REPORT OF COMMISSIONER OF FISH AND FISHERIES. XLIII 
fishes which resort to them. The methods of the fisheries are also 
largely dependent upon a knowledge of the habits of the useful species. 
The manner of conducting the survey of the fishing-grounds is ex- 
plained elsewhere. The information obtained is presented to the fish- 
ermen in the form of charts and descriptive text, the former enabling 
them to locate readily any desired spot, the latter describing its prin- 
cipal features. Until recently the discovery of fishing-grounds has 
chiefly been accidental, that is to say, not due to organized and well- 
directed efforts, and their resources have been ascertained only through 
their gradual development. The rapid increase of population neces- 
sitates, however, more active progress in this direction, and all the 
assistance that can be afforded by such comprehensive surveys as are 
now under way. The investigations of the steamer Albatross on the 
Pacific coast during the past year, described below, fully demonstrate 
the utility of such measures. 
THE DECREASE OF FOOD-FISHES. 
It was specifically for the study of this subject that the Fish Commis- 
sion was established in 1871, the results of its first inquiry determin- 
ing the later expansion of the work. Demanding in part the same 
method of treatment as the survey of the fishing-grounds, it requires a 
much more thorough execution and a closer attention to details. In 
the former instance the grounds were assumed to be in their normal or 
natural condition, but any marked decrease in productiveness is taken 
as an indication that the balance of life has in some way been disturbed. 
It then becomes essential to ascertain what changes have occurred, the 
causes producing them, and the measures necessary to restore the nat- 
ural conditions, finally carrying out those measures so far as practicable. 
Previous to the organization of the U. S. Fish Commission it was 
customary, in investigating matters of this kind, to rely mainly for evi- 
dence upon the testimony of persons dependent upon the fisheries for 
their support, and thereby prejudiced in one direction or another. We 
owe chiefly to Prof. Baird the inauguration of the natural method of 
inquiry now prevailing, not only in this country, but also to some extent 
abroad. The decrease of fishes may be due to natural causes, or to 
injudicious practices on the part of man. The existence of a decrease 
having been confirmed, its extent is generally difficult to determine, 
from the absence of concurrent observations, and while the causes may 
be evident on slight inspection, more often they are obscure. Among 
the human agencies instrumental in this respect are the large fixed 
appliances of capture along the shores, a too persistent fishing by other 
means, dams built across the streams, preventing the ascent and descent 
of fishes, and the pollution of waters by factory refuse. The natural 
caus'es are less well defined, such as the failure of the food supply, the 
ravages of predaceous fishes and other animals, changes in temperature 
