Recovering An Economically Viable Population of Coho Salmon in the Siuslaw River, Oregon.

Historically, the Siuslaw had arguably the largest run of coho salmon south of the Columbia River. Since the 1990's the run has been less than 5% of the historical abundance.  This presentation focuses primarily on basin restoration but touches on the broader aspects as well.

            The functional unit of the Siuslaw basin is the tributary stream basins because the mainstems of the Siuslaw and Lake Creek are too warm to rear salmonids during the summer.  In six out of ten years from 2000-2010, we snorkeled over 250 km of stream within the Siuslaw basin annually. In each tributary basin we examined the current abundance and distribution of coho salmon within the context of its long-term management history. In two out of three years there was a statistically significant difference between the abundance and distribution of coho salmon and the tributary basin's management history. We used the whole-basin snorkel count of Knowles Creek and the smolt trap information from 1992- present to examine some aspects of the population dynamics of juvenile coho salmon.

            We believe that the primary factor limiting coho production in the Siuslaw basin is debris flow deposits that create dam-break floods.  The resulting wall of water logs, rock and sediment not only destroys a large number of coho redds but it destroys habitat for decades.  These destructive events disrupt the natural flow of water, organic matter, and sediment.

            To recover economically viable populations one possible scenario is as follows: 1) first prioritize tributary basins that have minimal risks of dam-break floods. 2) implement practices that over time will decrease the risk of creating dam break floods. 3) focus on the headwaters in basins of less than 15 ha to build a core area of minimal risk to anchor the populations.  Then build downstream.