The first method increases mortality by predation during the early 

 life stages; the second prevents hatching. 



Open-Marsh Water Management 



Open-marsh water management for mosquito control is based on a 

 simple natural fact that fish devour large quantities of larvae. Of all 

 possible mosquito control methods, the open-marsh system interferes least 

 with normal wetland function and is recommended as the primary means of 

 salt-marsh mosquito control [146]. The cost appears to be justified by 

 effective, long-term control of mosquito breeding. It requires con- 

 siderable planning, surveying, and engineering, as well as biological 

 study by entomologists and wildlife biologists [147]. The approach is 

 now feasible throughout most coastal salt marshes although it has yet to 

 be adapted to the mangrove tidelands of Florida. 



The open-marsh method is designed to deprive mosquitoes of suitable 

 breeding habitat and increase their vulnerability to predation. When 

 storm or spring tidewaters are retained in isolated pockets (ponds, salt 

 pannes, and other depressions) in the marsh for periods of 4 to 10 days 

 or more, a high potential for mosquito breeding is created. Effective 

 control is obtained by connecting the isolated pockets to the natural 

 drainage system of the marsh with properly designed channels. These 

 provide access to all potential breeding areas for mosquito-eating minnows 

 such as killifish and mosquito fish. The system must also include suffi- 

 cient deeper, permanent water areas, where fishes can reside during low 

 water periods (Figure 46). 



Open-marsh water management has already demonstrated effective 

 control of mosquito breeding without harm to marsh vegetation, while 

 increasing the populations of many important marsh organisms [148] [149]. 

 The connector channels, or radials, also facilitate the transport of sus- 

 pended organisms and nutrients between marsh and estuary and improve the 

 function of the coastal ecosystem. If constructed correctly, channels 

 are of great value in mosquito water level management because they elimi- 

 nate the routine need for insecticides, as has been demonstrated in 

 Cumberland County, New Jersey [147]. 



In open-marsh water management, the channels should be dug only to 

 the depth and width necessary to connect the isolated depressions to the 

 pond-channel system. A rotary ditcher or the equivalent is effective 

 for digging the channels in grassy marsh areas. In reviewing plans for 

 channel excavation, it is important that such machines disperse the 

 channel spoil evenly over the marsh rather than dumping it in piles, 

 which may impede tidal flow [147]. 



176 



