HOOPES: SELECTION OF SPAWNING SITES 

 18- 



16- 



14- 



z 



UJ 



o 



UJ 



a. 



(/) 

 a 

 a 



UJ 



a: 



Q. 



o 

 <_) 

 o 



_i 

 < 



o 



12- 



10- 



8- 



6- 



4- 



2- 



1959, N=2, 925 



— I960.N = 544 

 .-1961, N = 859 



—I 1 1 1 1 1 1 



10 20 30 40 50 60 70 80 90 100 



DISTANCE FROM STREAM MOUTH (PERCENT) 



Figure 2. — Distribution of redds occupied by sockeye 

 salmon in Hidden Creek, Brooks Lake, Alaska, during 

 the 1959, 1960, and 1961 spawning seasons. 



16 



14 



12- 



1959, N=530 



I960, N=528 



1961, N= 199 



;i 



I I 

 I I 

 I I 

 I I 

 I I 

 I I 

 I I 

 I I 



100 



DISTANCE FROM STREAM MOUTH (PERCENT) 



Figure 8. — Distribution of redds occupied by sockeye 

 salmon in Up-a-tree Creek, Brooks Lake, Alaska, during 

 the 1959, 1960, and 1961 spawning seasons. 



in water velocity and in the average size of bot- 

 tom particles. 



PHYSICAL CHARACTERISTICS OF 



STUDY STREAMS IN RELATION 



TO SPAWNING 



To determine relationships between the loca- 

 tion of spawning sites and physical character- 

 istics of the streams, I measured the gradient, 

 size composition of the bottom materials, and 

 water depth and velocity of spawning areas in 

 the three streams. Velocity and volume of 

 streamflow, stream width, and stream gradient 

 are known to affect the size composition of ma- 

 terials in the streambed, but velocity is consid- 

 ered to be the dominant factor (Krumbein and 

 Pettijohn, 1938; Rubey, 1938; Hjulstrom, 1939; 

 Krumbein and Sloss, 1951). A reduction in 

 stream gradient is accompanied by a reduction 



STREAM GRADIENT 



Gradients were measured in each study 

 stream from the mouth to the first beaver dam 

 judged normally impassable to migrating salm- 

 on. Gradients were calculated between con- 

 venient points (stations) that were 100 to 200 m 

 apart along the stream. The relative elevation 

 of the water surface was measured with a sur- 

 veyor's level, and the distance between stations 

 was measured along the center of the streambed 

 with a surveyor's chain. Stream width was also 

 measured at each station. The survey sections 

 were numbered consecutively upstream from the 

 mouth of each creek. 



Survey sections were often too long to reveal 

 variations in gradient and distribution of spawn- 



451 



