Biological Effectiveness of 2005 Summer Spill

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In October 2005, the Independent Scientific Advisory Board (ISAB) received a request from the Northwest Power and Conservation Council (Council) to review the biological effectiveness of court-ordered summer spill operations in 2005 for benefit/recovery of ESA-listed Snake River fall Chinook. The National Marine Fisheries Service (NMFS) and the Columbia River Inter-Tribal Fish Commission (CRITFC) approved the ISAB's assignment and added questions for the ISAB to consider in its review.

The 2005 court-ordered spill began on June 20 at the four lower Snake River dams and continued through August 31. At McNary Dam on the Columbia River, court-ordered spill was initiated on July 1 and continued through August 31. A large majority of the subyearling fall Chinook hatchery production fish emigrated through the lower Snake River prior to initiation of the spill, but a majority of the wild subyearling fall Chinook were exposed to the spill.

The ISAB found several studies relevant to the effect of the 2005 court-ordered summer spill on juvenile subyearling salmon survival, travel time, dam passage, and smolt to adult return rates (SARs). However, none of these studies was specifically designed to examine how summer spill may benefit recovery of ESA-listed Snake River fall Chinook. The attached report provides the ISAB's findings on the contribution of these studies to the understanding of the biological effectiveness of 2005 summer spill. The ISAB report also includes recommendations for additional research, monitoring, and evaluation studies needed to determine the efficacy of summer spill.

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