A protocol for assessing the impacts of urbanization on coho salmon with application to Chester Creek, Anchorage, Alaska

Abstract

Coho salmon (Oncorhynchus kisutch) abundance has declined in many urban streams. The causes of these declines can be hard to identify because urban impacts on stream ecology are complex and can vary between watersheds. This makes it difficult to develop appropriate and effective strategies for stream rehabilitation or mitigation aimed at increasing coho productivity. To improve this situation I developed a habitat quality assessment protocol for urban coho salmon to help identify significant habitat degradation as a prelude to restoration planning. To evaluate the protocol I used it to assess coho habitat quality in Chester Creek, Anchorage, Alaska, an urban stream that once supported a large population of coho salmon but now only supports a remnant population. I compared habitat characteristics from one non-urban and two urban study reaches to 'healthy' standard guidelines. This application of the protocol showed that the most significant adverse effects of urbanization on coho salmon habitat in urbanized reaches were increased flood intensity, barriers to adult and juvenile migration, reduced physical habitat complexity, siltation of spawning gravels, stressful water quality conditions, and stocking of potential predators and competitors. These results provide useful information for prioritizing rehabilitation and mitigation efforts in Chester Creek.