SPAWNING AND SETTING OF OYSTERS 
71 
laboratory and examined carefully for spat. By constantly placing fresh, clean bags of 
shells on the beds adequate cultch was always available for larvae of the setting stage. 
In this manner the possibility of the shells becoming too slimy to act as suitable set- 
ting places was eliminated. As a further control the oysters and shells of the natural 
reefs were examined from time to 
time in order to be sure setting was 
not taking place on those instead 
of on the planted shells. Bags 
of shells were periodically planted 
from early in March until late in 
August and examined for spat. 
When it was found that the 
bags of shells bore spat, several 
such bags from the same place were 
examined to see roughly if the spat 
were of the same approximate size 
and abundance. Then all of the 
shells in one bag, or in two from 
the same place, were carefully 
examined and counts made of the 
total number of spat on the inside 
surfaces of the shells. Since this 
method requires the counting of 
young and minute spat it was not possible to make counts for more than a half bushel 
of shells in each case. Only those on the inside surfaces of the shells were counted 
because the outside surfaces of the shells were too rough to permit accuracy. 
The counts made are compar- 
able, however, and refer to the 
number of spat on the inside sur- 
faces of a half bushel of shells. 
The counts were more accurate 
for spat several days old than for 
those only one or two days after 
setting, because the latter were 
readily sloughed off in handling, 
especially after the shells had be- 
come dry. 
GROWTH OF SPAT 
• 2 3 4 5 6 7 6 9 10 II 12 13 14 15 
TOTAL LENGTH OF SHELL (MILLIMETERS) 
Figure 13. — Showing average daily growth in length of shell of oyster 
spat in relation to total length. The growth rate increases slightly 
with size. An ideal line is drawn to serve as a basis for calculations 
) 22 24 26 26 30 32 
SPAT IN DAYS 
In the counts above described 
it would occur that the spat 
might range from less than 1 
millimeter to 6 or 8 millimeters in 
length, the shells having been in the 
water for two or three weeks. It was considered desirable to attempt to define the 
intensity of setting more closely than over two or three week intervals. A roughly 
serviceable method was devised to give the number of larvse setting daily at each 
Figure 14.— Showing length of shell of oyster spat in relation to age, 
calculated from values on the ideal line in Figure 13. The curve, 
for growth of spat of the ages shown departs only slightly from a 
straight line 
