156 
BULLETIN OF THE BUREAU OF FISHERIES 
Based on conditions existing on March 28, there was no evidence that the opera- 
tion of the sulphur wells had an injurious effect on oysters. 
On July 4, 1933, an oil well was out of control for 36 hours, during which time it 
was estimated that some 3,000 barrels of oil flowed into the lake. No appreciable 
quantity of oil was lost subsequently. One of the leases was reported to have been 
heavily covered with oil, and until November oysters were unmarketable on account 
of the oily flavor. 
On March 28, 1934, a combined sample of three-quarters bushel was tonged 
from these beds. Some of the oysters had a slight oily taste. The tonging caused 
patches of oil to appear on the surface of the water, indicating that some oil still was 
held by the mud. 
CONCLUSIONS 
The purpose of the survey described above was to supply a knowledge of the 
local and general factors in the environment of the oyster beds in Terrebonne Parish 
and adjacent territory which might have a bearing on the problem of pollution. 
The hydrographic data show that conditions of salinity, current, and tempera- 
ture were, at the time of the survey, suitable for growing oysters throughout the area 
covered, and it has not been possible to assign the mortality to any known disturb- 
ance of the natural conditions on the oyster beds. Bearing this in mind, special 
attention was given to several factors whose combined effect would tend to magnify 
the action of any polluting substance. Among these may be mentioned the shallow- 
ness of the water. Even moderate winds stir the bays from top to bottom so that 
the water carries much suspended matter. Any polluting substance is quickly and 
thoroughly mixed with the water and is adsorbed by suspended matter; it may be 
transported over wide areas and deposited on the bottom far from the source of 
pollution. 
In general, mortality has been higher on soft, muddy bottom than on hard 
ground or reefs. The significance of tins is not known, but there is no evidence that 
silting is directly responsible for the mortality observed. Probably because of the 
decomposition of the organic matter, a muddy bottom presents a less favorable habitat 
for oysters than that found on hard ground. 
In 1934, oysters on many of the beds throughout the region did not become fat 
until February or March, which points to a possible scarcity of food organisms during 
the fall and winter, or to a disturbance in the functioning of the oysters’ organs of 
feeding. Overcrowding would tend to aggravate this situation. The oystermen 
state that from 600 to 800 barrels, i. e., 1,500 to 2,000 bushels, are planted per acre. 
While this quantity may be supported so long as conditions remain normal and the 
food supply adequate, it is obvious that should mortality begin in such a concentra- 
tion it is likely to result in the loss of a considerable number of the oysters. 
No direct evidence was found that the mortality had been caused by any known 
natural enemies, although they may have an indirect effect by increasing calcium 
metabolism or competing for food, and, in some cases, possibly a direct injury by 
attack or the secretion of poisonous substances, for boring clams, sponges, and worms 
are abundant in parts of Lake Barre, Timbalier Bay, Terrebonne Bay, and Lake 
Pelto. The borer has not been included in the above consideration of enemies be- 
cause its habits, range, and destructiveness are well known, the damage done by it is 
fairly constant, and its depredations can be eliminated as a cause of the unusual 
mortality. 
