Historical changes in fish habitat for select river basins of eastern Oregon and Washington

From 1934 to 1942 the Bureau of Fisheries surveyed more than 8,000 km of streams in the Columbia River basin to determine the condition of fish habitat. Changes in fish habitat over time were evaluated by resurveying a subset of the historically surveyed streams in the Tucannon, Asotin, Grande Ronde, Yakima, Wenatchee, and Methow river basins from 1990 to 1992. Historical reviews show many streams as degraded from past land management practices (e.g., timber harvest, splash dams, stream channelization, livestock grazing, and mining) before the 1930s. Our basin resurveys show a decrease in large pools ( greater than or equal to 20-m super(2) area and greater than or equal to 0.9-m depth) in managed watersheds (multiple-use, p < .05), while large pools in unmanaged watersheds remained the same or increased (p < .05). Results for these six river basins suggest a regional pattern to this change. Large pools increased in the Mid-Columbia region (Yakima, Wenatchee, and Methow basins; p < .05) regardless of management history, with the increase being twice as great in unmanaged watersheds. In the Blue Mountain region (Tucannon, Asotin, and Grande Ronde basins), large pools decreased significantly (p < .05). The current frequency of coarse woody debris was significantly higher (p < .05) in unmanaged than in managed basins. Differences in land-use histories for the mid-Columbia and Blue Mountain regions partially explain current fish habitat conditions and the declines in anadromous fish runs. Strategies to protect, restore, and maintain anadromous and resident fish habitat need ecosystem approaches that protect as well as restore the remaining habitats.