NATURAL HISTORY OF THE BAY SCALLOP 
625 
second season, but what portion normally would do so, or the extreme age attained, 
is not known. Slow-growing scallops that are small when 1 year old may be large 
when 2 years old. 
A prominent line, reasonably termed a 1-year line or annual-growth line is formed 
in the fall and followed by notable winter growth. It is tentatively assumed to be 
due to some metabolic activity connected with egg and sperm development. On the 
upper valve it is a light line on a dark ground. 
Scallops seldom are found far from grassy bottom. It is here suggested that this 
is because eelgrass and associated vegetation comprise the most favorable objects 
of attachment for the young and because thereafter scallops usually shift but little. 
Depth is not found to be very important except as shallow water exposes the 
scallops to the attacks of enemies and the effect of unusual cold. 
No close correlation is found between growth and salinity. Scallops taken in 
water of a winter salinity of 20 parts per mille to 21.6 parts per mille were larger than 
those from some areas where much higher salinities prevail. Although scallops have 
been found, in poor condition but alive, in water of a salinity as low as 13 parts per 
mille and although there is evidence of plentiful survival at least by the young of 
reductions nearly to this figure, considerable mortality presumably attributable 
to low salinity in certain instances has followed reductions to about this concentra- 
tion. The delay between water freshening and scallop death may be great. A 
reduction to 6 parts per mille at Pivers Island was almost if not quite completely 
destructive, at least of adults. Moderate mortality in Beaufort Plarbor followed a 
reduction in the fall of 1928 not known to have gone below 18.5 parts per mille. The 
lowest concentration observed over scallop beds except in time of extreme freshets 
was 20 parts per mille, the highest observed 38 parts per mille. 
From field observations it is concluded that among the physical factors affecting 
scallop growth, current is most important; the faster the current the more rapid the 
growth and the larger the market scallops. 
Perhaps because of the rapid growth and early maturity and the absence of any 
prolonged period of water temperature sufficiently low to inhibit feeding no direct 
correlation between temperature and growth is found. The only consistent growth 
line appears typically in the fall, occasionally in the summer, and always by early 
winter. It can be accounted for on a temperature basis only on the supposition that 
temperature drop or loss of summer warmth temporarily causes growth cessation. 
This does not seem probable. 
Enemies possibly are most destructive during larval and prelarval stages, but 
there is indication of very heavy mortality of scallops less than 10 millimeters long. 
Of the forms which prey upon adults and juvenile the best known are the starfish, 
the oyster drill, and the herring gull. Of these the herring gull is much the most 
conspicuous. In the limited but valuable areas subject to exposure at ordinary 
ebb tides it is considerably destructive. No evidence was found of serious destruc- 
tion of scallops by oyster drills, and it is believed that the slow-moving drill ordinarily 
is not an important scallop enemy. The starfish, a destructive form, is not found to 
be a menace in North Carolina. 
An account of two parasites, believed to be trematodes and apparently not 
previously found in scallops, is given. One of these, rarely found, occurred on the 
gills as a sporocyst, containing redise which contained very numerous, peculiar 
cercarise. The other, found abundantly in the walls of the stomach, resembled the 
figure of a parasite found by Tennent in oysters at Beaufort and believed by him to 
