PRODUCTION AND COLLECTION OF SEED OYSTERS 
247 
time of spawning was found to vary somewhat in accordance with water temperature 
and tidal conditions. Heavy and complete spawning of the harbor oysters occurred 
on July 13 in 1925, but not until August 1 in 1926, and July 22 in 1927. The spawn- 
ing in 1925 was over two weeks earlier than the average time of spawning observed 
during the past seven years and was due to the higher water temperature and the 
early ripening of the oysters during July of that year. The heaviest spawning was 
found to occur after the water had reached and maintained a temperature of from 
20° C. to 21° C. for a few days. During all three years the spawning took place at 
the end of the “full moon tidal period” or in other words from seven to eight days 
after the time of the July full moon. It was observed also that the oysters spawned 
near and at the time of high tide, when the water was found to be more alkaline and 
had a pH value of 7.8 and above. On the days when spawning occurred it was found 
that the water had attained for the first time (since ripening of the oysters) an average 
temperature of 20.7° C. 
LARVAL PERIOD 
Quantitative plankton collections were made regularly to study the occurrence 
and distribution of the oyster larvae. In these collections the larvae were found to 
be relatively scarce and in many cases were totally absent. The number of larvae 
collected in the harbor was extremely small in proportion to the intensity of setting 
which occurred there later. For example, the total number of larvae collected over 
the spawning bed in a period of several weeks scarcely reached a hundred, while in 
the same spot many hundred thousand were later found attached to the collectors. 
In a series of plankton collections made during several tidal cycles it was found that 
the oyster larvae were most abundant at the time of low slack water and gradually 
disappeared as the tide began to run flood. The distribution of the larvae in relation 
to the stage of tide on August 11 to 13, 1926 is shown in Figure 30. When the flood 
current had developed a velocity of 18.3 centimeters (0.6 foot per second, practically 
no larvae could be found swimming in the water while samples from the bottom collected 
at the same time were found to contain an average of 14 larvae per square foot of 
surface. The finding of the oyster larvae on the bottom at certain stages of the tide 
shows that they are not passive planktonic forms and, therefore, are not subject to 
wide dispersal by the tides and currents. By remaining on the bottom during the 
greater part of the larval period and by limiting their summing activities to thedidal 
periods when horizontal movement of the water is leas , the oyster larvae are able to 
remain and set on and near to the spawning bed which produced them. 
One of the important questions that has presented itself in the development of 
methods for seed oyster production has been, “Where does the spawn, or larvae, 
from a bed of oysters finally become attached or set?” The increased production of 
oyster larvae and spat in Milford Harbor following its rehabilitation showed definitely 
during the past three years that the oyster larvae are not distributed far from the 
spawning bed by the currents — the predominating drift of which is out of the harbor. 
The final distribution of the larvae was determined easily by studying the relationship 
of the setting areas to the spawning bed. It was found that the majority of the larvae 
set within a radius of 300 yards from the center of the spawning bed, and that the 
greatest number of spat per square inch or per shell was found on the bed and within 
a 100-yard radius. As indicated by setting, the larvae were distributed both above and 
below the spawning bed and attached in greater numbers on the areas which were 
just below or in the direction of the sound. Though the intensity of setting varied 
