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Subject:   Salmon Oust Unwanted Guests With "Beaver Deceiver"
For Immediate Release:   
7/27/2007  11:45:00 AM
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Salmon Oust Unwanted Guests With "Beaver Deceiver"
Device Lets Busy Beavers Build Dams Without Blocking Salmon Runs


SEATTLE - After Seattle City Light spent $300,000 to restore the Powerline spawning channel on the Skagit River to give salmon an off-river area to lay eggs, the habitat drew a few unwanted guests that were blocking access for thousands of fish: dam-building beavers.

But an experimental device called the “Beaver Deceiver” that is now being used by City Light in cooperation with the National Marine Fisheries Service (NMFS), a division of the National Oceanic & Atmospheric Administration (NOAA), is helping protect salmon runs without bothering the hard-working, flat-tailed rodents.

“The reason we’re building this is to provide off-channel habitat during periods when the river floods. Because we have our dams at the headwaters of the river, there isn’t the same frequency or magnitude of floods and the natural off-channeling doesn’t occur. The river isn’t capable of building this type of habitat, yet it’s essential for coho and chum production,” Seattle City Light Fish Biologist Dave Pflug said.

The beavers are a challenge because the dams they love to build cut off the salmon from the new spawning grounds. And tearing out beaver dams wouldn’t solve the problem for long.

“They can completely rebuild or build a new one overnight,” said Jason Hall, a federal research fish biologist with NMFS. “They build very sturdy dams that require up to eight hours to remove one dam.”

So rather than fight with the beavers, City Light and NOAA are experimenting with a NOAA-designed device that tricks beavers into thinking they have successfully dammed the small channel.

The Beaver Deceiver is a large box built with a culvert and fish ladder inside. It works by reducing the sound of flowing water and tricks the beavers. Running water will trigger beavers’ dam-building behavior. But now, with the “Deceiver” incorporated into the beavers’ dam, the device constricts water flow enough to allow a pond to form without cutting off the channel.

Salmon get a clear route to their spawning grounds in the fall. In the spring, the small fry are able to bypass the beaver dam by way of a fish ladder. Meanwhile, the beavers get the protection of their dam and increased habitat for their favorite food sources: willows, cottonwoods and lots of aquatic vegetation that grows in riparian areas. The fish are happy and the beavers are happy.

If this experiment continues its success, it could be a big benefit for agencies trying to rebuild natural habitat. In other parts of the country, agencies have spent up to $100,000 building permanent structures to get fish around beaver dams. The beaver deceiver costs about $500.

City Light operates three hydroelectric dams on the Skagit River that provide about 17 percent of the electricity used by the utility’s customers. The Skagit is the only river in Washington that supports all five species of salmon plus steelhead and bull trout. Three of the species are listed as endangered.

Still photos and video of the Beaver Deceiver are available. Arrangements can be made for on-site tours of the area. Contact City Light Strategic Advisor Scott Thomsen at (206) 615-0978.



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