446 
BULLETIN OF THE BUREAU OF FISHERIES 
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variation is slight except at low tide when the water is shallow and readily reacts to 
sunshine and atmospheric conditions. That is, it is the surface water which responds 
readily to weather condi- 
tions; and the oysters may 
be under 16 feet of water at 
high tide and 3 or 4 inches 
a few hours later. 
Seasonal variations in 
water temperature from 
year to year are relatively 
uniform, but the differences 
between successive seasons 
are sufficient to have a con- 
siderable bearing upon the 
spawning of oysters. In 
table 1 the monthly aver- 
ages for 4}i years are given, 
as calculated from thermo- 
graph records obtained in 
Oyster Bay. The highest 
average water temperature 
is usually in August, the 
lowest in January or Feb- 
ruary. The annual variation is represented graphically in figure 7 for the 2 years 
(1933, 1934) when the temperature values were most widely different from one 
another. The spring rise in the 
curve for 1934 occurred about a 
month earlier than in 1933, account- 
ing for a comparable difference in 
the time of spawning. Included on 
the graph are monthly averages of 
daily readings of maximum and 
minimum air temperature at 
Olympia. These records were sup- 
plied through the kindness of 
Charles F. Norrie, official weather 
observer. Water temperature 
is clearly correlated with air 
temperature. 
Other aspects of the tempera- 
ture conditions are considered in later sections referring to the comparison of 
Oyster and Mud Bays in salinity, pH, and temperature. 
Table L - — Average monthly water temperature in dike in Oyster Bay, calculated from thermograph 
records 
[Temperature °C.] 
Figure G. — Reproductions of portions of thermograph records showing variations in 
water temperature on oyster ground during four 24-hour periods, two in summer 
and two in winter. The most variable records refer to spring tides, the others to 
neap tides. Time and height (in feet) of high (H) and low (L) tides are indicated. 
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Figure 7.— Average monthly temperature of water on oyster grounds 
during 2 years as related to monthly averages of maximum and min- 
imum daily air temperature at Olympia. 
1932 
1933 
1934 
1935 
Month 
1931 
1932 
1933 
1934 
1935 
7. 28 
7. 70 
9. 38 
7. 66 
July 
18.2 
18. 10 
18.71 
19.27 
19. 48 
6.36 
6. 07 
10. 07 
8.88 
August . . . 
18. 45 
18.61 
19. 12 
19. 79 
19. 45 
8. 56 
9. 30 
11.83 
9. 22 
September _ 
17. 04 
17.09 
16. 07 
18.60 
10.61 
11.76 
12. 03 
13. 15 
14.61 
13.69 
13.90 
15.41 
14. 02 
13.06 
15. 46 
9. 92 
11.70 
11. 78 
11.41 
8. 95 
17.00 
16.64 
17. 67 
17. 93 
December 
7. 88 
7.89 
9.61 
9.78 
9. 38 
Month 
January,. 
February. 
March 
April 
May 
June 
