Mote Marine Laboratory

Sky High for Manatees

By: Nadine Slimak

Sure there are charts and maps and life vests — all the things you’d need to spend a day searching for manatees in the waters around Sarasota and Bradenton. But when the “captain” starts talking about air traffic control and water landings, you know this isn’t going to be just another day on the Gulf of Mexico.

From below, it must look like some recreational pilot has gone goofy — swooping circles in the air, buzzing down toward the water then back up to about 1,000 feet. Air traffic controllers call them the “manatee hunters,” and their task — stomach churning though it may be at times — isn’t goofy at all.

Call it flying for science.

Aerial manatee surveys fall into several categories. Some take place after intense or prolonged cold fronts when the mammals have sought refuge in warm water — anything less than 63 to 65 degrees Fahrenheit reduces their body temperatures and puts them at risk for potentially fatal cold stress. Dr. John Reynolds, Mote’s Manatee Research Program manager, has been counting manatees gathered in the warm power plant water discharges for more than 25 years. The repeated surveys have allowed him to perform sophisticated analyses of population trends.

Another type of aerial surveys, called “synoptic surveys,” are coordinated by state officials and give wildlife managers an idea of how many manatees can be counted on a single winter day — a sort of snapshot of the manatee population.

Members of Mote’s manatee program also do aerial surveys four times a month year-round. These surveys, which provide more information than just what manatees are doing on one winter day, have given scientists two decades worth of information about where manatees spend their time throughout the year.

New analyses of these long-term data is affirming some long-held beliefs about Florida’s manatees and might help answer some new questions so managers can make the best choices to protect this endangered species. “Sarasota County has been very proactive in supporting these surveys,” says Dr. John Reynolds, Manatee Program manager. “That’s helped us build this really remarkable database. We now have the power to assess long-term trends and do space and time analyses.” Now Manatee County is supporting surveys there as well.

On the morning of one recent trip, volunteer pilot Lew Lawrence of Sarasota warmed up the engine of a four-seat Cessna while Mote staff technician Carolyn Englund prepared her gear: a photocopied map of the coastline where her marks will indicate manatees, a GPS unit for general reference and to plot the survey route, headphones with a microphone so she can listen to weather reports and talk to Lawrence and polarized sunglasses to help her see manatees in the water.

“Among other things, we look for  mothers and calves and look at what area they’re in; is it sandy bottom or grass beds?” Englund says. “We also look at behavior. Are they resting, feeding or traveling?”

Spotting something the size of a Volkswagon Beetle from the air on a clear day in crystal clear water might sound easy. But it’s not as if manatees are painted a gleaming red, and their grayish or brownish color makes them pretty hard to spot in murky canals where they sometimes like to hang out. Englund, who’s had lots of practice, points out two near a dock in a canal. The manatees are doing a disappearing act — now you see them, now you don’t — as they surface to breathe then return to the bottom to rest.

Then, after spotting something suspiciously manatee-like somewhere else, Englund has Lawrence circle around so she can get another look. Circling is the order of the day — sometimes in a steep sideways bank or a downward spiral, just to make sure breakfast hasn’t settled. For five hours, Lawrence flies the coast from Sarasota to Tampa Bay as Englund looks out the open window for manatees. In all, the day nets 94 adults and 17 calves — a great count for the area.

Over the past couple of decades, counts of manatees in Sarasota County waters have fluctuated. The number of manatees counted increased through 2001, but has gone down a bit since then. Scientists think the lower counts might be due to changes in habitat, or the loss of some of the seagrass beds where manatees feed. In Manatee County — where Englund and Lawrence were flying — Mote is just starting regular surveys, and scientists hope to build a similar database to help identify population trends there.  

Scientists are especially interested in watching mothers and calves because ultimately the species’ survival depends on male to female ratios and the number of new young to replace the manatees that die. As Reynolds points out in his book, “Mysterious Manatees,” a group of 30-year-old humans has a different likelihood of sustaining itself over the long term than a group of retirees  — who aren’t having children and who are nearing the end of their lives — does. It’s the same idea for manatees.

After analyzing aerial survey data collected from 1994 through 2004, scientists have found that mothers with calves seem to prefer different habitats than groups of animals without calves. Their study, “Habitat Selection by Manatees in Sarasota Bay,” in review by the journal Marine Mammal Science, found that during cold winter months, all groups of manatees tended to congregate in warmer waters outside Sarasota Bay, regardless of whether calves were present. That indicates manatees sought warm water above all other habitats during those months.

During other times of the year — when the threat of cold stress wasn’t a factor — mothers with calves were more likely to be found in an area of Sarasota Bay closed to most boat traffic. The area has shallow water and extensive grass beds where manatees can feed.

“It’s been an unproven truism for years — that moms and calves use habitat differently, but this is the first instance in which it’s been demonstrated,” Reynolds said. “What this means is that all manatees are not created equally and that certain groups use habitat selectively, either seeking what they need or avoiding what hurts them. This gives managers a new opportunity to create protected habitats in ways that protect areas that key groups need.”

Learn more about: Manatee Research

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