468 



DECREASE IN NUMBER OP 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 CKtent 

 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 

 such as can, by proper remedies be mitigated or avoided. 



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, 



Not only do such changes directly aflTecting 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 larvae 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 th3 favorable conditions for 

 insect life leading to a distui-bance of the food -supply of the insectivo'"ous 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, may gain the upper hand and be the cause of 

 widespread destruction. For example, Prof. A. C. Lawson brought to me 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. Warshburn 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 oflfal from fishing boats; (3) the prevention of access to 

 spawning grounds by obstacles placed in streams. 



