Management of Waters for Fish Production 



The lakes of the North Central States have long been famous for 

 their game fishing. However, with the recent increase in population 

 and the increased use of automobiles and even airplanes, the fishing 

 pressure, or amount of fishing, has steadily increased, and in conse- 

 quence good fishing is disappearing from many popular lakes. In re- 

 cent years preliminary studies have been made to determine ways to 

 maintain good fishing, and our knowledge of the requirements of fishes 

 and the management of lakes and streams is increasing. 



Lake management is the control of a body of water and its contents 

 in such a way as to produce a sustained yield of the fishes best suited 

 to the conditions of the lake. By indicating the amount of fish that can 

 be removed without disturbing the conditions necessary for maximum 

 production, lake management seeks to prevent the damage done by 

 intensive fishing. It involves the improvement of the environment for 

 fish life and the maintenance of a balance of size ratio in the population. 

 The management of all waters should be based on information ob- 

 tained by surveys of all conditions necessary to life. Lake and stream 

 surveys are not cures for any troubles, but they are the chief means 

 of diagnosing fishing problems. 



The surveys determine the productivity and carrying capacity* in 

 terms of the elements of fertility and the resulting food and fishes. 

 Such surveys have been initiated and developed within the last fifteen 

 years, largely within the northern states of New York, Michigan. Ohio, 

 Indiana, Ilhnois, Wisconsin, and Minnesota. 



A complete survey includes basic mapping of the lakes and a census 

 of bottom fauna, plankton, and fishes. The chemical nature of the water, 

 especially the carbonate and in some cases the phosphate, nitrate, and 

 sulphate content, is determined. The temperatures at different depths 

 are determined. The spawning beds and the weed areas are measured. 

 The results constitute an inventory of all the conditions for fish life. 



The chief result of lake surveys is the determination and classification 

 of the types of lakes suitable for various game fishes. Each lake should 

 be managed to produce the kind of fishes for which it is naturally 

 adapted. It is not practical, for example, to attempt to manage a 

 walleye lake for lake trout, or a bass lake for walleyes. Minnesota lakes 

 can be divided into soft- water and hard-water lakes, and also into cold- 

 water and warm-water lakes. The proper combination of hardness and 

 temperature determines whether a lake can support cold- or warm- 



*The carrying capacity of a body of water is the amount of any or all forms of life 

 supported at a given time. The term is usually used in fish management instead of 

 "annual or total yield," which is virtually impossible to measure. 



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