Umatilla sub-basin assessment

Michael R. Maudlin

The Umatilla Sub-basin lies in north central Oregon State and is a tributary of the Columbia River. The Umatilla River and its major tributaries are home to a variety of salmonid species, including steelhead, bull trout, mountain whitefish, interior redband trout and three species of salmon. Changes in land and water use in the Umatilla Sub-basin have imperiled many of these stocks and driven all three salmon stocks extinct. The need for a screening process to rapidly characterize the sub-basin in terms of fish recovery is driven by the rapid decline of the remaining stocks and the poor returns of hatchery released salmon. The purpose of the Umatilla Sub-basin Assessment is to document the condition of the aquatic ecosystem of the watershed and establish the context for planning, monitoring and evaluation of restoration activities in the watershed. The goals are to gain an understanding of the aquatic ecosystem relative to the historic conditions, determine current risks to the aquatic ecosystem and identify conservation and restoration priority areas. The screening approach consists of three phases: a brief environmental history, a characterization the life history patterns and requirements for a group of key salmonids and a primary limiting factor characterization. Selection criteria for the key species consisted of a variety of economic, ecological and political concerns, including natural reproducing populations; the sensitivity of the species to similar aquatic conditions; and the amount of data available for the species. The limiting factor characterization followed from the life stage requirements for these species and focused on temperature and flow limitations in the seasonal use areas and migratory corridors. Based on the assessment it was possible to stratify the sub-basin into areas of biological importance based on key species distribution, life stage requirements and diversity. Determining the primary limiting factors to the life stages was more difficult because many of the potential limiting factors do not have threshold values associated with them. The limiting factor characterization did yield insight into flow and temperature limitations, but did not present a complete picture of the limitations these species face.

Umatilla sub-basin assessment

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