GIS DECISION MODEL
Environment
Environmental variables affecting manatees.
Seagrass
Seagrass resources provide vital foraging resources for manatees. Seagrasses in close proximity to thermal refugia, where manatees are dependent upon food resources being nearby, are considered to be essential habitat.
More Information: FFWCC: Florida Port Facilities and their Impacts to Manatees
Water Depth
Manatees inhabit both salt and fresh water of sufficient depth (1.5 meters to usually less than 6 meters) throughout their range. They may be encountered in canals, rivers, estuarine habitats, saltwater bays, and on occasion have been observed as much as 3.7 miles off the Florida Gulf coast.
Water Temperature
Manatees are regarded as tropical marine mammals. Manatees prefer water temperatures to remain above 68°F (20°C). Prolonged exposure to lower water temperatures cause manatees to lose body heat and inadequately digest their food. This can lead to a condition classified as "cold stress" or death.
During the cold season, November to March, manatees seek out areas with warm water to meet their thermal requirements. Such warm water sources can be natural, such as springs (e.g. Crystal River), or artificial, such as power plant outfalls. Large numbers of manatees, often hundreds, can be found together at these sites during the cold season. Without warm water sources and sites in Florida, manatees would have a difficult time during extremely cold winters in our State.
More Information: FFWCC: Why are Warm Water Refuges Important to Manatees?
There is ample evidence that the proximity of forage to warm water sites is a factor primarily when water temperatures are coldest. Rose and McCutcheon (1980) noted this in their power plant research, "It appears that manatees will forego feeding in time of severe cold to remain in association with the warmer waters of these effluents, but will also move relatively great distances in search of food in response to warmer air temperatures." Shane (1984) also noted that manatees left the warm water effluent only during warm spells to feed and otherwise were relegated to the warm water refuge. Similar findings have been made at natural warm water refuge sites.
Levebvre and Powell (1990) noted that manatees may have preferred feeding grounds that are characterized by "less boat traffic, accessible grass beds much further away from the main channel (thus removed from speeding boats) and more quiet areas for resting and other activities."
Bibliography
Rose, P.M., S.P. McCutcheon 1980. Manatees (Trichechus manatus): Abundance and Distribution in and Around Several Florida Power Plant Effluents. Final Report, Prepared for The Florida Power & Light Company.
Shane, S.H. 1984. Manatee Use Of Power Plant Effluents In Brevard County, Florida. Florida Scientist. 47(3):180-187.
Lefebvre, L.W. and Powell, J.A. 1990. Manatee Grazing Impacts on Seagrasses in Hobe Sound and Jupiter Sound in Southeast Florida during the Winter of 1988-1989. Final Report prepared for the Marine Mammal Commission in Fulfillment of Contract T62239152.