NATURAL HISTORY OF THE BAY SCALLOP 
599 
REPRODUCTION AND DEVELOPMENT 
SPAWNING PERIOD 
A knowledge of the spawning period of a species may be important for various 
reasons. For a commercial form it often is essential for conservation (as by legal 
regulations). Much of the life history and biology must remain obscure until this 
period is determined, at least in part. It may be of considerable theoretical interest. 
For the bay scallop all of these apply. 
A spawning period may be determined in various ways. It may be possible to 
determine it, at least in part, by direct observation or by watching the animal spawn. 
By examination of the gonads and noting when they first show ripe sexual products, 
first show evidence of discharge of sexual products, and when the gonads become emp- 
tied, the beginning and end of the period may be determined. However, to learn 
the time of principal and effective spawning, it generally is necessary systematically 
to collect eggs, larvae, or 
MY 
AUG 
5 EFT 
OCT 
NOV 
DEC 
JAN 
FES 
Figure 19. — Graph based on largest scallops of 1926 year class obtained during fall 
of 1926 and a portion of succeeding winter. The junction of trend with base 
line was taken to indicate approximately the beginning of spawning 
young, noting when these 
first appear in numbers, 
become abundant, decrease 
and disappear. 
Some information was 
obtained by the first two 
methods. Seldom is it 
practicable to collect iamel- 
lib ranch eggs. For reasons 
that will be discussed later, 
collections tor larvae gave 
little aid. By far the best 
evidence as to principal time 
of spawning came from col- 
lections for small scallops 
beyond the larval stage. 
In North Carolina very small scallops seldom, if ever, become so numerous as 
to be in evidence amidst the vegetation to which they attach, and it was not till the 
fall of 1926 that methods were developed which gave satisfactory data as to their 
abundance. The method consisted in collecting and drying a tub of eelgrass and 
other vegetation from the flats, screening the siftings from the vegetation, and exam- 
ining the screenings for scallops. The material retained by the finer screen was 
examined under a binocular. At that time young of the year already had attained 
considerable size. Very small scallops continued to be found abundantly until 
February 2, 1927, decreased in March, and became rare in April. (See fig. 20.) Al- 
though the age of these small scallops was not definitely known, from consideration 
of growth rate and from observations on scallop gonads, it was concluded that impor- 
tant spawning continued into January. An attempt was then made to determine 
the beginning of spawning. From semimonthly size-frequency curves (5 millimeter 
groupings) the “first appearance” of scallops in succeeding size groups was noted. 
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