French Creek Slough Fish Passage Monitoring

French Creek enters the Snohomish River from the north near the town of Snohomish, Washington.  The watershed drains approximately 28 square miles, and consists of over 117 miles of stream and floodplain channels.  The downstream portions of the watershed have been significantly altered to support several dairy farms and other agricultural practices, and now consist of an extensive network of ditches, dikes and levees, and a complex pump/tide gate facility where the creek joins the Snohomish.  The pump station is screened to protect fish and has a fish ladder to provide upstream adult salmon passage during parts of the year.  Despite these efforts, the pump station still restricts adult migration and blocks juvenile salmonid access to French Creek. 

French Slough Flood Control (FSFC) operates and manages the pump station and associated fish passage facility.  In early 2005 FSFC contracted Wild Fish Conservancy (WFC) to design, build, install, and test a fish passage monitoring device at the pump station to determine the number, species, and timing of upstream fish migrants passing through their facility.  This information will help determine when the fish–passage facility (which requires substantial amounts of electricity), must be operational.

WFC designed and built a motion-activated digital video recorder to capture images of every fish that passes through the FSFC fish passage facility.  The equipment records a short video of each fish that jumps over a weir in the fish passage facility. The images allow investigators to document the species of fish and determine whether it is wild or hatchery origin by the presence or absence of an adipose fin.  At night, the cameras automatically switch to infrared lighting to minimize the risk of affecting fish behavior.  Each fish image is automatically marked with the date and time of passage.

The video surveillance of fish passage at French Slough began on October 6, and within the first month, over one hundred coho salmon have been documented passing upstream through the FSFC facility. Over the full study period, a total of 503 adult coho salmon (Oncorhynchus kisutch) were documented passing upstream above the false weir at the French Slough Flood Control facility. Because blackouts occurred during the first month of monitoring, it is likely that over 600 adult coho actually entered the French Creek watershed during this study time period. Of the 503 coho salmon documented, adipose fin presence/absence was determined for 62%. In these cases, only 3% of the coho were ad-clipped; 97% had an intact adipose fin. While no other fish species were documented during the first season of monitoring, two mink (Mustela vison) and one muskrat (Ondatra zibethicus), were observed to pass through the fish passage facility.