Manatee Aerial Surveys
Aerial surveys are valuable for acquiring information on manatee distribution, relative abundance, and use of habitat types. The Florida Fish and Wildlife Conservation Commission (FWC) uses three types of surveys to assess manatee populations: distributional surveys, synoptic surveys, and power plant surveys.
AERIAL DISTRIBUTIONAL SURVEYS
Marine mammal biologists from FWC and other agencies use aerial distribution surveys to determine the seasonal distribution and relative abundance of manatees. Aerial surveys are sometimes flown to document the abundance of dolphins, right whales, and sea turtles.
Surveys are typically conducted in nearshore waters around the state. Flights are usually between four and six hours long and are most commonly flown every two weeks for two years. Most surveys are flown from small, four-seat, high-winged airplanes (Cessna 172 or 182) flying at a height of 150 m (500 ft) at a speed of 130 km/hr (80 mph). The flights are designed to maximize manatee counts by concentrating on shallow nearshore waters, where manatees and their primary food source, seagrasses, are located. Flight paths are parallel to the shoreline, and when manatees are sighted, the airplane circles until the researchers onboard are able to count the number of animals in each group. Scientists usually do not survey deeper waters. In urban areas or where waters are particularly opaque, some studies are made using small helicopters.
All aerial data are recorded on maps and entered into the Fish and Wildlife Research Institute's Marine Resources Geographic Information System (MRGIS) for spatial analysis. Survey data in the MRGIS are used as a primary source of data for management planning and decisions. The FWC Atlas of Marine Resources CD-ROM includes 31 data sets of manatee aerial distribution survey sightings, detailed aerial flight paths, and related coverages of bathymetry, shorelines, seagrasses, county boundaries, and aids to navigation.
Five other research groups are currently conducting manatee aerial distribution surveys in Florida:
- Jacksonville University surveys Duval County.
- Kennedy Space Center surveys upper Banana River.
- Dade County Department of Environmental Resource Management, Mote Marine Lab surveys Sarasota and Charlotte Counties.
- Chassahowitzka National Wildlife Refuge surveys the Crystal River and Big Bend areas.
The FWC's Imperiled Species Management and many other groups make frequent use of the data in the MRGIS system for making management decisions.
"Synoptic" means covering a large area. The synoptic surveys are winter aerial surveys that cover all of the manatees' known wintering habitats in Florida. FWC coordinates the interagency team conducting each synoptic survey.
These statewide interagency surveys are conducted after cold fronts pass through Florida, when the manatees gather at warm springs and thermal discharges from power plants and industrial plants. These surveys are useful in determining minimum estimates of manatee populations.
Manatees are counted during the coldest winter weather (December through March) because they congregate near known warm-water sites, such as natural springs, power plants, and deep canals, when temperatures drop. Counts are believed to be most accurate just after a cold front-when it is a bit warmer, clear, and windless-because manatees move to the surface to warm in the sun, making them more visible.
POWER PLANT SURVEYS
The waters around Tampa Bay area power plants were surveyed (1999-2003) for manatees each year from November through March. These surveys were flown near the Florida Power Corporation's Bartow plant and at the Tampa Electric Company's Big Bend and Port Sutton plants. Most of these counts were made to document manatee use of the thermal discharges in the waters near power plants. These surveys were also used as part of a manatee-boat interaction study to document manatee presence and boat use at certain areas.
Transect Aerial Surveys
In August 1997, as part of a long-term study to develop improved aerial survey techniques, FWC conducted transect aerial surveys in the Banana River, Brevard County. These counts will be used as part of a long-term assessment of population trends. A publication on the transect aerial surveys describes the benefits of transect methods for standardizing aerial survey counts and assessing population trends in wide, shallow bodies of water, like the Banana River (Miller et al. 1998).
Tampa Bay Power Plant Calibration Study
Researchers believe aerial surveys underestimate manatee populations, largely because some animals go undetected by observers. Design of most past aerial surveys focused on producing maximum counts rather than standardizing them. Since all manatees are not detected during surveys due to surface water conditions like turbidity and glare, some animals are not counted. Results of surveys that do not account for manatees not seen during the flight are not comparable over time or between locations. To improve surveys, scientists must develop means of accounting for manatees not detected during the survey, and counts must be adjusted to improve their accuracy.
In winter 1999-2003, FWC conducted aerial survey research at the TECO Big Bend Power Plant in Tampa Bay, Florida. The purpose of the study was to develop a mathematical model to formulate a correction factor to adjust winter counts of manatees at the TECO Big Bend power plants.
Between December and March 2003, researchers flew three sets of repeated aerial surveys over the TECO Big Bend Power Plant on the first, windless day following three different cold fronts. Aerial observers surveyed the plant to test the effectiveness of counting manatees during a 20-40 minute flight. One flight was flown in the morning (approximately 10:00 a.m.), and one was flown in the afternoon (approximately 2:00 p.m.) at an altitude of 500 ft-700 ft and speed of 70 kt.
Comparing the percentage of animals counted with the percentage of animals undetected by the observer provides data that are used to develop a correction factor, which can be applied to the initial count to adjust for animals missed during the survey. FWC staff members will apply knowledge gained from this study to obtaining better count estimates in locations throughout the state.