121 



Foxes, weasels, opossum, and bobcats are not sought for their fur 

 but may occasionally be trapped (fig. IV.2.5). 



For economic levels of fur production, the marshes must be man- 

 aged specifically for the fur bearers. This means control of undesirable 

 plants, prevention of excessive populations and, in some cases, control 

 of predators. The primary food plants are threesquare and cattails; 

 these, however, are easily supplanted by invading needleruch, cord- 

 grass, 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 (fig. 

 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 pro- 

 ducing marshes. Thus, the marshes managed for fur production are 

 not normally available for other valuable aquatic species, especially 

 shrimp and estuarine-dependent fish (fig. IV.2.Y) . 



Game umterfoiol 



The dependence of waterfowl on the estuarine zone is both complex 

 and not completely understood. The primary sport species, such as mal- 

 lards 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 estuarine zone, being able to use fresh- 

 water marshes, lakes, and ponds with equal ease. This ambivalence 

 has been sharply enhanced in the gulf area by extensive rice cultivation 

 and cattle farming which enable many species, such as the white- 

 fronted geese, to shift habitats away from estuarine marshes. Other 

 species, such as Canada geese and mallards, have demonstrated even 

 more adaptability, many remaining the entire winter in the freshwater 

 bodies of the Midwest (fig. IV.2.8). Many sea ducks feed upon small 

 crustaceans, fish, and insects that are estuarine-dependent. These ducks 

 have not learned to feed on agricultural lands, and tend to migrate to 

 deeper saltwater environments during the winter. 



In summary, while game waterfowl are frequently observed in the 

 estuarine areas, they do not appear dependent upon specific estuarine 

 conditions. There are some exceptions, such as the American brant, 

 but research has not determined the relationship between altered hab- 

 itat and declining numbers. 



OmamentaX hirds 



Shore and sea birds are a particularly aesthetic attraction among 

 the national fauna. However, they rarely have a direct tangible eco- 

 nomic value, except as a component of the natural ecosystem. These 

 birds are generally more dependent upon estuarine conditions than the 

 more mobile waterfowl, and have demonstrated a greater sensitivity to 

 the overall encroachment of man. The saga of the virtually extinct 

 Avhooping crane is well known and documented; and the trials of 

 several other groups, such as the egrets, have received periodic public- 

 ity. Among the bird life most threatened by changing environmental 

 conditions, especially in the estuaries, are the. larger fish-ea.ters of the 

 Nation's coast. 



