FISHES OF DOUGLAS LAKE, MICHIGAN. 



245 



The cross in the table indicates that the species avails itself of the factor indicated; 

 the zero indicates that it does not, or, in the case of the column headed "Protection," 

 that it does not need to. Adult Am^iurus, Ambloplilcs, and Micropterus are larger 

 than the perch which exist outside the vegetation. They must be held to it by some 

 other factor than the need of protection. This may be food or some factor not included 

 in our table. Since some of the species may obtain their food outside the vegetation, 

 the data in our table indicate that no one of the factors considered necessitates the occurrence 

 together of the species which make up the vegetation community. 



Table IX. — Showing the Relation op the Species op Fishes Included in the Vegetation 

 Community to the Three Factors op Food, Protection, and Breeding Afforded by the 

 Vegetation. 



THE DEEP-WATER COMMUNITY. 



In the deeper water near the bottom, down to about 45 feet, the following forms 

 have been taken in midsummer: 



Catostomus commersonii (common sucker), from 7 to 12 inches long, approximately. 



Esox lucius (pike), between 12 and 30 inches long. 



Micropkrus dolomieu (small-mouthed black bass), between 12 and 16 inches long. 



Perca flavescens (yellow perch), 8X inches long. 



Lota maculosa (burbot), large. 



All these fishes wander far from the vegetation. The small-mouthed black bass 

 feeds chiefly on crayfish. Presumably the larger pike prey on the other fishes of the 

 community, but our records do not show that any pike had eaten fishes more than 4K 

 inches long. These were perch of a size found only among vegetation and were doubt- 

 less taken by the pike at its borders. It seems probable that the five fishes of this com- 

 munity are protected from one another in part by their size, for the individuals of each 

 kind are usually too large to be eaten by the others except by the largest pike or burbot. 

 The perch remain in the aquatic vegetation until they are about 6 inches long and large 

 enough to enter the deep-water community. 



The fishes of the deep-water community, except possibly the burbot, are much 

 about the borders of the patches of vegetation and more or less within these patches. 

 Here the pike (no. i, 2, 3, 5, 6, 15, 16, table iii) obtains the smaller perch and probably 

 the other fishes of the plant zone. To a lesser degree, the small-mouthed black bass 

 may obtain fish from the same source; at any rate it is commonly taken on the lake- 

 ward margin of the plant zone on hooks baited with shiners or spot-tailed minnows. 

 The sucker is also known to enter the patches of aquatic plants. The characteristic 

 feature of the deep-water community is then that its members occur near the bottom in 

 deeper water outside the patches of aquatic plants, not that they may not also occur 



