102 American Fisheries Society 



prohibited on the breeding grounds during a period long 

 enough to adequately cover all fluctuations of the breed- 

 ing season. 



The presence of fishermen on the lake during the 

 breeding season in greater numbers than under the exist- 

 ing system, should serve to protect the breeding grounds, 

 for they would watch one another. Each would tend to 

 see that others did not encroach on the prohibited areas. 



4. Construction of Breeding Grounds in Ponds That 

 Lack Them. Shelford (1911) has said that "the breeding 

 interests and the feeding interests of still-water food and 

 game fishes are distinctly antagonistic," As a pond grows 

 older the amount of rooted vegetation in it increases un- 

 til the whole pond bottom becomes thickly covered by it. 

 The decay of such vegetation adds to the water chemical 

 substances which serve as food for the microscopic plants 

 or algae (Pond, 1905). The algae form the basic food 

 for the microscopic animals. These in turn form the 

 food of younger fishes and from them a chain of nutri- 

 ent relations leads up to the adult fishes. Consequently 

 as a pond grows older and the number of rooted plants 

 in it is increased it contains more fish food. But this 

 same process which increases the food supply of fishes^ 

 tends to destroy the conditions necessary for their breed- 

 ing. The bottom becomes so thickly covered with muck 

 that there are no bare sand or gravel areas remaining 

 and these are necessary for some fishes. At the same 

 time the decay of the organic matter, which falls to the 

 bottom, may so use up the oxygen in the bottom waters 

 that fish eggs cannot live in them. 



If the above statement is correct then it follows that 

 old ponds, which contain few or no fish, may again be 

 made productive. They may be rich in the basic fish 

 foods, but lack the necessary breeding grounds. By re- 

 moving a part of the vegetation in water of suitable 

 depth so that sand or gravel bottom is exposed in some 

 places and a sparse growth of plants permitted in other 

 places, suitable breeding conditions may be restored. By 



