42 ILLINOIS ACADEMY OF SCIENCE. 



by the United States Fish Commission and the United States 

 Census Bureau for 1894, 1899 and 1908. The second of these 

 census years came just before the opening of the Chicago Drain- 

 age Canal in 1900, and the last one eight years after that revolu- 

 tionary event, and nine years after the introduction of the Euro- 

 pean carp into the public waters of this State. The two occur- 

 rences of critical importance within the period covered by these 

 reports are thus the opening of the drainage canal and an enor- 

 mous increase in the numbers of carp. 



The drainage canal, by increasing the average depth of the Illi- 

 nois River between two and a half and three feet, and greatly 

 enlarging the area and lengthening the period of overflow, has 

 greatly extended the lateral range of the fishes of the river, espe- 

 cially in its middle course, enlarging at the same time their breed- 

 ing grounds and feeding grounds, and bringing into the stream 

 a tremendous load of sewage from Chicago and its suburbs. The 

 first effect of such an enlargement of the aquatic area must be to 

 scatter the normal fish population more widely and make it less 

 accessible to the fisherman. On the other hand, the enlargement 

 of their breeding and feeding grounds doubtless tends to an in- 

 crease in the numbers of fishes by the better provision made for 

 the survival of the young ; while the final eft'ect of sewage con- 

 tamination upon the inhabitants of the stream will turn upon the 

 manner in which these organic contributions are gradually 

 worked up. through the ascending series of the plants and animals 

 of the water, the margin, and the bottom, to bring them within 

 the reach of fishes in some form of life available for their food. 



The most interesting result I have obtained from an analysis 

 and comparison of the three census reports referred to is an indi- 

 cation that the numbers of our native bottom-feeding fishes are 

 being gradually diminished as an indirect consequence of the rapid 

 and enormous multiplication of the introduced carp. This fish 

 has now become so abundant, and commercially so important, that 

 it is the main object of our commercial fisheries. The yield of the 

 Illinois River, for example, was $412,000 worth of carp in 1908, 

 while the value of all the other fishes taken from the stream that 

 year was only $309,000. In 1894 the carp yielded, in Illinois, 860,- 

 000 pounds ; five years later, nearly 10 million pounds ; and nine 

 years later still, 21,642,000 pounds — the value of this Illinois yield 

 increasing in this period 27^ times, or from $21,000 to $574,000. 

 The native coarse fish, on the other hand, which, like the carp, 

 search the bottom of the stream for their food, yielded approxi- 



