EFFECT OF MINING SILT ON YIELD OF FRY FROM SALMON BEDS 39 



earlier silt additions extending back into the incubation period pro 



dueed progressively lower yields which reached 



beginning of the incubation period. In this 



undeveloped eggs thai were coated and preset 



steadily with earlier and longer periods of si 



fish that hatched failed to emerge but many 



forward through a screen rather than upward 



deposited silt. 



zero with silting at the 

 series the number of 

 ved with silt increased 

 It addition. Very few 

 fry apparently worked 

 through the gravel and 



<nV^3 



ESS 



SILT EMERGENCE 



PERIODS 



YIELD 



1 



BASKET 

 INCUBATION 



M „ 'PERIOD OF EXPERIMENT- DAYS 

 NESTI 



FINAL PERCENT 

 YIELD OF FRY FROM EGGS 



Fir:. 17. Graphic summary showing- 19 nests of the experiment, with days to emer- 

 gence of first fry, total emergence periods, and yield from each nest of 

 unsilted gravels (Trough 1) and silted gravels (Troughs 2 and 3) as com- 

 pared with hatching time of 30-38 days in hatchery baskets ("Basket 

 Incubation") which yielded 79.9% fry. Delayed emergence and decreased 

 yields are particularly evident for Trough '1, with early silt additions. 



