Cooperative Fish and Wildlife Research Units Program: Idaho
Education, Research and Technical Assistance for Managing Our Natural Resources

Lake Pend Oreille is a natural oligotrophic lake located in the northern panhandle of Idaho. It is the largest and deepest lake in Idaho and provides important recreational fisheries for a variety of salmonids, particularly kokanee, rainbow trout, and westslope cutthroat trout. In addition to providing an important sport fishery, kokanee are the primary prey species for threatened bull trout and large rainbow trout. Although kokanee harvest has been extremely high in the past (exceeding 1 million fish in the 1950s and early 1960s), their population has experienced a dramatic decline over the last 40 years. The exact mechanisms are unknown, but several factors have likely contributed to the decline of kokanee in the system. Some of these factors include barriers to movement (particularly during spawning), overexploitation, and changes to food web structure and prey availability resulting from the introduction of opossum shrimp. While these factors have undoubtedly had a negative influence on kokanee populations, the leading hypothesis for the decline and continued low density of kokanee in Lake Pend Oreille has been focused on water level management resulting from the construction of Albeni Falls Dam in 1952 on the Pend Oreille River. Albeni Falls Dam is used to generate power; consequently, operation of Albeni Falls Dam has had a major influence on water levels in Lake Pend Oreille. After construction of Albeni Falls Dam, the lake was maintained at high, stable levels throughout summer. Stable water levels are thought to have reduced the quantity and quality of suitable substrates for spawning. The objectives of this project are twofold. The first objective is to describe the spawning ecology of kokanee in Lake Pend Oreille. The second objective is to experimentally determine egg-to-fry survival associated with different substrate characteristics as it relates to water level management practices in Lake Pend Oreille.