US Army Corps of Engineers ®

FACT: Unexplained mortality of juvenile fish does not correlate with direct mortality due to the hydro system.

More Information: Federal biologists with the Corps of Engineers say the validity of the analysis is questionable and has a number of drawbacks.

• The paper is based on the Plan for Analyzing and Testing Hypothesises (PATH) analysis from several years ago. This information, along with more recent data that reflects several years of healthy fish returns during favorable ocean conditions, was fully considered by the National Marine Fisheries Service (NMFS) during preparation of their 2000 Biological Opinion on operation of the Federal Columbia River Power System (FCRPS). NMFS stated that current estimates of differential mortality (D-values) have wide confidence intervals and D-values are critical uncertainties to be resolved. The Corps is currently funding research to address this.

• Extra mortality is all unexplained mortality or unknown errors in the life cycle regression model, as well as any survival differences between the Snake River and lower river stocks in juvenile rearing and outmigration, ocean, adult migration through the lower river, and adult spawning. In PATH, it was shown that this extra mortality varies on a year-by-year basis and is not correlated with direct mortality due to the hydro system. This is inconsistent with the authors' hypothesis that adverse hydro passage conditions are the cause of the extra, or unexplained, mortality.

• The analysis relies on a comparison of Snake River stocks to lower river stocks. This is not a valid assessment of the effects of dams because of numerous other conditions that vary between these groups, including species composition, community structure, wild/hatchery composition, fish size, habitat type and condition (geology, hydrology, ecology, land use), migration timing and distribution in freshwater and estuary/ocean, etc. The data used for this comparison contains inconsistencies in sampling, many assumptions, and poor documentation.

• No empirical data was presented to assign losses to the hydro system in the authors so-called "evidence". Where they do refer to selected data (e.g., Figure 5), it is based on sample sizes (0 to 19 returning adult fish) too small to draw meaningful conclusions.

• Mortality occurs naturally within the salmonid life cycle, a fact ignored in the paper's hypothesis, which attempts to attribute mortality solely to hydro.

• There are numerous errors in fact and in citations and many statements that lack supporting citations. Some examples:

  • Page 38 - The authors cite the statement "a considerable proportion of fish are delayed in the forebay for a week or more& " from one paper. Since this study, numerous similar, but more robust, evaluations on the Columbia River have occurred that refute this statement. For example, the worst case scenario on the lower Columbia River would occur at John Day Dam, where median forebay delay ranges from 0.3 to 8.9 hours. At the Dalles Dam, median forebay residence time has ranged from 0.3 to 2.3 hours.

  • Page 39 - The authors state that fish that pass dams through spillways avoid mechanical injury and severe pressure changes inherent in other routes. This is false. Direct testing shows as much or more mechanical injury at spillways as through turbines. At all of the spillways, surface-oriented fish must sound to depths greater than 10 meters, surfacing immediately after they pass through the spill gates.

  • Page 39 - The authors say "hydrosystem operation and its effects on the estuary and near-shore environment may affect salmonid survival by altering the annual flow cycle& .". This is not related to "Evidence Linking Delayed Mortality of Snake River Salmon to Their Earlier Hydrosystem Experience".

  • Stress Section - The authors' own statements that "interpretation of their (stress results) significance remains difficult", "documenting stress may be difficult", and " relating the level of mortality brought on by stress may be even more problematic," illustrate the speculative nature of their conclusions.

  • Indirect Evidence - The authors ignore recently-published information that demonstrates that different fish stocks experience different ocean survival rates, because of migration to different ocean areas. This may be a more plausible explanation for the stock performance differences presented in this paper.

  • Direct Evidence - The authors cite a NMFS manuscript, but the years and results cited do not match the information presented in that NMFS report and, in fact, contradict some of NMFS results.