9] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 9 



Secchi's disc. The fish have been collected from practically every lake, 

 and from all rivers and streams. In collecting fish, gill nets were used. For 

 the smaller species and the young of the larger, minnow nets of various 

 lengths were drawn where opportunity afforded. When physical conditions 

 rendered this method impossible and in all streams where a current made 

 it practicable, the glass minnow trap was used with excellent results. 

 It is impossible to state exactly how many collections were made as in the 

 early stages of the investigation the only records kept concerned the 

 presence or absence of species; however, beginning with 1918 the following 

 number of collections are recorded: 1918 — 216; 1919 — none, due to the 

 presence of the writer in France; 1920—547; 1921—520; 1922—738; 

 1923—1,264; a total of 3,285. Certainly well over 4,000 are represented. 

 Further information has been obtained by examining the catches of 

 commercial fishermen who nearly every fall seine in the neighborhood. 

 By this means many data have been accumulated regarding the relative 

 abundance of species, together with information dealing with size and 

 growth otherwise unobtainable. The investigations have been, perforce, 

 largely carried on during the summer months, but from two to three weeks 

 have been spent in the region every winter, during which time the condition 

 of the lakes and the fish in winter have been investigated. All identifications 

 have been made by the writer and in every case this has been checked by 

 an expert ichthyologist. 



In presenting this paper the writer wishes to express his appreciation 

 to several gentlemen whose kindly encouragement and ever-ready advice 

 have made the pursuance of the problem a real pleasure: to Dr. A. S. 

 Pearse, under whose guidance the problem was originally begun; to 

 Dr. Bashford Dean and to Dr. T. L. Hankinson, who have checked up 

 identifications of the fishes involved; to Dr. H. B. Ward whose suggestions 

 and criticisms have always been freely given, and to Dr. V. E. Shelford, at 

 whose suggestion several hitherto uninvestigated angles of the problem 

 were undertaken and under whose guidance the innumerable loose ends 

 accumulated during something like twelve years of investigation were 

 drawn together and synthesized. To these the writer finds it a rare privilege 

 to express his sincere thanks. 



REGION UNDER DISCUSSION 



Waukesha county, Wisconsin, with an area of 560 square miles (Fig. 8), 

 lies in the second tier of southern counties of the state, with its eastern 

 boundary about twenty miles west of Lake Michigan, Milwaukee county 

 intervening. Of this area, the northwestern quarter, comprising some 170 

 square miles, is the center of the investigations considered in this report, 

 and is the so-called "Oconomowoc-Waukesha lake district." This region 

 extends from the Ashippun river on the north 14 miles south to Hunter's 



