Winterkill and Summerkill 51 



Biologists and fish culturists liave tried to prevent the winterkill of 

 fishes in various ways, most of which have been ineflFectual. Some methods 

 explored for preventing winterkill of fishes are given below: 



1. Aeration of Water under Ice. Many attempts have been made to 

 blow air immediately under ice with pumps or blowers. This method is 

 largely ineffectual/ ^ particularly for waters of any size, because little 

 oxygen becomes dissolved in the water. 



Clear Ice 

 5 Inches Thick 



Cloudy Ice 

 15 Inches Thick 



1 Inch of Snow 



Over 



Clear Ice 



3 Inches Thick 



5 Inches of Snow 



Over 



Clear Ice 



3 Inches Thick 



Figure 3.1. Oxygen supply under winter ice depends upon the transmission 

 of sufficient light for photosynthesis of plankton algae and rooted submersed 

 plants. Light passes readily through clear ice and fairly well through cloudy 

 ice. However, an inch of snow blankets out 83 to 90 per cent of the light and 

 5 inches of snow, 97 to 99 per cent. Winterkill of fishes is more common 

 during winters when the snow on the ice persists for long periods than when 

 it is light or melts between storms. 



2. Aeration of Water above Ice. In 1935-36, the Michigan Institute for 

 Fisheries Research attempted experimental aeration by pumping water 

 from a lake and spraying it into the air where it fell to the ice and 

 returned through holes cut in the ice.^^ This caused improvement in 

 dissolved oxygen tension, but the effect was very localized, and tlie 

 oxygen disappeared within 28 hours. 



3. Pumping of Well Water. Well water at 50°F was run through 

 wire-mesh and over an inclined trough to increase the dissolved oxygen 



