EFFECT OF MINING SILT ON YIELD OF FRY FROM SALMON BEDS 37 



were found to be alive. In general these fry were small, poorly 

 developed or deformed. 



Series III 

 12 3 4 5 6 7 



Fry that worked through gravel beds 



"m- 1 



Eggs and fry in beds at conclusion of experiment 



Fig. 15. Showing the relation between emerging fry and silt-coated eggs remaining 

 in the gravel of Series III. Fry in Bed 1 should be disregarded as explained 

 in text. 



The effect of silting on yield is strikingly revealed in Figure 16 

 which is a composite photograph showing fry that emerged from the 

 gravel controls and all the silted nests combined with charts showing 

 incubation, emergence and silt periods. In this connection it should be 

 noted that the horizontal line for first emergence applies to the gravel 

 control rather than the silted nests. 



Figure 17 shows graphically the normal time of basket hatch in 

 relation to period of emergence, time of silt additions, and yield of 

 live fry for the 19 gravel nests on which full data were secured. 



Summary, Conclusions and Recommendations 



1. Salmon eggs hatched in the usual manner by placing a basket 

 of eggs in the flowing water of a hatchery trough produced a yield of 

 79.9% fry with 733 temperature units. 



2. Salmon eggs placed in prepared gravel beds constructed in a 

 hatchery trough and receiving only normal hatchery water produced 

 a maximum yield of 25.4% and an average yield of 16.2% fry. 

 Occasional silting of the water supply due to storms may have lowered 

 the yield. To first emergence from the gravel 992 temperature units 

 were required. 



3. Salmon eggs in prepared gravel beds that received mining silt 

 for intervals of 2 to 72 days beginning with the initial stages of incu- 

 bation produced a maximum yield of 2.4% and an average yield of 

 only 1.16% fry. A total of 1385 temperature units were required to 

 first emergence from the gravel. Many of the undeveloped eggs 

 remaining in the gravel were preserved with a coating of silt. Fry 

 that died or failed to emerge outnumbered those that worked through 

 the gravel. 



4. Salmon eggs in prepared gravel beds that only received mining 

 silt during the emergence period produced a yield of 13.4% fry but 



