Biological Survey — Erie-Niagara Watershed 69 



Its Horizontal Distribution. — The present survey began the 

 middle of June and lasted until the middle of September, and 

 hence the distribution here given is for the summer season only. 

 In the horizontal distribution of the plankton Crustacea 3 zones 

 may be distinguished with considerable accuracy. Of course, it is 

 understood that along the margins where two of these zones come 

 together there is more or less overlapping of species, and migra- 

 tion back and forth from one zone into the other. But in general 

 the limits seem fairly well drawn and each zone has its own 

 characteristic species as well as those common to other zones. 



The marginal zone: This includes the shallow Avater along the 

 shores of the lake up to a meter in depth and also in the mouths of 

 the tributary creeks. This zone can be most conveniently examined 

 by wading from the shore and by washing out the sand and mud 

 in a few inches of water. In this zone also may be properly in- 

 cluded the small ponds adjacent to the lake and others at a greater 

 or less distance from the lake but draining into the tributary creeks 

 of the latter. In proof of this may be mentioned the fact that 

 practically every species of crustacean found in these ponds, in- 

 cluding even 3 Harpactids, have been identified in the stomach 

 contents of fishes seined near the mouths of the creeks or along 

 the shores of the lake. At the depth of a meter the plankton begins 

 to change rapidly into that of the second zone, and here many 

 species are common to both zones. Among these a quite unexpected 

 discovery was the presence of Leptodora in considerable abund- 

 ance ; this curious cladoceran can even be washed out of flocculent 

 mud in two or three inches of water among the water plants. ^ Of 

 Crustacea peculiar to this zone and not found in deeper portions 

 of the lake were 2 copepods and 8 cladocerans. 



Owing to unavoidable circumstances this zone received but little 

 attention during the present season, but the results obtained were 

 very suggestive. The number of genera and species of Crustacea 

 far surpasses that of both the other zones combined. And this 

 fact assumes considerable economic importance when we remember 

 that the newly hatched fry of many lake fish congregate in shallow 

 water close to the shore and in the mouths of the various creeks. 

 These first few weeks of the fish's life are a critical period of its 

 existence during which it needs plenty of good food. That each 

 of these Crustacea contribute toward that end is abundantly proved 

 by finding them in the stomachs of young fish. Every species 

 of copepod and cladoceran is one more possible addition to the 

 daily menu of some fish, and although it may not be as large and 

 toothsome as some of the others, it may yet contribute materially 

 to the fish's nourishment. On the basis of such consideration this 

 zone may well lay claim to a more careful and extended examina- 

 tion another season. 



The littoral zone: This includes the shallow water from 1 to 10 

 meters in depth and of necessity shows more or less overlapping 

 in two directions, toward the shore and toward the deeper por- 

 tions of the lake. The examination of this zone can be best con- 

 ducted from the lake itself, and with a smaller boat that can 

 enter quite shallow water. During the present survey this zone was 



