THE GERMAN CARP IN THE UNITED STATES. 598 
clear; and it has several rather important economical bearings besides 
the mere fact that it usually accompanies or is accompanied by the 
uprooting of the aquatic vegetation. The constant roiliness of a body 
of water that has theretofore been clear must be an important ecological 
factor in determining the quantity and character of both the vegetable 
and, at least secondarily, the animal life inhabiting it. This will 
readily be appreciated when we consider that it decreases the amount 
of light that would reach to any given depth, thus depriving plants at 
that depth of at least a part of one of the most important conditions 
for their growth, while in the second place the settling of the sedi- 
ment upon the stems and leaves of the plants acts asa mechanical hin- 
drance to the ordinary processes of respiration. Where the balance 
is once upset in this way in a body of water where things have become 
adjusted to a certain set of conditions, it is difficult to predict just 
what.results will follow in the readjustment to new conditions; but it 
is safe to assert that practically all the living organisms in the water 
will be influenced to some extent. Even if the vegetation were not 
uprooted by the stirring up of the mud of the bottom, it is probable 
that its abundance would be greatly reduced by the constant roiliness 
of the water. This would in all likelihood affect the plankton or free- 
swimming organisms as well, and thus greatly reduce the natural 
food supply of the fish. In the large bodies of water these conditions 
are ameliorated to a large extent, since by the movement of the fish 
from place to place they are often absent from a given locality for 
considerable periods, thus giving the sediment an opportunity to settle 
and allowing the water to become clear; and even in smaller areas the 
fish are not feeding all the time. But it must be admitted that where 
there are a comparatively large number of carp in a pond the water 
is kept in an almost constant state of roiliness. In the case of run- 
ning waters there is a further tendency to impoverishment in the 
carrying away of the rich mud while it is held in suspension in the 
water. There has been no direct evidence collected, so far as I am 
aware, to show to what extent this may be effective. It has even been 
claimed by some that dikes and dams are weakened in this way, by 
the destroying of the vegetation that held the mud in place, and the 
loosening of the mud itself. 
The roiliness of the water caused by carp in supply reservoirs 
has, in a number of instances, proved to be a serious problem, and is 
one which has to be met with promptness. The only practicable rem- 
edy is the removal of the fish. In some places this can be done with 
comparative ease by persistent seining; but more often, especially in 
large reservoirs which present a diversity of conditions, this method 
is not feasible. In some cases it may even be necessary, where the 
disturbance is very great, to withdraw the water and drain the 
reservoir for the purpose of getting rid of the carp. An interest- 
F. C. 1904—38 
