248 
BULLETIN OF THE BUREAU OF FIS HE RIES 
from year to year the distribution of the larvae was always found to have this same 
relation each year to the spawning bed. 
Figure 30. — Oceu’* ce of oyster larvae in plankton in relation to the stage of the tide 
The duration of the larval period (from spawning to setting) was found to vary 
from 13 to 18 days. The variation in the larval periods observed during 1925, 1926, 
and 1927 is given in the following table. 
Table 27. — Duration of larval periods , 1925-1927 
Year 
Length of period 
Mean 
tempera- 
ture of 
water, 
° C. 
Remarks 
1925 - 
13 days (July 7-20) 
20.8 
20.6 
21.3 
23.2 
20.0 
21.2 
Following light spawning. 
Following heavy spawning. 
Following light spawning. 
Following heavy spawning. 
Do. 
1925 
16 days (July 13—29) 
1926 - 
16 days (July 21-Aug. 6) 
1926 
15 days (Aug. 1— 16)_I 
1927--- 
18 days (July 1-Aug. 8). 
15.6 days 
In many cases the failure of setting has been attributed to a mortality of larvae 
as a result of sudden changes in temperature or salinity and to heavy rainstorms. 
