped site was unavailable at developed sites, especially at a site with a vertical-wall shoreline. We caught more northern squawfish in areas without development, and we found no difference in the frequency of northern squawfish digestive tracts containing juvenile salmonids between developed and undeveloped areas. We concluded that waterway developments presented few risks to migrating juvenile salmonids. However, whenever possible, activities such as dredging and construction should be avoided in spring when juvenile salmonid abundance is high. The location of developments need not be weighted heavily when considering their effects on juvenile salmonids. Further research is needed to determine the effects on juvenile salmonids of altering bottom slopes, water depths, and water current velocities at developments. Predation by northern squawfish in Portland Harbor is not enhanced by development.