::i 



CALIFORNIA PISH AND OAME 



The rate of appearance above the gravel is of considerable inter- 

 est and i.s shown in Figure L3 as the total oumber of fry for all 

 seven control nests with respect to the time of emergence. The peak 

 emergence, as shown by the slope of the curve, occurred 20-22 days 

 alter appearance of the firsl Pry. The rate then decreased until the 

 last fish appeared on the forty-fourth day. Table (i includes the date 

 and number of fish appearing from all control nests. 



a* 



10 15 20 25 30 



EMERGENCE PERIOD - DAYS 



Fig. 13 



35 



40 



45 



In no case was the recovery of live fry plus fry and eggs in the 

 gravel greater than 158 out of 500 originally placed in each nest. 

 The recovery of relatively few eggs therefore indicates that undeveloped 

 ones had decomposed and disappeared, as would be expected. The 

 number of fry that hatched but died without working up through 

 the gravel was relatively small. 



Yield of Fry— Early Silt Addition 



Table 2 shows the essential data for the seven nests of Trough 2 

 which received mining silt for varying time periods from the beginning 

 of the experiment. The yield of Try from nest 7 is not included since 

 this nest was dug into and the deposited silt flushed off on March 9th, 

 when it was though! no fry were going to emerge from this series. 



The average yield of 1.1<i', \'vy from this series is so low that 

 comparisons between nests do not appear warranted. The outstanding 

 fact is that silt added during the initial stages of incubation and con- 

 tinued for either a few days or a Longer period, causes severe damage 

 resulting in low yields of fry. The emergence of \'vy above the gravel 



