162 Thirty-fifth Annual Meeting 
Mr. Titcomb: I want to ask Dr. Birge if he has in any way 
observed the movement of fish with reference to the changes in 
temperature of the depths. ‘Take for instance, the lake trout 
which inhabit the very deep waters in August, and in June, we 
will say, is in four feet of water or near the surface. 
Dr. Birge: I have not been able to follow the fish. As yet 
we have not had money enough to chase both gas and fish at the 
same time. 
Mr. Titcomb: One more question: This is a subject that 
interests me a good deal because I have for a long time had a 
great desire to locate a hatchery with a lake as a water supply for 
the propagation of salmon and trout, and have an unlimited sup- 
ply of water from the lake. Now almost every trout and salmon 
lake that I know of gets too hot on the surface, and it would be 
practically impossible to take surface water from even a trout 
lake of large area and supply a hatchery to rear fish in the sum- 
mer time. My idea was to regulate the temperature, possibly 
varying it to suit conditions by taking it at varying depths. I 
am surprised to see there is so little variation in the first 8 me- 
ters, because I have tested lakes where there was much more vari- 
ation in less depth, but this brings in the subject in such way that 
when we consider a water supply of that sort we must: go into 
it more fully than f had thought, and consider the supply of oxy- 
gen and action of gases, as well as of temperatures. 
Dr. Birge: The depth to which the warmth of summer will 
extend is primarily a function of the size of the lake. Of course 
granting that the lakes are in the same general region. A lake 
further north will not be as warm as one further south; but in 
the case of lakes within 50 miles of each other, the larger the 
lake the thicker the warm layer will become, as you will see, 
when you understand it depends primarily on the action of the 
wind. 
You will notice in the diagram of Lake Mendota the cold 
laver starts at 8 meters and goes down to the bottom. In Elk- 
hart Lake, which is only 110 acres in extent, the warm layer 
s about 5 or 6 meters in thickness; and in Beasley Lake the warm 
layer is only 4 meters in thickness. The warm layer in August 
in this lake is about as thin as you can find it in anything you 
