SPAWNING AND SETTING OF OYSTERS 
63 
The general size range of the larvse in each sample was determined by measuring 
the length of a number of specimens with a micrometer scale. The purpose was 
primarily to obtain an idea of the age, or growth stage, of the larvae. In Figure 6 
graphs are presented to show both the relative abundance and the size range of 
larvae taken in plankton collections in Offatts Bayou from April 1 until the end of 
August. Collections during the latter part of April and the beginning of May were 
infrequent, but the results of these samples are entirely consistent. It will be observed 
that during early April larvae in the collections were not abundant, indicating that 
spawning had not reached its maximum. After the middle of April, however, the 
curve is very high showing the great abundance of oyster larvae. This abundance of 
larvae continued until the middle of June and from then until the end of August, 
when collections were discontinued, the number of larvae taken became constantly 
less numerous. 
Figure 8. — Chart showing the relative abundance of oyster larvae and diatoms, in 
plankton samples taken at stations 1 to 5 (figs. 4 and 5), as averages of all collections 
during each month from May to August. Relative abundance is designated by 
ordinates as in Figures 6 and 7. The rapid disappearance of diatoms is contrasted 
with the relatively slow reduction in number of larvae taken 
The period of greatest abundance of larvae in the water appears to have been 
from the middle of April to the middle of June. Since these larvae were predominantly 
in the straight-hinge stage, or within about 3 days old presumably, the records may 
be considered to indicate the period of most profuse spawning. However, in July 
and August spawning continued, as shown in Figure 6, at a diminished rate, and 
almost every collection contained larvae. The collections made at the Deer Islands 
(fig. 7) were essentially similar to those made in the bayou, as described above, though 
few samples were taken before the end of May. 
Figure 8 is presented to show the monthly average abundance of larvae taken in 
collections at stations 1 to 6. The abundance of diatoms is also given in this figure. 
(See section on diatoms.) Stations 1, 2, and 3 were in the bayou; station 4 in West 
Bay outside the bayou inlet; and stations 5 and 6, which are averaged as of one station 
numbered 5, at the Deer Islands. (See charts, figs. 4 and 5.) The relative abundance 
of larvse at each station was determined by averaging the figures designating the 
abundance of larvse in all collections taken at each station during each month, from 
44569—31 2 
