These gentle marine giants face a number of threats to their survival, many of which are caused by humans.
The leading human-caused threat to Florida manatees is collisions with watercraft . Propellers and boat hulls inflict serious or mortal wounds, and most manatees have a pattern of scars on their backs or tails after surviving collisions with boats. Scientists believe that unless this cause of death is controlled, the manatee population will not recover.
The greatest long-term threat to manatees involves the loss of warm-water habitat  that manatees need to survive. At temperatures below 68 degrees Fahrenheit, the stress of the cold can become dangerous, or even fatal. Over the past 10 years, Florida’s manatees have had higher-than-usual numbers of deaths from cold stress. The winter of 2010 saw a total of 766 manatees killed, nearly 300 of them by an extended period of very cold weather.
Because residential development has greatly reduced the natural warm water springs used by manatees to stay warm, as much as two-thirds of the manatee population relies on the warm-water outfalls at electric power plants on cold winter days. A large number of manatees could be lost in the next few decades if natural areas are not available to manatees as aging plants are shut down or experience equipment failures. Their survival will depend on protecting natural springs and healthy habitat.
When humans disturb manatees, it can cause them to alter their breeding, feeding, sheltering and other natural behaviors, and puts them in harm’s way. Feeding manatees; using water to attract manatees to a boat, dock or marina; separating a mother and her calf; disturbing resting or mating manatees; chasing them from warm water sites; hitting or poking manatees; jumping on, standing on, holding onto or riding the animals - all of these actions can cause manatees serious harm.
A red tide is a naturally-occurring event that begins offshore in the Gulf of Mexico, when large amounts of certain species of algae bloom. This algae contains natural neurotoxins, which can be dangerous to humans and local wildlife. Once the bloom moves closer to shore, nutrient pollutants in agricultural or urban runoff can make the problem worse by fueling larger and more persistent blooms. Manatees come into contact with red tide in the shallow waters in southwest Florida. They can inhale red tide neurotoxins when they surface to breathe, and ingest them when they eat seagrass coated by the algae. The toxins cause seizures that, if severe enough, can prevent manatees from lifting their snouts above the water to breathe, which causes them to drown.
2013 was the deadliest year on record for manatees – more than 830 animals died. An unprecedented number of these marine mammals died from a large and persistent red tide outbreak in southwest Florida, while many more manatees have perished in Brevard County on Florida’s Atlantic coast following a massive dieoff of seagrass, their main food source.
Defenders closely monitors manatee mortality statistics with an eye on reducing the threats to manatees in the wild. You can keep track of them, too, by reviewing manatee mortality statistics on the Florida Fish and Wildlife Conservation Commission's website .