4 r. S. BUREAU OF FISHERIES, 



grounds is far creator than the danger of destruction. It has been 

 charged, but apparently not specifically estabhshed, 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 lie 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 fref|uently 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 noticeabl}^ 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 

 floatmg eggs and the delicate larvae 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 plants and animals on 

 which these larvae 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 municipa-l sewage 

 and similar sources; by destroying spawning grounds; by killing the 



