IV-105 



by invading needleruch, cordgrass, sawgrass, and other undesirable 

 plants. Hence, the marshes are burned annually, usually in the 

 fall, and are subsequently flooded to eradicate the pest plants 

 and enhance growth of threesquare (Figure IV. 2. 6). Dikes or other 

 water control devices are used to help minimize the intrusion of 

 salt water into the fresh or brackish water of the producing 

 marshes. Thus, the marshes managed for fur production are not 

 normally available for other valuable aquatic species, especially 

 shrimp and estuarine-dependent fish (Figure IV. 2. 7). 



Game Waterfowl 



The dependence of waterfowl on the estuarine zone is both complex 

 and not completely understood. The primary sport species, such 

 as mallards and canvasbacks, have been successfully adapted to 

 man-made changes in their environment, particularly those which 

 do not affect the nesting sites. In some cases, the construction 

 of roads, drainage canals, and other works have enhanced nesting 

 areas by stabilizing water levels, providing flood-proof nesting 

 sites and drought-proof rearing ponds. Furthermore, most species 

 do not appear particularly dependent on any aspect of the estua- 

 rine zone, being able to use freshwater marshes, lakes, and ponds 

 with equal ease. This ambivalence has been sharply enhanced in 

 the Gulf area by extensive rice cultivation and cattle farming 



