Among other findings, a temperature block to migration 

 was revealed at the point the Snake River enters the Co- 

 lumbia. In the exceptionally warm summer of 1967, fish 

 bound for the Snake River were delayed at the confluence 

 for about 8 weeks — the river temperature was 7° F. higher 

 than normal. 



Future studies will use sonic tags to test the efliciency 

 of collection systems at fish ladders, to measure fallback 

 of salmon through spillways at dams, and to study behavior 



of salmon that encounter hot water discharges from ther- 

 mal nuclear plants. 



Sonic tracking was pioneered 15 years ago by our lab- 

 oratory, primarily as a means of studying the behavior of 

 salmon in their natural environment. Biologists within and 

 outside the Bureau have since adapted similar equipment 

 and techniques to the study of other aquatic animals — as 

 diverse as lobsters, turtles, and whales. 



MIGRATIONS OF JUVENILE FISH 



In their migration from the spawning area to the sea, 

 young fish face a harsh and dangerous journey. As they 

 move downstream, their survival depends upon the availa- 

 bility of food, their ability to avoid large hungry fish, and 

 finally the influences created by obstacles man has placed 

 in the rivers. Each new dam and reservoir adds to the 

 journey's hazards. 



Our research on juvenile fish examined the effects of 

 alterations of the physical and biological environment and 

 developed methods to assist the fish in their migration and 

 increase their survival. Young fish — wild and hatchery- 

 reared — were captured, marked with a cold brand or mag- 

 netized wire tags, and released at various locations on the 

 Snake and Columbia Rivers (fig. 31). As the runs moved 

 downstream, the fish were recaptured in floating traps and 

 other collection devices in the rivers and at dams. Near 

 the end of their migration they were sampled by beach (fig. 

 32) and purse seines in the estuary. Evaluations of mi- 

 gration and survival were based on the numbers of marked 

 fish recovered at various points. Biologists studied the ef- 



- 140 Miles to Estuary 

 Uom Bonneville Oom 



• RECAPTURE SITES 

 A MARKED FISH RELEASE SITES 

 >DAM 



FIGURE 31. -Study areas in Columbia River system. 



fects of temperature and of excess nitrogen on juvenile fish. 

 Turbine studies assessed losses of fish and devised systems 

 to reduce mortalities. In other research, migrating fish were 

 deflected by moving screens or transported around potentially 

 dangerous areas. 



24 



