88 



Irrigation diversion — ^ ' 



(NMFS Photo) l^^^^^l^ 



,:^ 



Setting a purse seine 

 (NMFS Photo) 



wide geographic area and for an extended period of time. 

 Annual variability and the possible presence of long-term 

 trends in the ocean environment make it difficult to detect 

 changes in survival that result from agencies' efforts to 

 improve inland conditions. 



When the salmon begin their upstrejmi migration as adults, 

 they again face harvest by commercial and recreational 

 fisherman and predation by marine mammals. Passage 

 through the dams also presents a problem. Biologists are 

 able to count salmon as they use the dams' fish ladders on 

 their way upstream. Large numbers of salmon "disappear" 

 in between dams. The reasons these adult fish disappear 

 include: mortality, uiireported and illegal harvest, fish 

 falling back over the dams after being counted in the fish 

 ladder of a previous dam, straying or wandering, and 

 spawning in reservoirs and their tributaries. 



The causes of mortality include: predation and wounding by 

 marine mammals, injuries from fishing gear, water 

 pollutants, exposure to water supersaturated with dissolve*: 

 gases, high water temperatures, large spillway discharges, 

 diseases, and other mortality. Additional mortality may 

 result from injuries received when the fish "fall back" 

 downstream and go through turbines, bypass systems, 

 spillways, or navigation locks. 



When the adult salmon return to the area where they 

 emerged from their parents' redd, they again face habitat 

 problems. Spawning beds may be silted in with sediment 

 from logging, mining, or roadbuilding, or the water may be 

 too warm for them. In addition, human activities may 

 unintentionally scare them away from the spawning beds. 



