4 U. S&S. BUREAU OF FISHERIES. 
grounds is far greater than the danger of destruction. It has been 
charged, but apparently not specifically established, that fish in har- 
bors and the lower stretches of rivers have been killed by the dump- 
ing of oil from tankers. All of these vessels must clean out their 
tanks before they refill them and are prone to do so in harbor or as 
near there as may be. 
Well out at sea and in the larger bays the only source of consider- 
able oil pollution seems to le in the shipping, which, if it can not 
discharge in or near harbors, will do so at sea. Moreover, it seems 
clearly established that great oil films do form at sea. Huge patches 
have frequently been observed, and Collinge reports that sea birds 
have been found dead and dying by hundreds off the English coast, 
their feathers saturated with oil. Death of sea birds from the same 
cause is reported from our Pacific coast. 
Tar from freshly tarred roads may be washed bodily into gutters 
and thence into streams or other bodies of water. Apparently, how- 
ever, the greatest danger of direct action from tarred roads is from the 
fact that under the various influences at work—presumably heat, the 
mechanical action of vehicles, and soluble action of oils—poisonous 
substances are yielded to road washings for a great length of time. 
Various people in England, as recorded especially in the (London) 
Fishing Gazette, have described instances or experiments which indi- 
cate the continued poisonous action of tarred roads. Richmond 
found that although an undisturbed tarred surface became innocuous 
in three weeks, washings from material chipped from a road which 
had not been tarred for approximately one year were fatal to fish. 
Tarred road washings appear to be noticeably destructive of fish and, 
largely through the destruction of food organisms, of fisheries, chiefly 
in streams not larger than small rivers and ponds, particularly trout 
waters. In well-developed country so fortunate as to possess salmon 
streams, tarred roads doubtless constitute a menace to the salmon 
fishery. 
Oil from motor cars, etc., goes into small as well as large bodies of 
water and is of greatest volume at large towns. 
EFFECTS OF OIL POLLUTION. 
Oil remains in part as a surface film on the water, and is probably 
in part emulsified and distributed in intermediate strata, while the 
heavier fractions are deposited on the bottom, where they persist 
for a long time. All parts are washed ashore to be deposited on the 
beaches and vegetation between tide marks. 
This pollution may affect the fisheries in various ways: By actu- 
ally killing or repelling the fish when they approach the shores in 
their migrations, at the only time when they can be caught; by sick- 
ening or killing bottom-dwelling species such as oysters; by killing 
floating eggs and the delicate larve which, swimming at or near the 
surface, are suffocated by the deposit of an impervious film on the 
gill surface; by destroying the minute surface mane and animals on 
which these larve and some of the adult fishes subsist; by diminish- 
ing the aeration of the water at the surface and thereby aggravating 
the deoxidizing effects of organic pollutions from municipal sewage 
and similar sources; by destroying spawning grounds; by killing the 
