Research Briefs

Research
Investigate relationship between adult salmon freshwater migration and flow

Species concerned: Chum salmon.

Investigators: Steve Boessow, Terra Hegy, Hal Beecher, Bob Vadas, Alan Wald, Science Team, Habitat Program.

Purpose of research: Determine the role of flow on the timing and relative abundance of salmon entering a stream. Specifically, investigate whether rainfall events, and thus higher flows, are followed by increased numbers of adult salmon entering a freshwater system. Anecdotal evidence indicates that rainfall indeed does affect the movement of salmon into freshwater such that during drought years coho have been observed to stay in estuaries longer and delay entry into rivers. When managing water diversion and storage, it may be important to consider this function of flow.

Perry Creek in Thurston County was chosen as the site to test our assumptions because it is close enough to Olympia to make daily observations feasible, small enough to access multiple sections as index sites without missing much of the run, we had WDFW and WDOE data on flow and fish from the past 10 years, and we had excellent cooperation from adjacent land owners.

In September, prior to fall rains and before any adult fish movement, we installed a staff gage and took regular discharge measurements. We walked the entire length of the creek accessible to fish (about one mile). We chose two stream segments to count fish, then conducted weekly observations and discharge measurements until the first adult salmon appeared. Upon the first sighting of salmon we began daily fish counts and staff gage readings along with occasional discharge measurements.

The first chum were sighted on October 18, 2003. In early December we are still counting fish on a daily basis, and still have new fish entering the system. We have seen high flows damage our original staff gage, observed daily changes in distribution of large woody debris (LWD) and been overwhelmed by the volume of salmon spawning in and migrating through our study sites. It is expected that we will continue to make daily trips to Perry Creek until sometime in January 2004.

Geographic area: Perry Creek, Thurston County, Washington.

Timeframe of study: Fall 2003 through 2004 (at least).

Joint partners: None.

Funding: Funding is limited to position budgets for time worked. Water Team staff are coordinating the fish counting duties that are taking 1-2 hours per day during peak of spawning and 1 hour per week or less when fish are not present.

Are volunteers needed: No.