Report from the Beaver Patrol

Remember the story out of Juneau about a beaver patrol protecting Dredge creek and worrying because the beaver dams were ripped out? Well, it turns out a member of that patrol (Patricia O’brien) is a friend of the beaver management group on facebook and she sent us this:

Background

Dredge Creek runs through a U.S. Forest Service recreation area adjacent to a residential neighborhood. The creek heads near the Mendenhall Glacier Visitors’ Center. From its headwaters to Dredge Lake is only about one mile. Downstream from Dredge Lake it runs only about a third of a mile before emptying into a small holding pond before joining the Mendenhall River. Dredge Creek features coho salmon, Dolly Varden char, and cutthroat trout.

Beaver dams exist throughout Dredge Creek’s length. However, those dams have the potential for flooding trails. Below Dredge Lake, major trails are near the creek and the elevation of the trails is only slightly higherthan the creek. This area is heavily used by hikers, and dog walkers. Above Dredge Lake much of the terrain is rugged, and the area sees fewer hikers.

For about five years the U.S. Forest Service has agreed to allow a volunteer group (the Beaver Patrol) to work inthe recreation area. Additionally, a Boy Scout Weblos troop works with the Beaver Patrol, and the troop does most of the work in the creek above Dredge Lake. Except for months when ice limits beaver activity, the Beaver Patrol works in the area twice each week, and sometimes more. A goal of this partnership is to manage water levels to minimize trail flooding, while maintaining much of the habitat provided by the beavers. The Beaver Patrol has built; and maintained devices; to control water levels, even if beavers continue to add material to their dams. Where fish migration is encouraged, those devices are designed to allow fish to pass.

Excellent resource from Chuck! Thanks for putting this together. Every part of this is worth reading, but I especially liked this.

Obstructions to Migration

The first reaction for many viewing salmon in a stream with beavers is that the dams must be blocking salmon migration. Yet salmon have spawned upstream from several beaver dams in many watersheds for thousands of years. Often salmon may be seen mingling below a beaver dam until after a rain raises a stream’s level. One article commented that coho had no problem getting past beaver dams that were as high as two meters.Other articles observed no problems with coho getting past beaver dams. Steep steam banks allow beavers to build a much higher dam. Intuitively, it seems shallow water immediately downstream would make it more difficult for coho to jump over a beaver dam. Deeper water below an obstruction should enable coho to more easily jump over it. The higher the obstruction the deeper the takeoff pool should be. While the studies reviewed for this article did not cover this topic, the Beaver Patrol routinely clears material that would reduce the depth of areas below obstructions in Dredge Creek.

And what are their conclusions about beavers and salmon?

Conclusions

Pools created by beaver dams provide tailout areas preferred by coho for spawning. Since the Beaver Patrolclears impediments to fish passage twice each week when Dredge Creek in not frozen, it is unlikely that

spawning habitat will be a limiting factor to coho populations in Dredge Creek unless:

-people destroy redds after coho spawn

– construction causes sediment cover or otherwise degrade potential spawning habitat, or

– pollution degrades water quality.

Beaver ponds add summer coho rearing habitat in Dredge Creek. At least as important, by increasing water temperature and slowing stream velocity, beaver dams improve the winter survival of coho salmon in DredgeCreek.

Oh yeah, I guess that crazy researcher from the rogue agency NOAA has been right for all these years.