140 



On the other hand, to multiply iindnli/ by artificial measures any 

 species naturally abundant in such a lake, will have scarcely a less 

 disturbing influence than to diniiuish its numi)ers in the same ratio. 

 The relatively nice balance between the demand for food and 

 food supply which here naturally obtains, is such that an 

 extraordinary increase in a species must soon react 'o diminish 

 greatly its food resources — a fact which will then take effect on the 

 species itself, reducing it below its natural original level; and if 

 l/oth excessive capture and excessive multiplication 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 cultuript when young, it is evidently the food of 

 the young which will be first and most seriously affected by over- 

 production. Only a part of the adults, perhaps a small fraction, 

 will live a life of ordinary natural length, many being captured be- 

 fore they have attained even the average size ; but a far greater 

 number, perhaps nearly every one, must survive the earliest period 

 and iftust consequently draw most heavily upon the earliest food 

 resources of the species when these differ from those of the adult. 



The above considerations are brought forward here to show the 

 especial importance to us, of a study of the system of natural in- 

 teractions by which the animals of our great lakes affect each other, 

 if we would avoid the necessarily injurious consequences of our ovnti 

 interference with the natural order there obtaining, and above all to 

 show the extraordinary value of a knowledge of the food habits and 

 food capital of the young. They apply perhaps more forcibly to the 

 white-fish 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 distnictly different food when 

 young from that upon which it is dependent later. 



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

 million pounds of white-fish were taken in the Great Lakes m 1S79, 

 valued at over three quarters of a million of dollars, and represent- 

 ing nearly half the total sum derived from the lake fisheries of all 

 kinds. These fisheries 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 provided, 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 with what has been said above, it may not be difficult 

 to overdo the work of propagation. 



If the white-fish were to be multiplied indefinitely, without any 

 attention to the character or abundance of its food supply, it 

 would soon reach such a number tliat it must infringe upon its 

 own food capital, diminish the average number of the animals upon 



*C(>1USUS I'.llilrlill No. 'JOl. Sei.t. I.lSSl. 



