June 2000
Chief Scientist: Jim Scott
Contact: Dave Seiler (360) 902-2784

With some 73,000 boats passing annually between Puget Sound and the fresh waters of Lake Washington, the Hiram M. Chittenden Locks near Ballard in Seattle is the busiest facility of its kind in the country.

Sharing the water with those commercial and pleasure craft are millions of migrating fish– young chinook, coho and sockeye salmon and steelhead. Depending on weather conditions and other factors, each year as many as four million sockeye salmon, 100,000 wild chinook, 100,000 wild coho and three million hatchery-produced chinook and coho make their way from rivers and streams feeding Lake Washington on their way to the ocean.

Designed to provide boat passage and regulate lake water levels between sea-level Puget Sound and higher-elevation fresh waters, fish passage was not a major consideration when the locks were constructed nearly 90 years ago. Only in recent years has attention turned to the toll this man-made marvel takes on fish.

Salmon and steelhead already face an array of challenges in the Lake Washington system, the state's most heavily urbanized watershed. Besides habitat loss and degraded stream conditions, the lake is populated with introduced and native predators such as bass and cutthroat trout. The locks present a final gauntlet– and sometimes a fatal one– for fish making their way to sea.

In the last decade, scientists with the Washington Department of Fish and Wildlife (WDFW) have raised concerns about the plight of smolts (young salmon and steelhead) passing through the locks. In 1994, WDFW scientists began evaluating smolt survival at the locks and found that hundreds of fish were dying with each lockage (the term for each time the lock chambers are filled with water to allow boats to pass between the Sound and fresh water).

The fish were battered as they passed through barnacle-encrusted pipes at the bottom of the lock chambers at high speeds while the lock chambers were being filled. For young fish facing the stress of adjusting from freshwater to a saltwater environment, those injuries were fatal.

Concerns about salmon smolt survival took on fresh urgency with recent federal endangered-species protection listings for Puget Sound chinook.

Once the problem was recognized, a multi-agency task force was formed in the mid-‘90s to improve smolt survival at the locks. Besides WDFW and the Muckleshoot Tribe, co-managers of fish in the Lake Washington system, the task force included representatives of the U.S. Army Corps of Engineers which operates the locks, the National Marine Fisheries Service and, more recently, salmon recovery officials from King County and the City of Seattle.

The scientific task force recommended changes in both operations and facilities to make the locks more fish friendly, and then assessed the effectiveness of the changes. The improvements included slowing the rate at which the large lock chamber is filled with water, from about four minutes to as much as 20 minutes per fill. In addition, in 1995 a prototype smolt passage flume was placed atop the dam adjacent to the lock chamber, to provide fish with a safer, alternate passage route. This year that prototype flume was replaced with four new smolt slides. The open-top steel flumes allow fish to follow water flow and glide unharmed past the locks.

To measure the effectiveness of the slower fill rates and passage improvements, several monitoring operations are underway:

• WDFW and Muckleshoot fish biologists and technicians spent 20 days this spring using a purse seine net to collect and count the number of young fish which wind up in the lock chambers. Earlier seining studies, beginning in 1995, indicated that the prototype slide effectively passed a large proportion of smolts.

• About 10,000 hatchery-produced chinook smolts and 3,000 of their wild counterparts this year were implanted with tiny electronic passive integrated transponder (PIT) tags, which can be detected by electronic readers mounted on each of the flumes. Besides increasing scientists' understanding of how fish navigate the locks, and how effective the smolt flumes are in passing fish, the PIT tags provide scientists with vital information for separate predation studies by indicating the various survival rates of fish tagged and released at different distances from the locks. The tiny PIT tag capsules, each a half-inch long by less than an eighth-inch in diameter, contain an integrated microchip and antenna coil. The PIT tags are implanted with a hypodermic needle into the fish's coelomic cavity in which its digestive organs rest. When a PIT-tagged fish passes the electronic readers, a signal emitted from the reader is picked up by the PIT tag, which returns an alpha-numeric response. Unlike mass marking methods, the PIT tags allow scientists to identify an individual fish and thus gather valuable information about migration patterns, growth and survival.

• WDFW scientists soon will install a metal-frame net pen below the flumes to collect smolts so biologists can assess their condition after passing through the slides. The pen consists of a net pen enclosed in an 8-by-20-foot metal frame with perforated aluminum floor and sides, extending eight feet into the water below the slides. Besides helping in the evaluation the fishes' condition after passing the flumes, the net pen collection box offers scientists a tool to determine the species composition of fish migrating past the locks.

With the locks' unique location as a "nozzle" between fresh and salt water, these evaluation tools have long-term applications for evaluating other salmon recovery efforts.

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