Effects of Riprap Bank Reinforcement on Juvenile Salmonids in Four Western Washington Streams

Summer and fall juvenile salmonid populations in five pairs of stream sections were estimated shortly before and after construction of flood and erosion control projects. All five projects included bank reinforcement with rock riprap and three included streambed alterations. Juvenile coho salmon Oncorhynchus kisutch, juvenile steelhead Salmo gairdneri, and cutthroat trout Salmo clarki were apparently adversely affected by construction in the three smaller, and most severely altered, stream sections. Numbers of juvenile coho salmon and young-of-the-year trout were reduced somewhat, but those of yearling steelhead and cutthroat trout apparently increased, in the two newly riprapped sections of larger streams. Negative short-term effects of construction appeared to increase with severity of habitat alteration, to decrease with increase in stream size, and to decrease with increasing fish size.