U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3002

 February 2009

Integrated Science: Florida Manatees 

and Everglades Hydrology

Printed on recycled paper

Introduction

Restoration of the Everglades requires the implementation of dozens of separate construction components 

staggered over time and across the landscape; thus, effects 

on habitat and species will be realized on different time and 

spatial scales. Predicting and monitoring restoration effects 

on Florida manatees, which are known to make extended 

movements, will be incomplete if modeling and monitoring 

are limited to the smaller areas defined by the various 

restoration components. U.S. Geological Survey (USGS) 

efforts, thus far, have focused on (1) collecting manatee movement data throughout the Ten Thousand Islands (TTI) region, 

and (2) developing an individual-based model for manatees 

to illustrate manatee responses to changes in hydrology 

related to the Picayune Strand Restoration Project (PSRP) 

(fig. 1). In 2006, new regional research was begun to extend 

an Everglades hydrology model into the TTI region; extend 

the manatee movement model into the southern estuaries of 

Everglades National Park (ENP); and integrate hydrology and 

manatee data, models, and monitoring across the TTI region 

and ENP. Currently (2008), three research tasks are underway 

to develop the necessary modeling components to assess 

restoration efforts across the Greater Everglades Ecosystem.

Linking the Manatee Individual-Based Model 

with a New Ten Thousand Islands Hydrology 

Model and an Everglades Model

To evaluate how proposed restoration changes will 

affect the endangered manatee, it is necessary to (1) apply 

the Flow and Transport in a Linked Overland/Aquifer 

Density Dependent System (FTLOADDS) hydrology 

model to the Everglades area covered by the Tides and 

Inflows in the Mangroves of the Everglades (TIME) 

hydrology model, (2) extend the TIME model into the TTI 

area, and (3) integrate the hydrology model output with an 

individual-based manatee model. The FTLOADDS model 

simulates key hydrologic parameters that manatees respond 

to, including salinity, water level, and water temperature. 

To improve its value for evaluating manatees across the 

Greater Everglades, the model is being developed and applied 

in the TTI region south of U.S. Highway 41, including the 

PSRP area and the Big Cypress region. This objective 

is critical because both areas are important to manatees 

and are identified as priorities in the U.S. Department of 

the Interior Science Plan. Telemetry data collected from 

radio-tracked manatees in the region will be analyzed to 

help calibrate the FTLOADDS model and parameterize the 

response of manatees to restoration (fig. 2). 

Figure 1. Study area, showing general locations 

of the Ten Thousand Islands and Everglades 

National Park, south Florida. 

Manatees (Sirenia Project photo)

0 10 20 30 40 KILOMETERS

0 10 20 30 40 MILES

Everglades

National Park

Miami

Naples

Picayune Strand State Forest

Ten Thousand Islands

National Wildlife Refuge

Big Cypress

National Preserve

SOUTH FLORIDA

Florida Integrated Science Center
The coupling of the FTLOADDS model and the manatee 

model will allow researchers to study the relations 

between hydrologic conditions and variables, such 

as manatee movement and habitat use. Coupling the 

FTLOADDS and Across Trophic Level System Simulation (ATLSS)-style models will provide a useful tool for 

comparing the response of manatees to different hydrologic restoration scenarios.

Modeling Hydrology and Thermal Properties of 

Canals and Basins Used by Manatees as Winter 

Refuges

Cold stress is a major source of winter mortality for 

Florida manatees. Previous USGS research has shown that 

during cold periods, satellite-tagged manatees increase 

their use of the inshore canal systems that serve as passive 

thermal refuges (figs. 3, 4). During much of the winter 

season, vertical profiles at these sites indicate a halocline 

of warmer saltwater trapped below a cooler freshwater 

EXPLANATION

MANATEE

LOCATIONS

MANATEE

LOCATIONS

10 15 20 25 30 35

TEMPERATURE, IN DEGREES CELSIUS

A

B

FRESHWATER

SUBMERGED AQUATIC VEGETATION

TRAVEL CORRIDOR

0 1 2 3 5 KILOMETERS

0 1 2 3 5 MILES

4

4

EXPLANATION

Figure 2. A network of 

destination nodes is 

used to parameterize 

the manatee model. 

Nodes are determined 

by tracking manatees 

via Global Positioning 

System transmitters, 

and are typically 

associated with critical 

resources (submerged 

aquatic vegetation 

and freshwater) and 

connecting travel 

corridors.

