AN ECOLOGICAL RECONNOISSANCE OF THE FISHES OF 

 DOUGLAS LAKE, CHEBOYGAN COUNTY, MICHIGAN, 

 IN MIDSUMMER." 



By JACOB REIGHARD 

 Professor of Zoology, University of Michigan. 



INTRODUCTION. 



During the summers of 1909, 191 1 , and 1912 I was in charge of the biological station 

 of the University of Michigan, situated on Douglas Lake. The little time that remained 

 to me after my routine duties was given to collection of data bearing on the ecology 

 of the fishes of the lake. It was my hope after a considerable number of years to reach 

 general principles by the analysis of data thus collected. It is unlikely that I shall 

 continue the work. It seems, then, worth while to put on record such facts as I have. 

 They are few, and the inferences that may be drawn from them are tentative; yet 

 they may furnish a starting point for some one else or suggest a method. The records 

 of 1912 were made under my direction by an assistant, Mr. M. E. Houck. 



Douglas Lake — Turtle Lake on many older maps — (fig. i), lies at about latitude 

 46° 30' N., in the Southern Peninsula of Michigan, at an altitude of 712 feet above 

 sea level. Its northern shore is some 15 miles in a direct line from the Straits of 

 Mackinac. Its greatest length from east to west is 3K miles, its greatest width 2>^ 

 miles. The lake has somewhat the fonn of a fish, the flukes of whose tail form North 

 and South Fishtail Bays at its eastern end. The total area of the lake, exclusive of 

 Fairy Island, is about 5.1 square miles; its shore line, including that of Fairy Island, 

 measures 14 miles. The shores are nearly everywhere a mixed sand of granitic origin. 

 The water deepens gradually over a terrace or shoal until it is 3 to 6 feet deep. The 

 terrace varies in width from a few yards to a hundred or more. The bottom then 

 drops rapidly, in most places into deeper water, forming the "slope" or margin, which 

 is as steep as loose sand can lie. The slope is that part of the bottom on which vege- 

 tation ordinarily grows. It extends to the lakeward limit of vegetation, usually at 

 a depth of not more than 25 feet. The depth of water at the lakeward limit of vege- 

 tation in Douglas Lake is unknown. The deeper water beyond the slope has a depth 

 of 82 feet over a limited area near the southern end of South Fishtail Bay, and a depth 

 of 89 feet at another point. The deeper water does not reach 80 feet over most of the 

 lake and is not continuous but is interrupted by bars and shoals. Pending the comple- 

 tion of a hydrographic map, details are not available. 



A white disk lowered into the water on August 12, 191 3, disappeared at a depth 

 of 12.5 feet. This indicates that the lake is not rich in plankton, but no plankton 



<^ Contributions from the Zoological Laboratory of the University of Michigan, no. 143. 



219 / 



