entrainment of fish of all ages in water-management structures. Factors contributing to the decline of coho salmon are thought to include earlier overexploitation by fishing as well as continuing degradation of tributary habitat and reduced access to spawning areas. The threatened coho salmon also may be affected by changes in hydrologic regime, substantial warming of the main stem and tributaries, and continuing introduction of large numbers of hatchery-reared coho, which are derived only partly from native stock.
The U.S. Bureau of Reclamation's (USBR) Klamath Basin Project (Klamath Project) is a system of main-stem and tributary dams and diversion structures that store and deliver water for agricultural water users in the Upper Klamath Basin under contract with the USBR. After the listing of suckers in 1988 and coho in 1997, the USBR was required to assess the potential impairment of these fishes in the Klamath River Basin by operations of the Klamath Project. In the assessments, which were completed in 2001, the USBR concluded that operations of the project would be harmful to the welfare of the listed species without specific constraints on water levels in the lakes to protect the endangered suckers and on flows in the Klamath River main stem to protect the threatened coho salmon.
After release of the USBR assessment on the endangered suckers (February 2001) and following procedures required by the ESA, the U.S. Fish and Wildlife Service (USFWS) in April 2001 issued a biological opinion based on an extensive analysis of the relevant literature and field data. The biological opinion states that the endangered suckers would be in jeopardy under USBR'S proposed Klamath Project operations. The USFWS proposed a reasonable and prudent alternative (RPA) for operation of the Klamath Project. The RPA requires screening of water-management structures to prevent entrainment of suckers, adequate dam passage facilities, habitat restoration, adaptive management of water quality, interagency coordination in the development plans for operating the Klamath Project during dry years, further studies of the sucker populations, and a schedule of lake levels higher than those recommended by the USBR in its assessment.
The National Marine Fisheries Service (NMFS), which assumes responsibility for the coho because it is anadromous, issued a biological opinion in April 2001 indicating that the operation of the Klamath Project as proposed by the USBR assessment of January 2001 would leave the coho population in jeopardy. The NMFS formulated an RPA incorporating reduced rates of change in flow (ramping rates) below main-stem dams to prevent stranding of coho, interagency coordination intended to optimize use of water for multiple purposes, and minimum flows in the Klamath River main stem higher than those proposed by USBR.