THE EFFECT OF MINING SILT ON YIELD OF FRY 

 FROM SALMON SPAWNING BEDS 1 



By Paul A. Shaw and John A. Maga, Pollution Detail, 

 California Division of Fish and Game 



Introduction 



The silting of stream beds from mine tailings has long been 

 regarded as deleterious to the development of salmon spawn, but little 

 data have been available to show the extent of this damage. Ellis 

 (1937), a recognized authority on stream pollution, states that "erosion 

 silt and other suspensoids affect fisheries directly by covering the bot- 

 tom of the stream with a blanket of material which kills out the 

 bottom fauna, greatly reduces the available food, and covers nests and 

 spawning grounds * * *." On the other hand, a study sponsored 

 by the Oregon State Department of Geology and Mineral Industries 

 (Ward, 1937-1938) asserts that mining activity was not found to be 

 damaging to fish life on the Rogue River. This latter publication has 

 been extensively quoted in California to combat control measures 

 advocated by recreational groups and the Division of Fish and Game 

 in the interest of clean streams and conservation of aquatic life. 



In view of the extensive mining activity along trout streams and 

 within watersheds that are essential to the maintenance of California 

 salmon and steelhead, an experimental study was conducted to aid in 

 settling the existing controversy and establish a factual basis for ade- 

 quate but just enforcement action. 



The experiments were conducted between January 7th and April 

 15, 1941, at the Brookdale Fish Hatchery, Santa Cruz County, Cali- 

 fornia, and were planned in a manner to determine the yield of fry 

 from salmon eggs in gravel nests subjected to mining silt as compared 

 to the yield from similar nests without silt additions. 



"While the authors planned and supervised the investigations here 

 recorded, they are greatly indebted to the late James L. Stinnett, 

 hatchery foreman, and James Hinze, fish hatchery assistant, for aid 

 in all phases of the work. These men handled the spawning operations, 

 conducted a basket hatch control, and carried out the daily work of 

 adding silt, adjusting water flows, recording temperatures, and collect- 

 ing and counting' fry as they emerged from each gravel nest. Leo 

 Shapovalov, senior fisheries biologist, supervised the handling, counting 

 and placing of the fertilized eggs in the gravel beds. Warden Donald 

 Hall, of the Pollution Detail, located the site for collection of the mining 

 silt, and personnel from the Central Valleys Hatchery transported the 

 necessary amount from the Cosumnes River watershed to the Brookdale 

 Hatchery. 



1 Submitted for publication October, 1942. 



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