SPAWNING AND SETTING OF OLYMPIA OYSTERS 
445 
A graph (fig. 5) is reproduced to illustrate the daily maximum, minimum, and aver- 
age temperatures during winter (December 1932, January and February 1933) and 
summer (June through August 1933). This well represents the extremes, for during 
summer, at low tide, the water frequently reached 25° to 30° C., and during winter 
dropped to almost —2° C., or close to the freezing point of seawater. In the latter 
instance a great many oys- 
ters which were not well 
covered with water of high 
salinity were frozen and 
killed. The minimum tem- 
perature during summer and 
the maximum during win- 
ter show only slight fluc- 
tuations, since in summer 
the extreme low tides are 
during the day and in win- 
ter at night, the local tem- 
perature of the air not 
greatly affecting that of 
the water around the oys- 
ters at high tide. The 
difference between winter 
maximum and summer min- 
imum is about 10° C. 
In order to show in detail 
the changes in water tem- 
perature in the dikes dur- 
ing a 24-liour period, as in- 
fluenced by the range of 
tide, a graph (fig. 6) is given 
on which the continuous 
temperature records during 
4 days are reproduced. 
Neap tide and spring tide 
temperature records are 
shown for typical days dur- 
ing both winter and sum- 
mer. In the record for Au- 
gust 2 it will be noted that 
during the several hours 
that the dike was exposed 
by a —1.7-foot tide the 
temperature rose gradually 
from about 19° to about 30° C., and that when the flood tide poured over the 
dike the temperature dropped about 5° almost instantly. The other summer record 
was taken a few days later when low tide occurred at about 5 o’clock of a cool 
morning, and although the dike was not quite exoosed there was a marked drop in 
temperature. The picture for temperature variations during winter is almost the 
reverse, the low tide occurring at night when the air is coolest. In all cases the 
149604—37 2 
DECEMBER JANUARY FEBRUARY 
Figure 5. — Daily average, maximum, and minimum temperature on an oyster bed in 
Oyster Bay during winter and summer, as shown by thermograph records. 
