EFFECT OF MINING SILT ON YIELD OF PET PROM SALMON BEDS 31 



fourth trough 13,600 additional 



eggs 



were placed in each of two 



standard hatching baskets for determining the time of hatch and yield 

 of fry under the usual hatchery procedure. 



Addition of Mining Silt 



The seven nests of Trough 1 received only the hatchery supply of 

 water without addition of mining silt and served as a control for 

 determining the yield of fry from salmon eggs in unsilted gravel beds, 

 and also provided a comparison with the normal basket hatch. 



For producing turbidity in the 14 nests of Troughs 2 and 3, wet 

 mining silt was secured from the settling ponds of the Pacific Placers 

 Engineering Company on Arkansas Creek, a tributary of the Cosumnes 

 River. This material was typical of the fine silt and slimes discharged 

 by gold dredging operations in many California mining areas. Figure 

 12 is a photograph showing the crew collecting this material. 



Fig. 12. Crew collecting mining silt for experiment. 



Two to three buckets of the wet slimes were agitated in a barrel of 

 water by means of a recirculating pump and the addition of a small 

 stream of water from the hatchery supply produced a muddy overflow 

 which was led to the desired point of application by a small wooden 

 flume installed between experimental Troughs 2 and 3. Fed in the 

 manner described, the above quantity of silt lasted 2 to 4 hours after 

 which the experimental nests received only hatchery water until the 

 following day. 



The silt laden water from the flume was introduced at the desired 

 nest by boring f" holes in the side of the flume. Outlets not in use 

 were plugged with rubber stoppers. The muddy water was always 

 added between nests and above the baffle board in order to cause mixing 

 with the hatchery water before reaching the adjacent gravel nest. 



In Trough 2 the turbid water was started above the first nest on 

 January 7th, the initial day of the experiment. Entering at this point, 



