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Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-20
equally well in fresh and salt waters, in areas of primarily marine salinities,
manatees are well known for their desire to drink fresh water. They will
drink water from hoses, and frequently travel upstream into rivers and
canals, at least in part to reach freshwater areas.
Surveys and censuses of manatees have been performed annually for many
years by local, state and/or federal agency personnel. These surveys have
included aerial observations (typically fly-overs in fixed-wing aircraft
immediately after the passage of cold fronts) and tracking of manatee
movement by radio and/or satellite telemetry. The data, which were
compiled for the period from 1989-94 reveals a number of specific area where
there were repeated sightings (Figures 13a - c).
Based on the analyses of these data, the MPP identified ‘preferred manatee
habitats’ as areas with dense vegetation for feeding, freshwater sources for
drinking, and warm water refuges for warmth during the cold and further
identified “Essential Manatee Habitat” as “any land or water area
constituting elements necessary to the survival and recovery of the manatee
population from endangered status which may require special management
considerations and protective measures. The constituent elements include,
but are not limited to: space for individual and population growth, and for
normal behavior; available food sources with adequate water depth and
quality; warm and fresh water sources; sites for breeding and rearing of
offspring; and habitats protected from disturbances that are representative of
the geographical and seasonal distribution of the species.” It additionally
identifies eight such Essential Manatee Habitat areas (Figures 14 a - d). Each
of the six sub-regions that have been identified for the MFL project contains
at least one of these Essential Manatee Habitat areas.
In general terms, the manatee habitat areas that could be adversely affected
by reductions in the flows of freshwater include the following MPP
designations; 1) Fresh Water Sources; 2) Warm Water Refuges and; 3; Other
Aggregating Areas.
Fresh Water Sources
Regarding Fresh Water Sources, the MPP states that:
“Manatees utilize freshwater canal systems in Dade County,
particularly during warm weather. They travel through open flood
gates to access these areas. Manatees are observed as flood gates yearround, but aggregate at these locations in large numbers during cool
weather. Those flood gates where manatees are most frequently
Figure 13 a
Manatee Sightings – Northern Biscayne Bay
Source: Manatee Protection Plan. Miami-Dade Department of Environmental
Resources Management
Figure 13 b
Manatee Sightings – Central Biscayne Bay
Source: Manatee Protection Plan. Miami-Dade Department of Environmental
Resources Management
Figure 13 c
Manatee Sightings – Southern Biscayne Bay
Source: Manatee Protection Plan. Miami-Dade Department of Environmental
Resources Management
Figure 14 a – Essential Manatee Habitat Areas
Source: Manatee Protection Plan. Miami-Dade Department of Environmental Resources
Management
Figure 14 b – Essential Manatee Habitat Areas
Source: Manatee Protection Plan. Miami-Dade Department of Environmental Resources
Management
Figure 14 c – Essential Manatee Habitat Areas
Source: Manatee Protection Plan. Miami-Dade Department of Environmental Resources
Management
Figure 14 d – Essential Manatee Habitat Areas
Source: Manatee Protection Plan. Miami-Dade Department of Environmental Resources
Management
Valued Ecosystem Components
Freshwater Flow and Ecological Relationships in Biscayne Bay 4-28
observed are located on Snake Creek, Biscayne Canal, Little River,
Miami River, Tamiami Canal and Black Creek. Another popular
manatee fresh water source is a stormwater outfall structure on a canal
connected to Coral Gables Waterway. A daily pattern has been
observed by manatee trackers in Dade County during cold weather
months: many manatees leave Biscayne Bay in the morning and travel
up rivers and canals to the fresh water source where they drink and
rest, and will return to the Bay in the afternoon (Pers comm.., Kathryn
Curtin, USFWS, 1990).
The portion of Little River immediately downstream of the salinity
control structure is a consistent manatee gathering place during the
winter months. Manatees drink freshwater water which leaks through
the structure”.
Warm Water Refuges
Regarding warm water refuges, it is well known that manatees are attracted
to springs and the warm-water discharges from power plants during the
winter, however, due to its sub-tropical location, ambient water temperatures
in Biscayne Bay are thought to be warm enough for manatee use, “except
during prolonged periods of cold temperatures” (DERM 1995). There are no
springs in Miami-Dade County that are known to attract manatees. There are
two power plants in Miami-Dade County, and both are located in coastal
areas. The largest of these, the Florida Power and Light Company (FPL)
Turkey Point Plant uses a cooling canal system that has no direct surface
connection to Biscayne Bay, and therefore manatees are not attracted to this
facility. FPL also maintains a power plant in the Cutler area. The Cutler
Power Plant discharges thermally enhanced water into a tidal canal adjacent
to Biscayne Bay. However, this facility is intermittently used, and is not a
major aggregating site for manatees. FPL’s Port Everglades Power Plant in
Broward County does attract manatee in large numbers during the winter,
and some of these manatees travel back and forth from the warm water
discharge to foraging areas in Miami-Dade County.
Although there are no major sources of warm water in Miami-Dade County,
aerial censuses have documented that manatees that are in County waters
during prolonged periods of cold weather move upstream into rivers and
canals and into deeper, protected waters that tend to stay slightly warmer
than the shallow, exposed Bay (DERM 1995). Specific areas that are known to