189 



'How can diuns kill 95 percent of juvenile 

 salmon if 85 percent of them are transported 

 alive'' 



Fish collection and transpoitaiion caifie less 

 than 1 percent mortality for salmon and steelhead. 

 The overall effecDveness of the smolt 

 transportation program has been evaluated by 

 NMFS for several years. NMFS scientists estimate 

 that adult survival rales for transported fish arc 

 about 60 to ISO percent higher than for ftsh that 

 pass directly through the hydroelectric dams and 

 reservoirs. Although there is some conjecture over 

 a possble latent nsottality of transported fish, all 

 recent transportation studies indicate a beneficial 

 effect for transporting juvenile salmoa 



Below Bonneville Dam, the Estuary and the 



Ocean: 



Percentage of total mortality - 25% (A.E.)* 



From below Bc»ineville Dam and through the 

 estuary, both tnusported and non-transported fish 

 are exposed to high levels of predation and other 

 mortality factors. After Bonneville dam it is 

 difficult to monitor juvenile salmon, however, 

 some analyses suggest about a 40 percent mortality 

 through this river reach. 



In the ocean, mortality is high for all Snake 

 River salmon stocks. Of those juvenile fish that 

 enter the Pacific Ocean, only 1 to 5 percent will 

 survive to return as adults headed back up the 

 Columbia River. Most of the ocean morality is 

 believed to occur during the early months of ocean 

 entry. 



It has become increasingly evident that ocean 

 ecological and enviroiunental conditions play a 

 major role in determining ocean survival, for both 

 wild and hatchery stocks. For example, amilar 

 population trends have been observed between 

 Snake River spring chinook and other West Coast 

 chiiKX>k populations of both dammed and 

 urvdammed river systems. The poor returns of 

 chinook salmon in the early 199(ts are to a large 

 extent due to [>oor ocean conditions, whether or not 

 the fish encountered dams. 



Snake River spring chinook are estimated to 

 have little direct and secondary nxinaliiv due to 

 open ocean fishing, about a 1-3 per • mortality 

 rate. But under historical fisheries i i policies, 

 adult fall chinook mortality was appi nately 35 

 to 40 percent, with most harvest occurring in 

 Canadian waters. 



AduU Uv-River Passare SurvivaL 

 PercenUge of total mortality - 10% (A.E.)* 



Once in the river, returning adult chirKiok 

 salmon will experience mortality from natural 

 causes, dam passage, and harvest impacts. Adult 

 up-river passage mortality is estimated to average 

 about S percent per project through the 

 Columbia/Snake river system, due to both natural 

 and man-made causes. For Snake River fall 

 chinook, about 28 percent are harvested as 

 'incidental take' within the livlian and non-Irxlian 

 conunercial fisheries. 



Pre-Soawnine Stafe: 

 Percentage of total mortality ' 



15% (A.E.)* 



The final mortality stage occtus as adults leave 

 the upper dam. Lower Granite and make their final 

 ascent to the spawning grounds. Here survival rate 

 estimates vary gready, ranging from between 60 to 

 85 percent Among the different salmon runs, 

 spring chinook are estimated to have the lowest 

 pre-spawning survival rate as they travel almost 

 400 miles in this final stage. 



aj:. 



Wbat is Adult Equivalent? 



Snake River salmon mortality is best 

 described by comparing mortality across 

 different life stages in equivalent terms. To 

 do this, the value of a fish within certain 

 life-stages must be "calibrated" to its 

 expected value as an adtilt spawner. For 

 example, given the life<ycle survival rate 

 information described above, it is apparent 

 that a large number of smolts entering the 

 Lower Snake River system (above Lower 

 Granite Dam) is required to produce one 

 returning adult spawner. But in a later life 

 stage, a smaller number of fish is required 

 to pnxluce one returning adult spawner. 



83-191 0-94-7 



