For the first time since 2011, state biologists have surveyed Florida's manatee population from the air. They counted 4,831, the third-highest number since counting began in 1991.

"We are encouraged by the relatively high count, especially given the high number of manatee deaths documented recently," said Gil McRae, director of the state's Fish and Wildlife Research Institute in St. Petersburg, which oversees the aerial surveys.

Last year, 829 manatees died in Florida's waterways, a record propelled in part by a toxic Red Tide algae bloom. The loss of about 15 percent of the state's estimated population of the iconic marine mammal seemed an ill omen for the species' future.

However, the biologist in charge of coordinating the 20 people from nine agencies who did all the counting cautions against making too much of the figures released by the Florida Fish and Wildlife Conservation Commission on Thursday.

"It's impossible to draw any inferences from this survey," said biologist Holly Edwards.

All that the high number proves is that the weather conditions were nearly perfect for finding manatees congregated around power plants and in springs.

The aerial surveys are designed to take advantage of winter weather, when cold-sensitive manatees gather at warm-water sites like power plant discharges. For the counts to be accurate, scientists say they need certain weather conditions, such as clear skies and temperatures below 50 degrees for three days.

When conditions are not perfect, not as many manatees show up in the survey. When winters turn too warm, scientists don't do a survey. After beginning aerial surveys in 1991 and 1992, scientists skipped surveys in 1993, 1994, 2008, 2012 and last year.

The surveys can produce wildly different numbers from year to year. In 2009, biologists announced that the count had produced a record of 3,807 manatees. In 2010, they broke that record, counting 5,067.

The differences are due not only to weather conditions but also the ability of the biologists in airplanes and helicopters to pick out how many manatees are bobbing in the water below.

"It's almost like flying over New York City on a busy day and seeing how many people are in the streets and using that to estimate how many people are in the city, without seeing how many are inside the buildings," longtime federal biologist Bob Bonde, co-author of Florida Manatee: Biology and Conservation, said in a 2007 interview.

This year's survey took place on Jan. 24 and 27, and found 2,317 manatees on Florida's east coast and 2,514 on the west coast. Biologists benefited from several consecutive, strong cold fronts preceding the count, Edwards said.

When manatees were first included on the federal endangered list in 1967, it wasn't because of the size of their population.

The then-chief of the National Aquarium, a St. Petersburg native named Craig Phillips, cautioned federal biologists drawing up the original list that manatees "may actually be more abundant than is believed at present, due to the fact that it is one of the most difficult of all totally aquatic mammals to observe in the wild."

Instead, federal officials classified it as endangered because of the loss of habitat and dangers from speeding boats — both still considered major threats.

Craig Pittman can be reached at craig@tampabay.com or follow him on Twitter at @craigtimes.