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Eight large Federal hydropower dams were constructed between the 1930's and 1970's on the mainstem lower Columbia and Snake Rivers, U.S.A. The dams included fishways that enabled effective upstream passage of adult salmonids to Snake River basin spawning areas, but they lacked any facilities for protection of juvenile salmonids migrating downstream to the ocean. Prior to completion of the dam complex, early studies on mortality of juvenile salmon passing through turbines suggested that Snake River salmon stocks could not survive the cumulative mortalities to populations of fish that would have to pass downstream through turbines at all eight dams. This led to a more than 30-yr field effort conducted primarily by NOAA's National Marine Fisheries Service personnel to devise, test, and recommend for installation effective screening systems for turbine intakes at dams to decrease mortality of downstream migrating juvenile salmonids. This paper provides a history of the extensive research to accomplish this goal. [ABSTRACT FROM AUTHOR]

Abstract: Snake River stream-type Chinook salmon smolts migrate >1000km from rearing habitats to the Pacific Ocean and return 1–3 years later for their upstream spawning migration. Construction of 8 mainstem dams on the Snake/Columbia River that fish must pass has greatly altered the connectivity between their freshwater spawning and rearing habitats and the ocean. In addition to direct mortality to smolts passing through turbines, these dams along with over 200 additional dams and storage reservoirs above them affect the volume, timing and turbidity of river flows and the size of the plume entering the ocean. At mainstem dams, improvements to fish ladders have largely eliminated problems for upstream migrants, while construction of screened bypass systems, a spill program, and transport of smolts by barge have greatly improved direct survival of juveniles. However, smolt-to-adult returns have not shown the same improvement and have been highly variable in recent years. While direct survival for juveniles passing 8 dams is now as high or higher than historically when they passed only 4, survival downstream of the last dam has changed in part due to altered timing and condition of smolts upon ocean entry. Recent additions of surface passage structures at dams have reduced travel time through the system to more closely approach historical rates prior to dam construction. However, substantial additional improvement in direct survival of smolts through the hydropower system does not appear achievable with existing knowledge and technology. Restoring conditions in the plume might improve survival but would require increased flow volume. [Copyright &y& Elsevier]

Effective conservation and management of natural resources requires accurate predictions of ecosystem responses to future climate change, but environmental science has largely failed to produce these reliable forecasts. The future response of Pacific salmon ( Oncorhynchus spp.) to a changing environment and continued anthropogenic disturbance is of particular interest to the public because of their high economic, social, and cultural value. While numerous retrospective analyses show a strong correlation between past changes in the ocean environment and salmon production within the north Pacific, these correlations rarely make good predictions. Using a Bayesian time-series model to make successive 1-yr-ahead forecasts, we predicted changes in the ocean survival of Snake River spring/summer chinook salmon ( O. tshawytscha) from indices of coastal ocean upwelling with a high degree of certainty ( R2 = 0.71). Furthermore, another form of the dynamic times-series model that used all of the available data indicated an even stronger coupling between smolt-to-adult survival and ocean upwelling in the spring and fall ( R2 = 0.96). This suggests that management policies directed at conserving this threatened stock of salmon need to explicitly address the important role of the ocean in driving future salmon survival. [ABSTRACT FROM AUTHOR]