EFFECT OF MINING SILT ON YIELD OF FRY FROM SALMON BEDS 35 



is also retarded, as a period of 19 days totalling 393 temperature 

 unite elapsed between the first appearance in the gravel controls and 

 this series. The last fry emerged on April 15th. In general these 

 fry were smaller and weaker than those of the control series and a 

 number of deformities were noted. 



TABLE 2 



Effect of Mining Silt During Early Stages of Incubation — Trough 2 



*2-4 hours daily. 



The larger number of whole eggs remaining in the gravel at the 

 conclusion of this experiment is significant as it shows a tendency for 

 undeveloped eggs to resist decomposition apparently due to a pro- 

 tective coating of silt. The number of fry remaining in the gravel was 

 small but totaled more than the fry that emerged and may therefore 

 indicate difficulty in working through the deposited silt. 



A comparison of the fry from the control neste and this series as 

 shown in the photograph, Figure 14, reveals the striking reduction 

 in yield from mining silt. As previously explained, the fry from nest 7, 

 series 2 should be disregarded. 



Series I. Control — No Silting 

 12 3 4 5 6 7 



•# * 



J *^^T ^P 7 ^|r TK 



^v 



* , $r 



Series II. Mine Silt Added 



Fig. 14. Showing the marked difference in yield between the Control, Series I, and 



Series II, with early silt addition. 



Yield of Fry— -Late Silt Addition 



The yield of fry and the number of eggs recovered from the nests 

 of Trough 3 follow a definite, consistent pattern and are of particular 

 interest and significance. Table 3 shows the data for this series which 



