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The following points further describe in detail the scientific rationale for initiating and 

 continuing the program: 



* Controlled spill as provided by the program, with the stringent monitoring protocols 

 included, provides the best possible means of passage survival for downstream salmon 

 migrants. ' Extensive studies at mainstem dams throughout the basin document that juvenile 

 mortality from spUl ranges from 0-3% ( NWPPC 1986; Raymond 1988; Holmes 1952; 

 Ledgerwood 1990; Iwamoto et al. 1993). 



* Other passage routes through dams cause higher levels of mortality. Turbine passage causes 

 from 10-20% direct mortality (NWPPC 1986; DFOP 1993). Mechanical bypass systems, not 

 installed at all dams, only guide and collect 35-70% of juvenile migrants. Mortality to 

 juvenile spring chinook that are guided by mechanical bypass systems ranges from 1-3% 

 (Monk et al. 1991; Dawley 1991; FTOT annual rqxirts; Krema et al. 1986; and Brege et al. 

 1987). 



* Spill disperses predators from the forebay and tailrace areas (Faler et al. 1988) 



* There is considerable evidence that juvenile fish can detect and avoid high levels of gas 

 supersaturation (Dawley et al. 1975). 



* After installation of the spill deflectors in the mid 1970's, the historical record demonstrates 

 that better adult returns followed from juveniles which migrated under high flow and high spill 

 conditions (Fish Passage Center SOR-19 1994). 



* Four of the five best adult return ratios for Snake River spring and summer spring chinook 

 from 1974 to 1989 occurred in 1975, 1982, 1983, and 1984. Spill levels during these years 

 were substantially higher than those currently being implemented. 



* When compared to past years, the levels of spill being implemented in 1994 axe 

 substantially less than what occurred in the late I970's and early 1980's. These levels are not, 

 "unprecedented" as described by the federal operators. 



* Levels of spill proposed for 1994 are considerably less than those that occurred in 1993, a 

 year in which nmoff levels late in the spring chinook migration resulted in high spill rates. In 

 1993, no fish with signs of impacts of gas supersaturation were detected through the Smolt 

 Monitoring Program until spill levelsgreatly exceeded those proposed for 1994 . The 

 monitoring program showed tiiat in spite of high spill (which occurred during flows that were 

 more than twice the levels anticipated for 1994) the observed impacts of dissolved gas on fish 

 were minor (DFOP 1993, Appendix 6). 



Prq)ared by the stafEs of: National Marine Fisheries Service, United States Fish and Wildlife 

 Service, Columbia River Inter-Tribal Fish Commission, Idaho Department of Fish and Game, . 

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



SCEENTmC RATIONALE FOR IMPLEMErOTNG A SPELL PROGRAM Page 2 



