242 BUI^LETIN OF THE BUREAU OK FISHERIES. 



THE STONY-SHOAL COMMUNITY. 



It has been pointed out that the presence of stones adds to the community of 

 young fishes found on the stony shoals the blunt-nosed minnow. This form when 

 breeding may be regarded as a member of the stony-shoal community. This commu- 

 nity would then consist of three fishes which lay their eggs beneath stones — the blunt- 

 nosed minnow, the miller's thumb, and the johnny darter. The miller's thumb makes 

 excavations beneath stones and attaches its eggs in a mass to their lower sides (Han- 

 kinson, 1908). This has not been observed in Douglas Lake, but the fish themselves 

 have been found beneath stones on the stony shoals and nowhere else. The johnny 

 darter also lays its eggs on the lower sides of stones. It has rarely been found in Douglas 

 Lake or elsewhere than on stony shoals or adjacent to them. 



With the three fishes which form this community is found a small crayfish, Cawbarw^ 

 propmquus Girard. It forms burrows beneath stones, and these may be recognized by 

 the little piles of fresh sand at their mouths. 



The stony-shoal community, unlike that of young fishes, is composed of both 

 young fish and adults and is probably permanent. What happens to its members 

 when the shoals are ice covered we do not know. 



The food of the young johnny darter is known to consist of Entomostraca, while 

 that of the adult is chiefly midge larvae with an admixture of Entomostraca. (Heim- 

 burger, 1913.) The blunt-nosed minnow takes a varied food, which, according to 

 Hankinson (1908), consists chiefly of small organisms taken from the bottom, from 

 water plants, and from the water. It appears that midges in various stages of develop- 

 ment formed the chief food of this species in April and May. Besides midges, filamen- 

 tous algae, desmids, entomostracans, and in one case beetles, were found in the stomach. 

 The food of the miller's thumb in Illinois was found to contain about 25 per cent of 

 small fishes, 40 per cent aquatic larvae, and the rest mostly Crustacea {Asellus). 

 (Forbes and Richardson, 1908.) In Douglas Lake the blunt-nosed minnow and the 

 johnny darter take similar food and find it in the same place, yet the blunt-nosed min- 

 now has a somewhat larger choice, and the two forms are not altogether in competition. 

 The miller's thumb presumably takes its supply of fish from among the blunt-nosed 

 minnows and johnny darters, while the crayfish afford it Crustacea. 



THE VEGETATION COMMUNITY. 



The vegetation community includes the following forms: 



Afnciurus nebulosus, bullhead. 

 Nolropis hudsonius, spot-tailed minnow. 

 Notropis cornuius, common shiner. 

 Percopsis gutlatus, trout perch. 

 Ambloplites rupestris, rock bass. 

 Lepomis pallidus, bluegill. 

 Eupomotis gibbosus, common sunfish. 

 Micropterus salmoides, large-mouthed black bass. 

 Perca flavescens , yellow perch, 4 to 6 inches long. 

 Percina caprodes, log perch. 



Of these 10 species 8 have been found only in the vegetation, although, as pointed out 

 elsewhere, some of them enter other habitats at the breeding season or when young. The 



