Survey Count Yields 3,116 Manatees
But Better Methods Exist For More Accurate
Population Assessment Say Scientists
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| Manatees gather at the warm water effluent of Florida Power and Light Company's Riviera Beach power plant, allowing researchers to get a head count during an aerial survey. (Photo by Cynthia Taylor, Wildlife Trust) |
Each year the Florida Fish & Wildlife Conservation Commission (FWCC) conducts at least one synoptic survey to count manatees. On February 13 – 15 of this year, the FWCC survey team counted 1,642 manatees on Florida’s east coast and 1,474 on the state’s Gulf Coast for a preliminary total of 3,116 manatees.
A synoptic survey is a statewide aerial survey designed to get a head count of individual manatees. The success of surveys is very dependent on weather conditions. If the weather is cold and clear, then manatees are gathered around warm water sites, making it easier to get a count. This year, the survey team had good conditions for counting with several days of cold temperatures that were also clear and sunny.
The synoptic surveys, which are required by Florida law, are often mistakenly used as a gauge of how the manatee population is faring, but most population scientists agree that the surveys alone cannot be used to evaluate the manatee population. “Synoptic surveys are not the most reliable way to determine overall manatee population,” says Patti Thompson, biologist and SMC Director of Science and Conservation. “They are simply a snapshot of the number of manatees seen on those days. We can’t infer anything about manatee population health and trends from the survey count.”
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Snug as a bug in a rug: a closeup shot of a manatee aggregation on a cold winter day. (Photo courtesy of
the U.S. Geological Survey, Florida Integrated
Science Center, Sirenia Project)
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According to FWCC biologists, a more accurate picture of the manatee population could be obtained by looking at factors such as past and projected population trends, area of geographic range and critical habitat, the number of mature individuals, and the probability of extinction. Thompson agrees. “There is ongoing research that utilizes annual adult survivability and other long term research that is better suited to assessing the health and stability of the population,” she says.
These research methods show that while the St. Johns and Crystal River manatee subpopulations are experiencing growth, the Southwest manatee population is probably declining and the Atlantic coast manatee population is perhaps stable but may be either slightly increasing or decreasing.
Ongoing threats such as watercraft collisions and red tide as well as threats to habitat like degradation of food sources and the loss of warm water areas that manatees need for winter survival also have to be considered.
“The St. Johns and Crystal River subpopulations that are doing well only account for about 16% of the total manatee population,” says Thompson. “The other 84% of the population is either stable or declining, so if we lose some power plants as winter warm water refuges or if red tide continues to take a major toll, then it could be bad news for the manatee population. We need to make sure these threats are under control before we take steps to downlist manatees, as the state of Florida is currently considering. We should not be tampering with the manatee’s status on the state or federal level until those threats are under control.”
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