American Fisheries Soeiety. 29 



water gradually increases in thickness during the summer and 

 early autumn — in late August and September. 



Chairman Whitaker: To the bottom? 



Professor Birge: Towards the bottom. In October you may 

 say in a general way the Crustacea and the plants are distributed 

 about uniformly through the whole depth of the water. I can 

 illustrate the distribution of the animalcules on certain dates 

 when they were accurately determined. For instance, figuring 

 the Crustacea on this particular day, August 12, 1896, below 10 

 meters there were in a column of water a meter in area, and 8 

 meters in depth, 5,500 Crustacea. In the lower part of the warm 

 water, in a cubic meter of warm water, there were 24,000. There 

 were four times as many Crustacea in the bottom meter of the 

 warm water as there were in the whole 8 meters that lay below. 

 In the next meter above there were 66,000 Crustacea, so that the 

 difference is simply enormous. On another date there were 

 found 3,600 Crustacea, from 11 to 18 meters, while in the next 

 meter above (10 to 11) there were 20,000, and in the meter 

 above, 43,000 Crustacea in a single cul)ic meter. So that while 

 in the 7 meters below the warm water there were only about 500 

 Crustacea per cubic meter, in a single cubic meter above there 

 were 20,000, and in the next above that twice as many more, 

 over 40,000. 



Now you can see the bearing of this. There arc some insect 

 larvae, not very numerous, that go right up and down through 

 this stratum, and there are mollusks, Cyclas, that we find in the 

 nnid at the bottom. But you can see at once that the supply of 

 food for fish in this bottom water under this condition of things 

 must be extraordinarily small. Now, I imagine that one thing 

 which all fishermen tell us, that the white fish in Lake Mcndota 

 congregate during the summer in the region of the springs, is 

 possibly true (although I have never lieen able to locate those 

 springs). It seems reasonably clear that if they spread themselves 

 around the lake they must get short picking in the matter of food, 

 because very little food is there. And so, again, it is possible that 

 this scarcity of food is one of the causes which brings about the 

 death in our region of a considerable number of white fish to- 

 wards the latter part of the summer. 



The other point of practical importance is this: Tliis accumu- 

 lation of decomposing matter in the lower part of the lake may 

 not be without a direct efifect on the fish life that is present. Just 

 about thirteen years ago, in 1884, we had in Lake Mendota a 



