133 



SCEENTDFIC RATIONALE FOR IMPLEMENTING A SPILL PROGRAM TO 



INCREASE JUVENILE SALMON SURVIVAL IN THE SNAKE AND 



COLUMBIA RIVERS 



- The foUowing summarizes the scientific basis for implementing a spiU program during 

 12 nighttime hours at all Corps of Engineers dams on the mainstem Snake and Columbia 

 Rivers to increase protection for 1994 spring outmigrating juvenile salmon. As concluded by 

 the peer review team of indqiendent scientists, "[t]ransportation alone, as presently conceived 

 and implemented, is unlikely to halt or prevent the continued declined and extirpation of Usted 

 species of salmon in the Snake River Basin" (Mundy et al. 1994). Spill at transportation and 

 coUector dams, whfle continuing to transport those fish coUected by the mechaiucal bypass 

 system addresses fte substantial uncertainty associated with the effectiveness of the juvenile 

 transportation program (TRG 1993; Mundy et al. 1994). A management approach when faced 

 with uncertainty is to spread the risk between two choices. The spill program is designed to 

 improve in-river passage survival and spread the risk by leaving a larger percentage of juvenUe 

 salmon migrating in-river. For the last several years, substantial spiU for juvenile migrants has 

 been implemented at aU mid-Columbia PubUc Utility District projects. As well, substantial 

 controUed spill has been routinely implemented at Corps projects including Lower 

 Monumental, Ice Harbor, The Dalles, and Bonneville Dams as an effective management 

 strategy to increase juvenile salmon survival. 



The objective of the spill program is to safely guide 80% of the juvenile migrant 

 salmon away from the turbines, the most harmful passage route at the dams, and pass them 

 through mechanical bypass systems and over the spiUways. Spill volumes will be controlled to 

 avoid harmful levels of dissolved atmospheric gas in the river. 



The current spiU program at the mainstem Corps dams was jointly coordinated and 

 devised by fishery scientists from the National Marine Fisheries Service, the United States 

 Fish and Wildlife Service, the Oregon Department of Fish and Wildlife, the Washington 

 Department of Fish and Wildlife, the Idaho Department of Fish and Game, and.the Columbia 

 River Inter-Tribal Fish Commission. The spill program has been adopted for the remainder 

 of the 1994 spring outmigration. This may be one of the major options, evaluated in the long 

 term as part of an adaptive management approach, used to assist in improvmg juvenile survival 

 with respect to recovery. 



Fishery agendes and tribes have chosen a conservative approach to the implementation 

 of the spill program. Where possible, based on real time and historical salmon migration 

 patterns, spill is generally being confined to nighttime hours. This substantially limits 

 economical impacts of spill because power demand is much less at night and nver flows are 

 lowered at night. An extensive program for monitoriiig the signs of gas supersaturaaon 

 impacts in both juvenile and adult salmon has been estabUshed with trained biologists at each 

 dam. The spill program can be immediately modified based upon the daily results of the 

 monitoring program. 



SCIENTIFIC RATIONALE FOR IMPLEMENTING A SPDLL PROGRAM . Page I 



Attachment 6 



