100 Conservation Department 



Summary and Conclusions 



In considering the results of the summer's work the various 

 branches of the subject will be summarized individually first and 

 later considered in terms of the objects of the survey. As stated 

 in the introduction, the problem can not be interpreted in terms 

 of chemistry, bacteriology, microplankton, macroplankton, or any 

 one of the subjects treated in the present report. They are all 

 so inter-related that any one must be discussed in the light of the 

 others and only from the combined results of all may we look for 

 the answers to the problems on the economy of the lake which 

 formed the object of the present investigation. 



Although many data of purely scientific value were obtained, in 

 order to avoid confusion these have been but briefly touched upon, 

 the bulk of the discussion being devoted to those findings appli- 

 cable to the immediate problems. Special subjects will be treated 

 in later publications. 



Physical Hydrography. — In cross section Lake Erie is on 

 either side bounded by sandy beaches or limestone cliffs sloping 

 gradually into coarse sand and finally beyond the influence of 

 land outwash into the basic smooth shale, honey-combed shale, or 

 faulted rock bottom, covered with almost no sediment of any sort 

 except for short distances off the mouths of the larger rivers. It 

 is this ''clean bottom" that such economically important species 

 as the whitefish select for spawning grounds and which has been 

 reported to contain in places heavy silt deposits. The central basin 

 contains a thick deposit of clay mud considered by some to be of 

 glacial origin, by others to be outwash from the land. In the 

 area included in the present survey this deposit is quite free from 

 industrial waste or sewage silt and is populated "by a rich bottom 

 fauna which offers an excellent source of food for fishes seeking 

 a deep-water habitat. 



Regarding the water mass, it has been said that Lake Erie in 

 storms is churned from top to bottom, the nets of the fishermen 

 torn, and in all probability great numbers of young fish and fish 

 food destroyed. Were this true one would expect to find in sum- 

 mer almost uniform temperatures from surface to bottom, but this 

 was not the case, at least during the period of the present investi- 

 gation. Descending from the surface the temperature was found 

 to decline gradually until in late August a level beyond the 

 influence of summer heating was encountered at about 20 meters. 

 Over a considerable area this cold layer of bottom water of 4 to 

 5 degrees Centigrade covered the floor of the basin. At times it 

 oscillated back and forth. One week it was found to have 

 advanced thirty miles toward Buffalo, and by the next cruise it 

 had retreated again even l)eyond its former position. The cause 

 of this movement has not been fully determined as yet, although 

 there appears to be a close correlation between the wind and the 

 movement of the water mass, the advance of the cold mass taking 

 place in the readjustment process of the lake after the termination 

 of the wind. 



^ 



