Distribution of Fish and Crayfish and Measurement of Available Habitat in the Tualatin Basin

Streams of the Tualatin River basin within the urban growth boundary near Portland, Oregon, have undergone substantial changes in water quality, fish habitat, and fish assemblages. Changes in landscape attributed to logging, agriculture, and urban development have affected the hydrology of the basin. Fish populations in the Tualatin River basin have never been quantitatively surveyed, and little has been done to study aquatic habitat; therefore, long- term effects of habitat changes on fish populations are poorly understood. 

The Oregon Department of Fish and Wildlife (ODFW) and the Unified Sewerage Agency (USA) are concerned about the influence of urban development on streams in the Tualatin River basin. Little is known about the current status of fish populations and aquatic habitat in the basin, how urbanization affects these fish populations, or about the possibility of fish populations benefitting from habitat enhancement. 

In 1993 ODFW and USA began a cooperative study to (1) describe the status and characteristics of fish populations in streams of the Tualatin River basin within the urban growth boundary, (2) describe the status of aquatic habitat in these streams, and (3) examine the relationship between fish assemblages and aquatic habitat to identify stream reaches that would most likely benefit from habitat enhancement. Also identified were streams where protection from habitat degradation should be of high priority, and streams where fish populations may not benefit from habitat enhancement because of water quality or other problems. 

We identified 38 reaches of 15 streams to be sampled. We surveyed fish populations in spring, summer, and autumn, 1994, and in winter 1995. We surveyed aquatic habitat in of the streams in late summer and early autumn 1993, and in the remaining 8 streams in late summer and early autumn 1994.