Rivers of Resilience – Asotin Creek

In California, Idaho, Oregon, Science Friday, Steelhead Files, Washington by Nick Chambers

Asotin Creek is a tributary that drains into the Snake River near the town of Asotin in eastern Washington.  With a drainage area of 250 square miles, Asotin Creek is slightly larger than the Wind River, but also much smaller than the Yakima River watershed.  Like the Yakima, the basin is located in a semi-arid environment. Most of the watershed is privately owned and the main land use is cattle ranching.  As a consequence, over the past 100 years much of the creek channel has been straightened, channelized or moved.  Asotin Creek and its tributaries have benefitted from habitat restoration ranging from riparian improvements to additions of large wood. We have high quality data for the Asotin because it is in NOAA’s Intensively Monitored Watershed program, a region-wide effort that uses individual watersheds to evaluate the efficacy of habitat restoration projects with respect to wild salmonid abundance.




Asotin Creek is a Snake River tributary located above eight dams on the Columbia and Snake rivers.  The Asotin is particularly interesting to evaluate because it helps us gauge the potential of wild steelhead to flourish when they have to pass many dams and occupy habitat that has been highly degraded but is being restored.   Hatchery steelhead were released near the mouth of Asotin Creek for an extensive period until 1997, when the plants ceased.  Given that most of the interior Columbia hatchery fish return after spending only one year at sea, 1999 would be the first year of returning wild adults that did not compete with hatchery smolts or adults from the previous hatchery releases.


We can see from Figure 1 that annual run sizes of wild steelhead were significantly different in years when hatchery fish were released compared to when they were not.   Specifically, the wild population averaged only 387 steelhead per year from 1986-1998, the hatchery release time period, compared to an average of 667 wild steelhead per year post-hatchery.  That is almost 2x more fish on average.


As with the Wind and the Yakima, we do not have the data to parse out how much of the wild steelhead resurgence in the Asotin is due to cessation of hatchery releases versus other factors, including improved spill over the dams, changes in ocean conditions, and habitat restoration. This, again, highlights the need for more in depth experiments and monitoring projects that can identify the relative effects of each factor so that we can understand the factors most relevant to wild steelhead recovery.


What is clear is the fact that the Asotin’s wild steelhead are doing well in the absence of hatchery releases, and they indicate that wild steelhead can rebound despite having to pass eight dams and occupy habitat that has been extensively altered.  More wild steelhead have returned to the Asotin in the past five years than any other five year period over the previous thirty years. That bodes well, and highlights the potential that wild steelhead have even in some of the most distant inland streams.


Asotin Graph

Figure 1. Annual abundance of adult wild steelhead in Asotin Creek when the hatchery steelhead were being released and after the hatchery releases were ceased.