EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
205 
at one station (no. 6, fig. 1), 95 percent of dead shells were not infested by these pests. 
Oyster growers have not noticed an unusual increase in abundance of oyster enemies, 
and no evidence has been obtained which would indicate that such an outburst oc- 
curred at the time of the mortality in the winter of 1932-33. It is significant that in 
1933 the mortality affected chiefly the larger and older oysters of marketable size and 
in several instances was especially severe among the recently transplanted oysters. 
Undoubtedly, the practice of overcrowding the beds by planting from 700 to 900 
barrels of oysters per acre may be one of the contributing factors which aggravates the 
situation and in case of adverse environmental changes or the poor condition of the 
oysters, may materially increase their mortality. 
A more detailed survey of the oyster bottoms, made by R. O. Smith in 1934, failed 
to assign the mortality to any known disturbance of the natural conditions on oyster 
beds, as for instance, temperature, salinity, current, and invasion of enemies. It has 
been noticed that in general mortality has been higher on soft, muddy bottoms than 
on hard ground. At the time this survey was carried out, pollution was noticeable 
at the mouth of Bayou Grey where the surface of the water was covered with oil for 
a distance of 3 miles below the wells and there was some mortality on the oyster beds 
of this section. All shells were covered with a brownish-black coating of tarry con- 
sistency and the meats were unpalatable because of the strong oily flavor. Consider- 
able quantities of oil were held by mud, and oily patches appeared on the surface when 
the bottom w T as stirred. Light films of oil were observed also in the vicinity of the 
Lake Barre wells. In 1934 oysters on many beds throughout the region did not be- 
come fat until February or March, which points to a possible scarcity of food or to a 
disturbance in the functioning of the organs of feeding. 
The shallowness of the water throughout the oyster-producing region in Louisi- 
ana must be regarded as a factor which tends to magnify the action of any polluting 
substance. Due to stirring by wind, the water carries much suspended matter which 
may absorb the pollutant, transport it over wide areas, and deposit it on the bottoms 
far from the source of pollution. Observations in the polluted areas show that on 
account of the absorption by suspended clay particles, oil quickly disappears from the 
surface and after being deposited on the bottom, remains there for a long time. 
No information was obtained by the two surveys upon which to base an opinion 
as to the direct cause of mortality, but ample experimental evidence has been accumu- 
lated to show that the presence of crude oil in water produces conditions inimical to 
oysters. 
The first series of experiments designed to determine whether oysters could be 
killed by the presence of oil in the water or by direct contact with oil, gave negative 
results. Unfortunately because of the circumstances over which the investigators 
had no control, these experiments were carried out not in Louisiana, but in a different 
environment at Beaufort, N. C., with uncultivated oysters taken from oyster reefs. 
Samples of crude oil collected by the State Conservation Department from Louisiana 
oil wells were shipped to Beaufort and used throughout the experiments. It is quite 
possible that the results might have been different had Louisiana oysters been used. 
In a series of experiments lasting from 2 to 3 months, the mortality of oysters 
kept in running sea water under a surface layer of oil, and those kept in sea water 
that passed through oil was not greater than that in the controls. In the experi- 
ments carried out under similar but not identical conditions, Gowanlach (1934) 
observed considerable mortality among the oysters kept in oil-polluted water. The 
