Scientific Background
Recent evidence suggests that improvement in survival of the estuarine and early ocean life history phase of Columbia River salmon may be critical to recovery of endangered stocks. When coupled with evidence that the estuary and the plume (as an extension of the estuary) may be highly modified habitats due to river modifications (e.g. altered channel morphology) and modified flows as a result of the federal hydropower system, potential for achievable improvement in salmon survival from management actions seems plausible. An understanding of which factors affect survival will require a partitioning of survival (and mortality) among freshwater, estuarine, and early ocean phases. This in turn will require knowledge of the processes that limit and/or enhance salmon survival in these habitats. These processes, though well characterized in the freshwater environment, have not been characterized in the estuarine and plume environment. Since 1998, we have been evaluating the Columbia River plume as a critical habitat for juvenile salmon. Here, we request a continuation of this work, with modifications based on findings to date.

The Columbia River is a major source of salmon to the sea, thus first principles dictate that it is logical to focus a major effort on studies of the salmon-plume interactions, particularly during May and June when out-migrating Columbia River salmon are first entering the sea.  Locally, the Columbia River plume, as a natural extension of the estuary, represents a habitat of less saline marine waters that is hypothesized to be critical to salmon survival when they are making the transition from freshwater to saltwater. This is supported by recent studies assessing the importance and impact of river plumes to salmon survival. The mechanisms by which the Columbia River estuary and plume may affect juvenile salmon survival have not been determined, but likely include provision of food resources, a refuge from predators due to the turbidity (thus low visibility) in the plume, and a refuge from coastal predators due to rapid transport offshore and away from the coastal zone by the riverine plume.

The shape and extent of the Columbia River plume is controlled largely by the amount of freshwater flowing out of the Columbia River. The timing and amount of flow affects the amount of sediment (and turbidity), as well as the amount of nutrients which fuel estuarine and oceanic productivity. Flow regulation, water withdrawal and climate change have reduced the average flow and altered the seasonality of Columbia River flows, changing the estuarine ecosystem). Annual spring freshet flows through the Columbia River estuary are ~50% of the traditional levels that flushed the estuary, and total sediment discharge is ~1/3 of 19th Century levels. Decreased spring flows and sediment discharges have also reduced the extent, speed of movement, thickness, and turbidity of the plume that once extended far out and south into the Pacific Ocean during the spring and summer.

An emphasis on survival of salmon in the estuarine and marine environment is warranted because approximately half of all pre-adult (egg through juvenile stage) salmon mortality occurs there. Variability in ocean salmon survival is very high, ranging over three orders of magnitude over the past three decades for coho (PSFMC unpublished data 1995). Abiotic and biotic ocean conditions are highly variable as well, and undoubtedly account for the large range of juvenile salmon ocean survival. Long-term regime shifts in climatic processes and El Niño and La Niña events affect oceanic features and can produce abrupt differences in salmon marine survival and returns (Francis and Hare 1994). One of the latest recognized regime shift occurred in the late 1970s and may have been a factor in reduced ocean survival of salmon in the Pacific Northwest (PNW) and increased survival in Alaska during the period 1977-1998. Recent changes in ocean conditions, which began in late 1998 provide evidence of a possible new regime shift that is favorable to salmon survival in the Pacific Northwest. The evidence for a new more favorable regime ended abruptly in 2005, however, leading to an ocean off the west coast that was unfavorable to salmon growth and survival with subsequent salmon harvest closures extending from Washington to California occurring in 2008. Improving ocean conditions began to resurface in 2008, but may reflect the impacts of impending climate change, i.e ocean conditions that switch from good to bad more frequently than observed in the past century. This provides evidence for the increasing need to monitor and provide timely information to managers of the current ocean conditions and likely impact on survival and eventual abundance returns of adults back to the Columbia River basin.

Our recent work in the plume and adjacent coastal zone has now shown that the northern California Current experiences 'regime shift' at a higher rate of periodicity which is due in large part to changes in the length of the upwelling season, with concurrent change zooplankton biomass has in the coastal waters off Oregon, and a change in community composition related to the dominance of cold water species, and eventual change is salmon survival that can range five-fold. Therefore, it is important to keep in mind that the plume and plume dynamics are modulated by climate influences at decadal to shorter time scales as well as inter-annual, seasonal and daily scales depending upon the strength of the upwelling process. Thus, plume-ocean interactions are a key component of our research program.

In September 2010 and May/June of 2011, efforts will focus on three sampling cruises to assess the abundance and distribution of Chinook and coho salmon and steelhead stocks originating from the Columbia River Basin to extend the time series begun in 1998. Complimentary information on the associated pelagic fish community, including piscine predators, and the oceanographic conditions will be collected that will be used to refine and identify the controlling factors in the early ocean environment (including the plume) that affect the growth, survival, and eventual return of adult salmon back to the Columbia River Basin. The information generated will be used to forecast eventual adult returns one to three years in advance of their actual return.