FIGURE 42.— Hydraulic chamber for studying response of fish 

 to pressure changes. 



Activity 



An activity detector (fig. 43) measured the movements of 

 juvenile fish during 24-hour periods. Coho and sockeye 

 salmon were active from sunset till midnight, whereas 

 Chinook salmon were generally more active during daylight. 

 Activity seemed to be regulated by biological clocks which 

 told the fish when the sun rose and set even though they 

 were in a darkened indoor tank. 



FIGURE 43.— Periodic activity of juvenile sockeye salmon being 

 measured in laboratory apparatus. 



Shear Forces and Cavitation 



Hydraulic shear forces, at the margins of highly turbulent 

 water, can be created by turbine blades at dams. In the 

 laboratory, fish were killed by momentary contact (1/1,000 

 second) with differences in water velocity of 16 feet per 

 second or higher. These sharp velocity differences may 

 occur in small areas that measure less than 2 inches; fish 

 have no defense against such forces. This action suggests 

 that shear forces may be a major hazard to fish in turbines. 



The sudden collapse of vajwr i)ockets caused by cavitation 

 in the highly turbulent water around moving turbine blades 

 has been suggested as a major source of injury. Cavitation 

 effects have been known to pit steel and erode concrete. 

 In the laboratory, however, fish exposed to sudden collapse 

 of simulated vapor pockets were unaffected by pressure 



— 32 



