772 EEPOKT OF COMMISSIONER OF FISH AND FISHERIES. [2] 



slowly than if it occurred to a pond or river species, accustomed, as 

 most of the latter are, to fill up rapidly enormous gaps in their numbers. 



On the other hand, to multiply unduly by artificial measures any spe- 

 cies naturally abundant in such a lake will have scarcely a less dis- 

 turbing influence than to diminish its numbers in the same ratio. The 

 relatively nice balance between the demand for food and food supj)ly 

 which here naturally obtains is such that an extraordinary increase in 

 a species must soon react to diminish greatly its food resources — a fact 

 which will then take effect on the species itself, reducing it below its nat- 

 ural original level; and if both excessive capture and excessive multi- 

 plication go on side by side we shall have this result finally aggravated 

 to an extreme degree. 



As fishes are caught before the end of their natural lives, but planted 

 by the fish-culturist when young, it is evidently the food of the young 

 wliich will be first and most seriously affected by overproduction. 

 Only a part of the adults, perhaps a small fraction, will live a life of 

 ordinary natural length, many being captured before they have attained 

 even the average size; but a far greater number, perhaps nearly every 

 one, must survive the earliest period and must consequently draw most 

 heavily upon the earliest food resources of the species when these dif- 

 fer from those of the adult. 



The above considerations are brought forward here to show the espe- 

 cial importance to us of a study of the system of natural interactions 

 by which the animals of our great lakes affect each other, if we would 

 avoid the necessarily injurious consequences of our own interference 

 with the natural order there obtaining, and above all to show the extra- 

 ordinary value of a knowledge of the food habits and food capital of 

 the young. They apply perhaps more forcibly to the whitefish than to 

 any other species in the lakes ; because this is for several reasons the 

 most important purely fresh-water fish of the Great Lake region, and 

 proves to have a distinctly different food when young from that upon 

 which it is dependent later. 



According to the recent census report,* more than twenty-one mill- 

 ion pounds of whitefish were taken in the Great Lakes in 1879, valued 

 at over three-quarters of a million dollars, and representing nearly half 

 the total sum derived from the lake fisheries of all kinds. These fish- 

 eries employ over five thousand men, and a fixed capital of one million 

 three hundred and forty-six thousand dollars. When we reflect that 

 this enormous drain upon the number of the species is necessarily, to a 

 - considerable extent, an addition to the natural tax levied upon it by its 

 enemies other than man, we see that there must be an artificial supply 

 l)rovided, or the fisheries will gradually fail. 



The importance of the knowledge of the food of so valuable a species 

 needs "no demonstration, especially when we consider that, consistently 



'Census Bulletin No, 261, September 1, 1881. 



