We used the gravel sampling equipment and 

 procedures described by McNeil and Ahnell 

 (1964) to collect and determine the size of the 

 bottom materials. The choice of individual 

 plots to be sampled in each area was nnade 

 by drawing paired numbers from a table of 

 random numbers (Snedecor, 1956) and plotting 

 the coordinates on a mapof the stream. Sample 

 plots were located in the stream by pacing 

 the distance from a baseline set up along the 

 stream. Samples of gravel were taken from 

 the upper intertidal area before and after 

 spawning to learn if spawning activity reduced 

 the amount of fines (silt and fine sand passing 

 through 0.833-mm. sieve) in the streambed. 

 The other areas in Olsen Creek were sampled 

 only after spawning and served as a basis for 

 comparing the areas. Middle Slough and Little 

 Creek were both sampled before spawning. 

 Samples were randomly chosen within the 4- 

 to 10-foot (1.2- to 3.0-m.) tide levels because 

 there is no spawning below or above these 

 levels in these two streams. 



The mean percentage of fines in the upper 

 intertidal area was significantly higher before 

 spawning (11.0) than after spawning (7.4--see 

 table 2), ' but the reduction may have been 



^ The respective variances were 20.8 and 4.7. A com- 

 parison of the two means was made with the t-test. Be- 

 cause the sample sizes were different and the variances 

 were unequal, the degrees of freedom were calculated by 

 the formula given by PauUk. The t-value of 3.13 (26 d.f.) 

 was significant at the 99-percent level. (Gerald PauUk. 

 1961. Two-sample statistical tests. Univ. Wash., Seattle, 

 Fish. Res. Inst., Clrc. 155, 7 pp.) 



caused by flooding rather than spawning. 

 McNeil and Ahnell (1964) demonstrated that 

 both flooding and spawning activity reduced 

 the percentage of fine nnaterials in astream-- 

 and several freshets occurred during Septem- 

 ber in Olsen Creek (fig. 2). 



The area where Olsen Greek meets tide 

 water serves as a settling basin, and in general 

 the percentage of fines increased from the 

 higher to the lower tide levels (table 2). An 

 exception to this progression was the low- 

 gradient area, where the stream is deeper and 

 has less gradient than in the two adjoining 

 sections. 



The percentage of live eggs in the stream 

 in the fall and the survival of larvae over the 

 winter decrease from higher to lower tide 

 levels in Olsen Creek (Helle et al., 1964), 

 This trend in mortality is probably caused 

 not only by lower streambed permeability but 

 also by the increasingly severe effects of 

 tide-associated changes in salinity, dissolved 

 oxygen, and temperature in the lower inter- 

 tidal zone. 



ESTIMATING ABUNDANCE OF SPAWNERS 



An estimate of the number of spawners is a 

 basic statistic in studies on the life history 

 of pink salmon. Such estimates are often made 

 by counting salmon at weirs as they pass up- 

 stream to the spawning grounds. The use of 

 weirs to study intertidal spawners at Olsen 

 Creek is impractical, however, because of the 

 width of the intertidal spawning area; more- 



Table 2. — Mean percentage by volume of bottom materials that were retained by various sieves and settled from 

 suspension in 10 minutes, from four areas of Olsen Creek, Middle Slough, and Little Creek, 1962 



Sample area 



Samples 



Total volume retained by sieves with 

 square mesh openings (in mm.) of-- 



50. S' I ^S.4 I 12.7I6.S5I 5.36 11.68 1 5.SJ3|0.4i7| Ci.2oS | 0.104 



Total volume 

 of solids 

 settling from 

 suspension 



Fines 

 ( amount passing 

 through 0.833- 

 mm. sieve) 



Number 



Per- 

 cent 



Per- Per- Per- Per- Per- Per- 

 cent cent cent cent cent cent 



Per- 

 cent 



Per- 

 cent 



Per- 

 cent 



Percent 



Percent 



Olsen Creek inter- 

 tidal zone 



Upper 



intertidal^ 



22 9.3 17.5 16.3 14.8 13.0 9.5 8.5 5.0 2.2 



0.7 



Upper 



intertidal' 12 6.1 16.2 18.9 18.0 15.1 9.9 8.5 4.1 1.3 0.7 



Low gradient 10 4.8 20.7 21.1 16.0 11.4 7.2 8.6 5.0 2.9 1.3 



Middle 



intertidal 43 5.7 18.4 19.7 16.2 13.6 9.3 7.8 4.0 2.0 0.8 



3.1 



1.3 



1.2 



2.4 



11.0 



7.4 

 10.4 



9.2 



Lower 



intertidal 



Middle Slough 



Little Creek 



29 3.5 15.4 19.1 16.1 13.5 10.2 8.9 

 25 2.6 11.2 17.6 19.3 16.2 10.0 8.9 

 25 1.8 18.5 23.8 21.7 16.1 5.5 3.3 



^ Rooks larger than 10 am. minimum dimension excluded. 

 ^ Sample taken before spawning. 

 -" Sample taken after spawning. 



