SPAWNING AND SETTING OF OLYMPIA OYSTERS 
449 
Table 4. — Comparison of average monthly values of salinity and pH in a dike in Oyster Bay and one in 
Mud Bay during 2 years 
Date 
Oyster Bay, dike 5 
Mud Bay, dike B 
Date 
Oyster Bay, dike 5 
Mud Bay, dike B 
Num- 
ber of 
sam- 
ples 
Aver- 
age 
salin- 
ity 
Aver- 
age pH 
Num- 
ber of 
sam- 
ples 
Aver- 
age 
salin- 
ity 
Aver- 
age pH 
Num- 
ber of 
sam- 
ples 
Aver- 
age 
salin- 
ity 
Aver- 
age pH 
Num- 
ber of 
sam- 
ples 
Aver- 
age 
salin- 
ity 
Aver- 
age pH 
1932 
1933 
4 
26. 93 
8. 00 
3 
27. 75 
8. 00 
January 
4 
24. 02 
7. 87 
4 
26. 49 
7. 90 
February 
3 
25. 99 
8. 00 
4 
25. 76 
7.98 
February. ... .. 
3 
25. 68 
8. 10 
4 
25. 25 
8. 10 
5 
24.47 
8. 08 
4 
25. 37 
8. 00 
March 
3 
24. 70 
8. 17 
2 
26. 84 
8. 10 
3 
22. 67 
8. 20 
3 
27. 52 
8. 30 
April 
5 
25. 86 
8.30 
4 
24.92 
8. 26 
May 
7 
26. 17 
8. 00 
4 
24. 05 
8. 10 
May 
11 
26. 39 
8.20 
7 
24.91 
8. 12 
9 
27.31 
7.91 
9 
25. 84 
7. 88 
June 
12 
27. 36 
7. 97 
12 
25. 65 
8. 05 
July 
13 
27. 88 
7. 85 
12 
25. 93 
7.90 
July 
12 
28. 11 
7. 92 
13 
26. 68 
7. 88 
11 
28. 05 
7. 74 
10 
26. 53 
7. 84 
August. 
11 
28. 21 
7. 96 
13 
26. 97 
7. 94 
8 
28. 67 
7. 80 
10 
28. 00 
8. 00 
September 
6 
28. 29 
7. 93 
7 
26. 99 
7.96 
7 
28. 49 
7. 85 
4 
28. 64 
7. 87 
October.. 
4 
27. 49 
7.90 
4 
23. 59 
7. 90 
4 
27. 88 
7. 90 
5 
27. 39 
7. 92 
November 
4 
24. 45 
7.80 
4 
27. 42 
7. 75 
December 
2 
26.39 
7. 85 
2 
27. 48 
7.80 
December. 
3 
24. 64 
7.80 
1 
26. 36 
7. 80 
In Mud Bay, however, into which more fresh water flows, there is a distinct 
gradient (table 3) in the salinity of the water at low tide in a series of 4 dikes from the 
shore (dike A) to the edge of the 
channel (dike D). The first three 
dikes are on the same level but the 
last ( D ) is about 1 foot lower. The 
lower level does not account for the 
salinity difference. The main body 
of fresh water from creeks at the 
head of the bay follows the channel, 
while the contours of the bay tend 
to carry the more saline water at 
flood tide to the west side of the bay. 
The variation in salinity between 
individual samples taken at any 
time is relatively slight and the val- 
ues over a period of a year may be 
best indicated by monthly averages. 
In table 4 the average monthly sa- 
linity and pH are given for 2 full 
years, 1932 and 1933, in two typical 
dikes, dike 5 in Oyster Bay and 
dike B in Mud Bay. The summer 
samples refer to conditions at low 
tide when the dikes were exposed. 
During the rest of the year the values 
refer only to bottom samples taken 
at relatively high tide. The more 
clearly to represent seasonal varia- 
tions, the data are plotted in figures 
8 and 9. The lowest salinity occurs 
generally during late winter and 
early spring, depending upon the time of greatest precipitation, and the annual varia- 
tion, expressed in this manner, is usually between about 24 and about 29 p.p.mille. 
The salinity on the oyster grounds in Mud Bay is more variable than in Oyster 
Bay, as may be seen by comparing the figures, and heavy rains affect the water more 
quickly in the former. The hydrogen-ion concentration varies in a more orderly 
Figure 8. — Average values of salinity and pH of water on oyster ground 
(dike 5) in Oyster Bay during 2 years. Most summer samples were 
taken at low tide while during the remainder of year bottom samples 
were taken. Compare with Mud Bay, figure 9. 
