7] STUDY OF SOUTHERN WISCONSIN FISHES— CAHN 



GENERAL ECOLOGICAL CONSIDERATIONS 



INTRODUCTION 



The first section of this paper is intended to serve as a general intro- 

 duction to a series of ecological studies made upon the fishes of southern 

 Wisconsin. At the present time the writer has a record of ninety species of 

 fishes from within the boundaries of Waukesha county alone, and upon 

 these species a considerable number of ecological studies have been com- 

 pleted. Two of these studies are herewith presented, one on the brook 

 silversides (Labidesthes sicculus), the other on the cisco {Leucichthys artedi). 

 These have been selected as the first studies presented for three reasons. 

 In the first place, the fishes themselves differ greatly, one being a minnow, 

 the other a valuable game and food fish; secondly, the fishes occupy posi- 

 tions in the lake as widely divergent as possible, the silversides being a 

 surface species, the cisco an inhabitant of the deepest water; and lastly 

 because the study of the cisco brought out a series of ecological problems 

 of approximately ordinary complexity, while the study of the silversides 

 presented a series of problems for solution that is far more complicated than 

 has been encountered in any of the other investigations so far undertaken. 

 The writer feels, therefore, that, taken together, they give a comprehensive 

 idea of the type of problems encountered in a series of ecological studies 

 dealing with the fishes inhabiting our inland lakes. 



It is altogether probable that no lakes in the United States have been 

 more carefully or more extensively studied than those of southern Wiscon- 

 sin, from the point of view of hydrography, morphometry, chemistry and 

 yearly cycle. The pioneer limnological studies of Birge and Juday have 

 yielded a mass of information relating to the behavior and physical and 

 chemical status of these bodies of water which is second to none in the 

 entire country, the closest approach being the "finger lakes" of north- 

 central New York, which is also due largely to the work of these investi- 

 gators. Their most extensive studies have been made on Lake Mendota, 

 at Madison, Wisconsin, together with Monona and other lakes connected 

 by the Yahara river to the Rock river, but their surveys have encompassed 

 as well the lakes farther east, lying in Waukesha county. As a result of 

 these researches one has very excellent hydrographic and morphometric 

 data invaluable for the further study of aquatic biota of this region. The 

 yearly behavior of the lakes is well known; the progress through the seasons 

 of the thermocline and the associated phenomena have been comprehen- 



