Watershed Restoration and Salmon Recovery in Knowles Creek
For over 15 years, Pacific Rivers Council's stream restoration project on Knowles Creek in Oregon's coast range has delivered scientific backing for our successful approach to salmon recovery.
Knowles Creek is a tributary of Oregon's Siuslaw River, joining it just a few miles from the ocean, with no dams or other major obstacles to prevent free-ranging salmon, trout and steelhead from completing their natural life cycles. Historically, this river system as a whole was probably the most productive coho salmon stream on the West Coast, and Knowles Creek hosts runs of coho (silver) and Chinook (king) salmon, steelhead, and sea-run cutthroat trout. The basin is almost entirely timberland, and has been extensively logged with the exception of a semi-protected old growth patch covering about 18% of the land area and a corresponding portion of the stream network.
Knowles Creek and its fish populations have been under continuous study for more than 25 years, with PRC taking the lead in 1991. Other partners in the studies include the Forest Service, Oregon State University, Oregon Department of Fish & Wildlife, Hancock Timber Company and more recently Ecotrust and the Siuslaw Watershed Council. Chief researcher is Dr. T. Charles Dewberry, working under a long-term contract with the Pacific Rivers Council. The combined efforts of conservation and restoration in the basin have earned the players the Austrian Thiessen Prize as the best watershed restoration effort in the world.
The most significant and important aspects of the studies are full-basin snorkel counts of the juvenile fishes, done every year by Dr. Dewberry since 1992, and annual smolt trap counts of outgoing salmon. We now know the number and location of all the fish in Knowles Creek to a reasonable degree of accuracy for the last 15 years, as well as the number of salmon heading to the ocean. This comprehensive and consistent data collection allows for inter-year and intra-year analysis of what kind of habitat in which reaches of the stream and its tributaries are the most and least productive under varying conditions. The results are telling.
During the study period so far, Knowles Creek has experienced its worst flood on record (Nov 1996-Jan 1997) and its worst droughts on record (1993), and during these period of substantial environmental stress, significant fish populations were able to persist only in the protected habitat. These reaches of higher quality habitat harbored all of the surviving fish, while the degraded habitat downstream, including sites that were undergoing or had undergone restoration, produced literally zero during these stressful periods. Even during normal years, approximately 20% of the habitat produced 80% of the fish. In sum, lose the best habitat and you risk losing it all, which may account for the well-known pattern of stream-by-stream extinction.
This striking finding leads to a conservation imperative: protection of the nodes of best remaining habitat is absolutely the first priority of any conservation and restoration plan. Restoration initiatives that are not preceded by protection of the highest quality habitats may be doomed to failure because marginal recovery of degraded habitats will essentially be for naught if the better habitats are simultaneously allowed to degrade. Furthermore, our research confirms that the salmon's freshwater life stages are as important as its ocean stages, despite the commonly held belief that ocean conditions are the primary factor affecting salmon populations.
The work at Knowles has provided hands-on opportunities for conservationists, policy-makers and landowners to learn proven stream restoration techniques. Tours of Knowles Creek with Charley Dewberry are eye-opening and intellectually challenging, particularly to those with some experience in river and freshwater habitat restoration. Salmon restoration will continue to be a critical area of study for years to come, and many people would benefit from this type of resource. PRC's salmon recovery strategy, with Knowles Creek as the showpiece, has the ingredients to improve stream restoration throughout the country.