Mef:hod8 



Individual salmon nesting sites were counted and recorded for eaoh 

 riffle. An area of suitable spaiming gravel, 9 by 7 feet in extent, 

 measured lengthwise with the current, was considered as one nesting site. 

 Major criteria used to define suitable nesting gravel were t (1) depth 

 of water (0.5 - 1.5 feet), (2) sire of gravel (1-5 inches in diameter), 

 (3) its location on the riffle, and (4) estimated current velocity. 

 Application of these criteria to Individual riffles was conditioned by 

 combinations of many influences. Greater water velocities enable success- 

 ful spawning in the areas where gravels are large. With lesser current veloci- 

 ties, these areas are not suitable. Under certain circumstances, water 

 deeper than 0«5 - 1.5 feet is certainly used. Some riffles consist of 

 suitable gravel, current velocities are satisfactory, and water depths 

 are within the range stated, but the entire riffle may be compacted and 

 cemented so that it cannot be used by spawning salmon. Broad standards 

 of estimate were set for these sui*veys. However, much of the accuracy 

 achieved necessarily depended on the experience and Judgment of personnel* 



On riffles with scattered patches of suitable gravel between large 

 boulders, each individual nest site was picked out and counted. The area 

 of riffles with larger rocks scattered throughout suitable spawning gravel 

 was determined and reduced by a correction factor, the correction factor 

 was found by coxinting the individual nesting sites on an average cross 

 section of the riffle and comparing the count with the niaaber possible if 

 the entire riffle were suitable gravel. On riffles with greatly varying 

 gravel types, two or more such corrections were made as the riffle changed 

 in character. The areas of riffles composed entirely of suitable gravel were 

 divided into 9 by 7 foot sections. The number of sections was oonsidered to 

 be the spawning capacity. 



Results of Surveys 



The first 1945 spawning bed survey was started in July when the river 

 was flowing 350 cubic feet per second at the Lewiston gauge* The survey was 

 completed 10 days later when the flow at Lewiston was 250 cubic feet per 

 second. Slight corrections were made to compensate for variable flows so 

 that the entire survey would show as nearly as possible the number of ne3ts 

 at a flow of 300 cubic feet per second. 



The second spawning bed survey was conducted during the middle of 

 September when the river discharge at Lewiston was 100 cubic feet per second. 

 Results of these surveys are presented in "Pable 17, which gives the number of 

 nests counted and the comparative efficiency of water and riffle usuage for 

 spawning at the two flows, expressed in nests per cubic foot per second per 

 Bile of stream. 



In areas where there are broad riffles of fine gravel, the efficiency 

 of water and riffle usage increases with increased water flow. This la 

 particularly true of the stretch of river between Grass Valley Creek and 

 Douglas City (Figure 10) where many broad, shallow riffles are converted 

 to good spawning sites by increased flows* Just the opposite is true of 

 narrow riffles where the spawning efficienoy is reduced by increased flow* 



51 