Figure 3. Modeled temperature output during warm and cold 

winter periods. The black dots represent field data from one 

manatee tracked with a Global Positioning System transmitter 

during periods when the model predicted (A) overall warm 

water in the region, and (B) an inshore warm area during a 

period of overall cold water. 
A related integrated research and monitoring effort is 

being initiated in partnership with the South Florida Water 

Management District. The PSRP will attempt to restore 

sheetflow hydrologic conditions across a broad area by 

reducing and diverting flow from the four large canals 

located north of U.S. Highway 41 that drain into the Faka 

Union canal. USGS researchers will assess the probable 

effect of planned hydrologic changes on warm-water 

refuges, freshwater resources, and other critical habitat 

on manatee movements and exposure to environmental 

stresses. Monitored patterns of hydrologic change and 

associated manatee responses will be used to further 

validate and improve the hydrologic and manatee models. 

Developing and Implementing a Regional Aerial 

Survey Monitoring Design that Integrates Ten 

Thousand Islands with Everglades National Park

Aerial surveys, although often challenging, offer the 

best opportunity to monitor the population across the entire 

region in a cost-effective and scientifically robust manner 

(figs. 6, 7). 

Figure 4. Aerial photograph of the Faka Union (Port of the 

Islands) basin. This is the main passive thermal refuge in the 

Ten Thousand Islands area, at times harboring more than 

300 manatees during cold winter weather. Photograph by the 

Florida Department of Environmental Protection. 

lens (fig. 5). The resulting thermal inversion is used by 

manatees to stay warm and avoid potentially fatal hypothermia. The hydrologic process producing the halocline, 

and how restoration may disrupt its thermal properties, 

is not well understood. The objective of this task is to 

measure and model the three-dimensional properties of 

several of these sites in the TTI. This monitoring and 

modeling effort will provide important information for 

characterizing the salinity and temperature regimes of 

canals used by manatees and other cold-intolerant fauna/

biota, such as invasive, exotic fish species. 

Figure 6. Aerial surveys for manatees are a challenge in the Ten Thousand Islands and Everglades National Park. Photograph by the Fish and 

Wildlife Research Institute, Florida Fish and Wildlife Conservation Commission. 

Warm saline water

2-3 Meters

3-4 Meters

Cool fresh water

Spillway

FAKA UNION CANAL PORT OF THE ISLANDS BASIN

Figure 5. Vertical profile of the Port of the Islands basin, 

showing the halocline that allows for the pooling of warm 

water in the deeper parts of the basin.
The main objectives of this study are to: 

•	 Develop valid statistical approaches to document 

changes in manatee distributions and abundance 

in association with habitat variables incorporated 

in the models; 

•	 Develop and implement a regional manatee monitoring design for pre- and post-restoration assessments, 

integrating TTI with ENP; and 

•	 Provide an independent dataset for validation of 

the predictive manatee/hydrology models. 

Several statistical approaches to estimate habitatpatch occupancy rates and abundance from aerial survey 

data at TTI are being evaluated, including the proportion of area occupied, based on presence/absence data, 

hierarchical models, and removal models.

For more information~~

Comprehensive Everglades Restoration Plan: Home page: 

http://www.evergladesplan.org/

U.S. Geological Survey Sirenia Project Manatee Research: Home 

page: http://fl.biology.usgs.gov/Manatees/manatees.html

Figure 7. Flight paths 

for fixed-transect 

(blue) and distributional 

surveys (pink) being 

evaluated for monitoring 

manatee abundance 

and distribution in the 

Ten Thousand Islands 

National Wildlife Refuge.

0 5 10 KILOMETERS

0 5 10 MILES

Ten Thousand Islands

National Wildlife Refuge

Everglades

National Park

Picayune Strand State Forest

FIXED TRANSECT SURVEYS

DISTRIBUTIONAL SURVEYS

EXPLANATION

Authors~~

Catherine A. Langtimm1, Eric D. Swain2, Bradley M. Stith3, 

James P. Reid1, Daniel H. Slone1, Jeremy Decker 2, 

Susan M. Butler1, Terry Doyle4, and R.W. “Skip” Snow5

1 U.S. Geological Survey, Florida Integrated Science Center, 

 Gainesville, Fla.

2 U.S. Geological Survey, Florida Integrated Science Center, 

 Ft. Lauderdale, Fla.

3 Jacobs Technology, Tampa, Fla. (Contracted to USGS)

4 U.S. Fish and Wildlife Service, Ten Thousand Islands National 

 Wildlife Refuge, Naples, Fla.

5 National Park Service, Everglades National Park, 

 Homestead, Fla. 

Suggested citation~~

Langtimm, C.A., Swain, E.D., Stith, B.M., and others, 2009, 

Integrated Science: Florida Manatees and Everglades Hydrology: 

U.S. Geological Survey Fact Sheet 2009-3002, 4 p.