66 U. S. BUREAU OF FISHERIES 
North Carolina—Experimental studies of the growth, reproduction 
and survival of oysters at different tidal levels were continued at the 
Beaufort, N. C., Laboratory, under the direction of Dr. Herbert F. 
Prytherch. The purpose of this investigation is to obtain the essen- 
tial information required for improved cultivation of oysters on the 
extensive tidal flats of this region. Though conditions above low- 
water level are unusually favorable for erowth, the oysters produced 
in this zone are of inferior quality because of the overcrowding re- 
sulting from prolific natural reproduction. Biological studies show 
that oysters in this region have two heavy spawning and setting 
periods; in June and September. The late set usually completely 
covers the first set, which is attached to the shells and other cultch 
scattered over the tidal flats. The chief problem, therefore, in pro- 
ducing oysters of good marketable size and quality on these | areas, 1S 
to find a method of preventing “fouling” of cultch during the summer 
season. The principal lines of investigation undertaken were to de- 
termine the following: (1) The growth of seed and adult oysters at 
different tidal levels: (2) the intensity of oyster setting or other 
fouling of these oysters in relation to their vertical position ; (3) the 
possibilities of controlling fouling by shifting of oysters in special 
holding devices to favorable depths during the spawning season, and 
(4) the value of specially constructed salt-marsh ponds and canals 
for intensive cultivation of oysters where control of depth, current 
velocity, and other factors is possible. 
Four hundred oysters, 1 and 2 years of age, were attached to cement 
panels and studied w ith respect to growth i in weight, volume, length, 
and width in relation to their position above and below low-water 
level. Additional records were kept of a series of 180 oysters, which 
were studied individually during the previous year to determine the 
effect of orientation on growth. Three series of panels were placed 
under the main pier in Beaufort Harbor, using the same arrangements 
described for the experiments in 1938. Four other series of 100 Oys- 
ters each were placed at levels just above and below mean low-water 
mark in the improved marsh ponds and canals constructed adjacent 
to the laboratory. The unit panel employed in these experiments 
consisted of a reenforced slab of “Incor” cement, 343 X34 in., to 
which the oysters were fastened with a detachable cement. 
The general results of the entire series of gan may be briefly 
summarized as follows: (1) In this region the most rapid growing 
level for oysters is found in the tidal zone extending from approxi- 
mately 6 in. below low-water level to 12 in. above. (2) When seed 
oysters (vear-old size) are placed in this zone they will reach good 
marketable size in 2 years and show an increase in volume ranging 
from 750 to 1,200 percent, and in weight from 860 to over 1,000 per- 
cent. (8) The essential conditions required for attaining this growth 
are a good circulation of water, ample space for expansion, exposure 
to air for short periods, and protection from overcrowding and smoth- 
ering by other marine organisms. (4) The greatest increases in 
weight and size were obtained in the groups of seed oysters that were 
held in a vertical position with the hinge uppermost. Less than 10 
percent of these oysters died during the 2- -year period of experimen- 
tation. (5) The growth of oysters in North Carolina waters is most 
rapid during the Tate fall, winter, and early spring, and apparently 
