Table 3. — Ninty-five-percent confidence interval estimates of 



mean dissolved oxygen content of inlragravel water in study 



streams 



(Water samples were collected 7 to 10 inches beneath the stream bed surface. 

 All values are given as mg./l.] 



through 1960 are shown in figure 6. Oxygen 

 levels were severely depressed in 1957, and high 

 mortality of 1957 brood year eggs occurred. The 

 relation between mortality and oxygen levels will 

 be discussed later. 



COMPOSITION OF BOTTOM MATERIALS 



There were marked differences in size composi- 

 tion of bottom materials among the study streams. 

 The bed of Indian Creek contained greater quan- 

 tities of coarse materials and smaller quantities of 



O ^ 



Ld 



O 



£ 6- 



rr 



Ld 



O 



z < 



Lul § 



£^ 



x w 



°£ 



UJ (5 ? _ 

 >< Cr 



Q 



fine materials than the beds of either Harris River 

 or Twelvemile Creek. The bed of Twelvemile 

 Creek contained considerably more silt than the 

 beds of Indian Creek or Harris River. Table 4 

 lists the average size composition (by volume) of 

 bottom materials in each of the study streams. 



The volume of fine materials in salmon spawn- 

 ing beds is inversely related to the permeability of 

 bottom materials (McNeil and Ahnell, 1964). 

 Figure 7 shows the observed relation between the 

 percentage of bottom materials by volume passing 

 through an 0.833-mm. sieve and the coefficient of 

 permeability. 



The observed mean percentages of solids passing- 

 through an 0.833-mm. sieve are listed below for the 

 study streams in order of decreasing permeability : 



Percent 



1 . Intertidal Indian Creek 9 



2. Upstream Harris River 14 



3. Intertidal Harris River 1" 



4. Intertidal Twelvemile Creek 18 



.5. Upstream Twelvemile Creek 19 



McNeil and Ahnell (1964) found that the finest 

 fractions contained the highest percentages of 

 organic detritus. It will be assumed, therefore, 



600 



500 



o 

 >- 



b 400 - 



< 



Id 



rr 



LlJ 



q. 



o 

 u. 



Ll 



Ul 



O 

 O 



300 



200 



100 



1956 1957 1958 1959 I960 



5 10 15 20 25 



PERCENTAGE OF BOTTOM SAMPLE BY VOLUME 

 PASSING THROUGH 0.883-MM. SIEVE 



Figure 6. — Approximate mean dissolved oxygen content 

 of intragravel water in the three study streams (Harris 

 River, Indian Creek, and Twelvemile Creek) near the 

 beginning of the spawning period (1956-60). 



Figure 7. — Relation observed between coefficient of per- 

 meability and the fraction by volume of a bottom sam- 

 ple passing through an 0.833-mm. sieve (from McNeil 

 and Ahnell, 1964). Curve fitted by eye. 



SPAWNING BED ENVIRONMENT OF PINK AND CHUM SALMON 



507 



