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Fish Passage Center Responds To ISAB Review Of Delayed Mortality Memos; Focus On ‘Weight Of Evidence
Posted on Friday, October 21, 2011 (PST)

Recent technical memorandums issued by the Fish Passage Center served as warnings, though not the final word, that latent/delayed mortality caused by passage down through the mainstem Columbia-Snake river hydro system may occur in salmon and steelhead, according to an Oct. 13 FPC memo responding to a critique from the Independent Scientific Advisory Board.


The Sept 16 ISAB review said three FPC technical memos issued over the past year “are reasonable and scientifically defensible based on the data used.”


“However, other reasonable conclusions could also be reached, and issues remain concerning the data used.


“Based on our review, the studies and analyses cited in these technical memos do not provide an adequate base of reliable information to support a ‘weight of evidence’ conclusion on the strength of a relationship between multiple bypass passage and latent mortality of juvenile chinook and steelhead,” the ISAB memo says. “That is, the relationships observed between latent mortality and bypass passage are confounded with other factors that obscure unambiguous interpretation.”


The FPC memos explore the issue of whether or not migrating juvenile salmon suffer from latent/delayed mortality as a result of passage through mechanical bypass systems or turbines or from being collected and transported downstream aboard barges.


The memorandums, produced in response to queries from state and tribal fish management officials, cited numerous studies as supporting the conclusion that delayed/latent mortality does occur and result in lesser smolt-to-adult return rates.


(For more on the ISAB review of the memos see CBB, Oct, 14, 2011, “ISAB Reviews Fish Passage Memos On Long-Standing Issue Of Delayed Mortality In Migrating Salmon”


The FPC in a response to the ISAB review said it “purposely did not include any reference or conclusions regarding ‘weight of evidence’ of latent and delayed mortality associated with powerhouse passage of juvenile salmon and steelhead.


“FPC memorandums included reference to ‘a broad scope and range of evidence’ that indicate that latent/ delayed mortality occurs as a result of powerhouse passage,” the Oct. 13 FPC memo says.


“Weight of Evidence (WOE) is a formal evaluation procedure for integrating the results of multiple measurements in environmental risk assessments. A weight of evidence approach takes into account the strengths and weaknesses of different measurement methods when determining whether results indicate a harmful environmental effect.


“A formal weight of evidence evaluation, whether qualitative or quantitative provides a framework for rigorous consideration of the strengths and weaknesses of various measurements and of the nature of uncertainty associated with each of them (Massachusetts WOE Workgroup 1995).


“The Fish Passage Center memorandums reviewed by the ISAB did not mention either weight of evidence or the larger objective of weight of evidence approaches, risk assessment,” according to the recent Fish Passage Center memo. “The Fish Passage Center memorandums concluded and we continue to maintain, that there is a broad scope and range of evidence that indicates that delayed/ latent mortality is occurring in juvenile salmon and steelhead that experience powerhouse passage. The ‘weight of evidence’ objective pursued by the ISAB in their response was neither the objective of the FPC memorandums nor possible from a review of study results.


“The FPC conclusions and the ISAB response, particularly regarding confounding factors, both point to the need to address the delayed/ latent mortality associated with powerhouse passage in a formal WOE retrospective ecological risk analysis. The FPC memorandums provide the basis for the pursuit of a weight of evidence approach, if the management agencies agree that the evidence discussed and the ISAB review comments, particularly regarding confounding factors, raises adequate concern,” the Oct. 13 memo says.


“…the strengths, weaknesses and implications of data and analyses relative to delayed mortality from powerhouse passages would be appropriately considered in a formal WOE ecological risk assessment, which is beyond the scope of the FPC memorandums.”


“As technical staff to fishery management agencies and tribes, the FPC has the responsibility of raising potential fish passage problems and issues to the managers,” the FPC memo says. “The FPC memorandums function to alert the managers that evidence for delayed mortality associated with powerhouse passage is developing and requires attention.


“The indications of delayed/latent mortality associated with powerhouse passage are present in many different analyses by many different researchers. This raises a concern. Whether or not these issues are pursued, addressed or resolved is the purview of the fishery managers.”


The memo from FPC manager Michele DeHart to the Fish Passage Center Oversight Board Chairman Bruce Measure and ISAB Chair Rich Alldredge says “The ISAB did not present any evidence that latent/delayed mortality is NOT associated with juvenile passage through powerhouses. The ISAB review only raised potential confounding factors. The ISAB review never indicates or infers or presents analyses indicating that delayed/ latent mortality does not occur as the result of powerhouse passage.


The FPC was created through the Northwest Power and Conservation Council’s fish and wildlife program process with the charge of providing technical assistance and information to fish and wildlife agencies in particular, and to the public in general, on matters related to water management, spill and other fish passage measures. The board is made up of representatives of the Council, NOAA Fisheries Service, state fish and wildlife agencies, basin tribes and the public. Measure is also NPCC chair.


The memos, as well as the ISAB review, can be found at the FPC web site,


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