Tribes find ways to keep beavers from blocking fish passage

Beavers are tenacious animals whose mission in life is to stop the flow of water so they can create a pond for their lodges. Unfortunately, their dams often block fish passage.

Tribes have had to find creative ways to discourage beaver activity enough to let salmon access spawning habitat.

“Beaver deceivers” have become a popular and inexpensive way to deter the animals, but they aren’t effective in every situation. “We need to find site-specific alternatives,” said Jon-Paul Shannahan, fisheries biologist for the Upper Skagit Tribe.

Beaver dam building behavior is triggered by the sound of flowing water. A beaver deceiver is a box that constricts water flow in a stream just enough to allow a pond to form. Large pipes are enclosed inside the box to obscure the source of running water. Since the beavers can’t hear the flowing water and their pond needs are being met by the increased water level, they aren’t compelled to build a dam. A fish ladder inside the beaver deceiver enables adult salmon to pass upstream.

“Beaver deceivers only work when there is just one point of constriction where beavers like to build dams,” Shannahan said.

Working with the National Oceanic and Atmospheric Administration, the Upper Skagit Tribe installed a beaver deceiver in a bottleneck of a Skagit River channel in Rockport. “We haven’t had any beaver dam blockages in that channel since we installed the deceiver,” Shannahan said.

A beaver deceiver in a Skagit River channel in Rockport meets beaver dam needs and prevents the animals from blocking fish passage.

In other channels, Upper Skagit natural resources staff have had success keeping beavers out of culverts by fencing them with mesh big enough to allow adult fish passage, but too small for beavers. During a visit in mid-November, dozens of chum were seen upstream of the caged culverts.

In areas where fencing and beaver deceivers can’t be used, the tribe tries to discourage dam building by planting vegetation that beavers don’t like to eat, such as conifers, spruce and cedar.

Near the Port Gamble S’Klallam reservation, beavers blocked an undersized road culvert in Martha John Creek, preventing chum salmon from moving upstream into an open wetland.

“There’s no reason why this area shouldn’t be great habitat for salmon,” said Hans Daubenberger, the tribe’s habitat biologist. “We’d like to see the chum and coho from Port Gamble Bay make their way up here to spawn. Chum can get only to the culvert before they are stopped. This is the only part of the stream that hinders their progress.”

The tribe worked with Kitsap County and Great Peninsula Conservancy this fall to remove existing beaver dams and install cattle fencing to enclose the culvert’s upstream opening.

Cattle fencing surrounds the upstream end of a culvert on Martha John Creek to prevent beavers from constructing dams.

“We had signs of beaver activity and had to do some initial modifications after we installed it in September. But since mid-October, it was pretty quiet down here,” said Jessica Coyle, the tribe’s response program manager.

The enclosure establishes a considerable space between the fence line and the water running through the culvert, discouraging beavers from building dams along the fence. The culvert will be replaced with a larger one in a few years by the county, but the tribe didn’t want to wait to open the culvert for fish passage. Once the proper-sized culvert is installed, the beaver problem will disappear.

“The sooner we get it flowing, the better,” she said.

For information, contact:
Jon-Paul Shannahan, Upper Skagit Tribe, 360-854-7089 or [email protected]; Jessica Coyle, Port Gamble S’Klallam Tribe, 360-297-4792 or [email protected]; Kari Neumeyer, NWIFC, 360-424-8226 or [email protected]; Tiffany Royal, NWIFC, 360-297-6546 or [email protected].