108 



ILLINOIS BIOLOGICAL MONOGRAPHS 



[108 



are found in the stomach. A cisco with an empty stomach is the greatest 

 rarity I recall in the fish life of the region under consideration, rarer even 

 than young of the species, for I have yet to find a single empty stomach 

 in a healthy fish. 



That the species is gregarious is borne out by the fact that during the 

 winter when the fish are sometimes seen at the surface, neither I nor any 

 of the hundreds of cisco fishers with whom I have spoken have evern seen 

 a lone cisco. When traveling near the surface at times the schools are 

 seen to number several hundred individuals; the smaller schools are 

 composed of from twenty to sixty fish. While these schools are to a certain 

 extent composed of fish of varying sizes, the large and small fish do not 

 mingle to any great degree, there being a marked uniformity of size in the 

 component individuals in each school. That these facts hold also for the 

 summer months is indicated by the gill net catches. Often I have missed 

 a catch entirely, but the smallest number of fish I ever caught is 5; the 

 largest is 33, in a fifty foot net, four feet deep with one and one half inch 

 mesh. Surely this shows unmistakable gregariousness. 



During the summer when the thermocline has driven the fish from the 

 deepest water, the fish travel in schools, parallelling exactly the contours 

 of the sand bars. The interesting fact about this travel is that it has a 

 definite direction: the fish travel west along the north shore of Oconomo- 

 woc lake, south along the west shore, east along the south shore and north 

 along the east end of the lake. This has been demonstrated by noting the 

 direction in which the fish are found in the gill nets along the different 

 shores. This is brought out in table 27. 



Table 27 



THE DIRECTION OF TRAVEL OF THE CISCO ALONG THE SHORES OF 

 OCONOMOWOC LAKE IN SUMMER 



These figures are the result of a series of catches during the summers of 

 1921 and 1922 and represent the total catch of 20 nets set in each direction 

 along the shore. The low figures for the east and west shores are explainable 



