Beaver benefits
Dear Editor:
Re: “Methow Okanogan Beaver Project concerned about dam damage” (Aug. 26).
Beaver dam analogies (BDAs) built by stream restoration projects, and beaver dams have coincidental benefits to both humans and wildlife. The stabilization of stream flow benefits the groundwater table that our wells depend on, surface water that supports much of our agriculture, and adjacent wetlands. These changes to stream structure also effect almost all wildlife at some stage of life and especially salmon, steelhead, and other fish species.
It is not unusual that beaver dams are assumed to be obstacles to fish migration and therefore detrimental to fish reproduction, but many decades of research has proven that streams with beaver altered habitat are much more productive habitats for salmon and steelhead. Although beaver dams can be barriers to fish migration, it is usually only for short time periods and the effects of beaver dams to filter and settle out fine sediments greatly improves the conditions that create the best quality spawning gravels below and between beaver dams. It is often these short stretches of fine sediments-free gravels, a small part of a stream system, that produce the greatest amount fish.
Although beaver ponds expose more water area to sunlight that may increase surface temperatures, this effect is offset by greater stream flow stability, thermal capacity, and thermal exchange with subsurface water. The deeper water areas of the ponds also provide fish refuge from extreme daily stream temperatures highs.
The trapping of North American beavers began in the 1600s. By 1900 beavers had been eliminated from almost all their former habitat from Mexico to the Arctic Circle. Biologists at this time were concerned by the degradation of watersheds across the North American continent as their stream and wetland structures unraveled in the absence of beavers. A moratorium on beaver trapping was declared nationwide. Within a few decades, beavers were expanding into much of their former ranges, but in many of the upper reaches of watersheds in the arid West, they have never re-stablished their presence.
Gary Ott
Twisp
