Florida manatees rely on warm-water refuges during the winter months when water temperatures go below 68°F. This includes natural springs, thermal basins and power plants. The precise temperature threshold at which manatees would die from the cold is unknown, however cold tolerance seems to vary between individuals.
There are 14 major warm water discharges (10 power plants, 4 natural springs) at which 50 or more manatees aggregate near during the winter. Thermal basins act as another refuge, however it is unlikely that it could sustain a group of manatees for prolonged periods due to gradual cooling and lack of an independent heat source. The power plants used by manatees today were built between the 1940’s to the 1970’s and most of them are just about ready to be shut down. This presents a problem since the manatees have become dependent on these heat sources. Temporary shutdowns in the past have proven this, and the manatees continued to aggregate near these areas even though they were shut down.
Due to their body shape, size and low-nutrient diet, manatees have a difficult time staying warm. During years of extreme winters, manatee deaths spiked due to cold-related stress. Management strategies have been put in place to monitor the population as well as look for alternative warm-water refuges.
Today, Florida manatees have been petitioned to be downlisted from endangered to threatened for the first time since they were first listed in 1967. Although this is good news, it may be a little too premature since it is uncertain when exactly the power plants will retire. It’s taken manatees over 50 years to become this reliant on power plants so it is reasonable to assume that it could take the same amount of time to wean them.
Other threats to Florida manatees include habitat loss due to coastal development as well as collisions from boats. These things along with the uncertainty of power plant retirement leaves an uncertain future for Florida manatees.
You can read the study here for more info.