468 
y 
DECREASE IN NUMBER OF FISH—ITS CAUSES AND REMEDIES. 
Apart from such well-known instances of the almost total disappearance 
of valuable food fishes where they were previously abundant, such as the disap- 
pearance of Salmon from Lake Ontario and of the Shad from the lower Ottawa, 
other cases of waters being “ fished out,” or of the yield of certain species being ~ 
on the decline are only too common. 
It has been impossible so far to collect evidence showing to what extent. 
waters within the Province previously rich have been depleted ; such Statistics. — 
however, are much required. : 
The causes of depletion are twofold: Such as are outside our control, and. q 
such as can by proper remedies be mitigated or avoided. oo 
Among the former are the changes in the conditions of life incident to the — 
opening up of the country for agricultural purposes, the removal of forests, the — 
reclaiming of swamps, the resulting changes in rainfall, or at least in the extent — 
to which surplus rainfall is held back by forest land and underbrush, and thus 
delivered only gradually and not in torrents through the streams. It is probably — 
to such changes, aided by other causes adverted to below, that we must attribute — 
the disappearance of Salmon from Lake Ontario. 4 
Not only do such changes directly affecting the surroundings of the fish react. — 
upon its abundance, but they also have an indirect effect through the food-supply.. — 
Brook Trout, as was before observed, have for their natural food the larve of 
various species of gnats and flies, the elimination of which from a cultivated. — 
country is looked on as one of the blessings of civilization. There is, however, — 
the reverse side to this advantage, the diminution of the favorable conditions for q 
insect life leading to a disturbance of the food-supply of the insectivovous fish, 
Various other obscure causes may interfere with the balance of life in any 
particular body of water, resulting in the wholesale destruction of one or more 
forms. 
These may be of the nature of epidemic diseases like the Salmon Saprolegnia. | 
due to the attack of a parasitic fungus, or in some way animal parasites, causing 
usually comparatively little injury, ay gain the upper hand and be the cause of 
widespread destruction. For example, Prof. A. C. Lawson brought tome some years _ 
ago specimens of an Argulus which he had taken from Whitefish dying wholesale 
in the Lake of the Woods, and shortly thereafter Mr. Washburn published in the 
American Naturalist an account of similar epidemics in inland lakes of Wis- 
consin. It has been suggested that the increase of the parasite is only possible. 
when the fish are already weakened by some other cause. 
Investigations into such cases are much required, and would be of much in- 
terest even although it might be impossible to obviate the cause when discovered. 
Other causes more immediately under our control are (1) illegitimate and 
destructive methods of fishing, including the capture of immature fish in immense 
quantities by the prodigal use of narrow-meshed nets and the use of illegitimate 
methods of fishing especially at the spawning time, when the habits of most fish 
expose them far more to destruction than at others ; (2) the destruction of spawn- 
ing and feeding grounds by sawdust or other mill-refuse, or by the decayed con- 
tents of gill-nets or offal from fishing boats; (3) the prevention of access to 
spawning grounds by obstacles placed in streams. 
