INCREASING STREAMFLOW TO SUSTAIN SALMON AND OTHER NATIVE FISH IN THE PACIFIC NORTHWEST

I. INTRODUCTION To restore and protect the populations of wild salmon and other native fish in the Pacific Northwest--including measures called for under the Endangered Species Act-it is widely recognized by biologists and policy makers alike that significant changes will be required throughout the region. In the case of salmon, the seven native species in the northwestern United States have disappeared from about 40% of their historic breeding ranges during this century (National Academy of Sciences, 1996), and the size of the remaining wild stocks has been severely reduced. According to Nehlsen et al. (1991), 214 stocks are at high to moderate risk of extinction. In addition, annual returns of salmon to the Columbia River basin have decreased from an estimated 12-16 million fish before the 1930s to 2.5 million fish in the 1980s, including those produced in hatcheries. Although catch rates in some commercial fisheries have not declined significantly, most runs that appear plentiful today are composed largely of fish produced in hatcheries. Depletion of native salmon has led to extended restrictions and outright bans on recreational and commercial fishing for several species, and several stocks of salmon have been designated as endangered or threatened under the provisions of the federal Endangered Species Act, as have freshwater fish, including shortnose suckers (Chasmistes brevirostris) and Lost River suckers (Deltistes luxatus) in Upper Klamath Lake. The decline of salmon and native freshwater fish in the Pacific Northwest has resulted from numerous interacting activities, such as agriculture, forestry, grazing, industrial activities, urbanization, dams, interactions between wild and hatchery species, and fishing. Salmon are particularly vulnerable to this wide range of human influences because of their anadromous life cycle, whereby they spawn in fresh water, migrate to the sea, and return to their natal streams several years later to reproduce and subsequently die. For example, the hundreds of small and large dams that have been built on rivers throughout the Pacific Northwest have greatly reduced wild runs due to their effects on migration, the quantity and timing of water flows, velocity, water chemistry, and water temperatures (National Academy of Sciences, 1996). A range of efforts to reverse the decline in the populations of salmon and other native fish are being taken (or considered) at local, state, and federal levels. These efforts include tightening of harvest restrictions, modifications of dams and dam operations, and changes in the role of hatcheries in fishery management. They also include actions to protect the freshwater habitats of salmon and other native fish, such as riparian habitat protection and restoration and streamflow augmentation (see National Academy of Sciences, 1996). Streamflow is a key factor affecting the quality of salmon's freshwater habitat. Although the benefits to salmon for a specific increase in streamflows are difficult to assess precisely, biologists point to substantial scientific evidence that reductions in flows have contributed to the decline in salmon stocks throughout the region. Thus, a critical issue in the current policy setting will be how to maintain adequate streamflows to protect existing freshwater habitats and restore those that have been degraded. Interventions aimed at increasing streamflow to protect fish represent a new challenge to policy makers and resource managers, one for which little comparative or historical evidence exists as a basis for judging the costs or likely effectiveness of alternative approaches. Two distinct kinds of actions are at issue, one involving large-scale mainstem augmentation on the Snake and Columbia Rivers, the other involving much smaller tributary augmentation projects throughout the region. Because agriculture is the principal source of surface water diversions, accounting for about 80% of the total for the region, any efforts to augment streamflow will necessarily concentrate on reducing irrigation withdrawals--whether from thousands of upstream water users in the case of large-scale augmentation or from a handful of water users in a small basin. …