Lake Dynamics 



Lakes are usually more or less closed bodies of water, each forming 

 in a broad sense a small world of its own. Within their limits many 

 activities proceed automatically, making it possible for life to continue 

 indefinitely. Fishes represent the end of a long cycle in which the 

 chemical elements producing food pass from raw substances in the 

 water and on the lake bottoms into food for the higher forms of fish 

 life. 



Studies of northern lakes show that these lakes vary considerably in 

 the production of both food and fishes. Some lakes are poor in produc- 

 tivity, others are rich, and their differences are due to chemical fertility 

 limited by physical and biotic conditions. Owing to the variation in 

 chemical, physical, and biotic conditions from lake to lake, no two 

 lakes are identical in productivity. 



The most beautiful clear blue lakes are not necessarily the most 

 productive of fish life. In fact, the rock-bound lakes, with the clearest 

 of water, are among the least productive as far as pounds of fish per 

 acre are concerned. Although the fishes of these lakes may run larger 

 on the average than in other lakes, there are not as many of them. The 

 sizes and kinds of fishes are no measure of fish production in these lakes 

 of low fertility. 



The actual test of the productivity of a lake is the total number of 

 pounds of fish that can be produced, and not the size of individual 

 fishes. Fish size is a matter of individual competition, depending on 

 population density. 



In matters of production a lake may be considered in the same way 

 as any piece of land. Land raises products of various sorts — pasture, 

 forest, and grain — from which a crop of livestock or upland game 

 can be produced. Fishes may be considered a water crop, one that 

 takes from two to three years to mature. Consequently, a lake must 

 not only raise abundant fish food in the summer, but also provide suit- 

 able winter conditions for several years in succession in order to 

 mature a fish crop. In this way fish production differs from that of 

 upland game, a crop of which can be produced at the end of each 

 summer. 



Primarily fish production is based on the richness of a body of water, 

 just as the production or yield of a farmer's field is based on the fertility 

 of the soil. The factors causing fertility in a lake are the same as those 

 that make the soil productive. But just as a farmer's crops depend not 

 only on fertility but also on proper drainage and cultivation, so food 

 and fish production in a lake depend on proper temperature, proper 



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