FISHERY BULLETIN: VOL. 76. NO. 3 



Figure l. — Daily number of 1967 

 brood year pink salmon fry counted 

 through Sashin Creek weir in spring 

 1968. 



25 5 15 25 



MARCH APRIL 



15 

 MAY 



25 



5 15 



JUNE 



Mortality Patterns in the Streambed 



Mortality of eggs and alevins within the 

 streambed at Sashin Creek is evident in two ways: 

 1 ) as a reduction in the total population of eggs and 

 alevins within the streambed, i.e., they disappear, 

 and 2) as an increase in the number of dead eggs 

 and alevins in the streambed and a decrease in the 

 number of live eggs and alevins. In the first in- 

 stance, some factors that can cause eggs and ale- 

 vins to disappear are turbulent streamflow, 

 streambed scouring, predation, and scavenging. 



Excluding predation, these same factors can also 

 cause dead eggs and alevins that may have died for 

 other reasons to disappear from the streambed. In 

 the second instance, factors causing an increase in 

 the number of dead eggs and alevins within the 

 streambed are generally relatable to desiccation, 

 freezing, and the quality of intragravel water. 



In addition, dead eggs and alevins may disap- 

 pear because of at least two factors that do not 

 affect live eggs and alevins: biochemical decom- 

 position and consumption by intragravel inver- 

 tebrate scavengers. Thus, factors that cause eggs 



574 



