News

By Tiare “TJ” Fridrich, Manatee Biologist

Manatees are large, slow-moving aquatic mammals that regularly travel large distances along Florida’s waterways. Some manatees will swim hundreds of miles each year in search of food, fresh water, warm-winter habitat, social interaction, and safe places to rest. In Florida, manatees can be found in nearly every waterway navigable by boats, from freshwater rivers to coastal bays, which puts them at risk of injury or death from boat strikes. According to studies completed by the Florida Fish and Wildlife Conservation Commission (FWC), approximately 25% of all documented manatee deaths in Florida are a result of strikes from watercraft, and 1 in 4 manatees have been struck upwards of ten times in their lifetime.

To protect manatees from boat strikes, the Florida Legislature enacted the Florida Manatee Sanctuary Act in 1978. The Act declared all of Florida to be a refuge and sanctuary for the manatee and gave FWC the authority to establish boating zones to restrict the speed and operation of vessels to protect manatees from boat collisions. These zones, called manatee protection zones (MPZs), can also restrict entry to areas that are especially important to manatees, like power plant outflows and natural springs wherein hundreds of manatees gather in the wintertime to stay warm. By reducing speed limits in waterways with high manatee use, MPZs give boat operators more time to react when encountering a manatee, give manatees more reaction time to potentially avoid a collision, and, in the case that a collision cannot be avoided, reduce the severity of injuries a manatee sustains from the encounter.

While over 96% of all manatees in Florida have boat scars, manatees are more often killed by the blunt force trauma, or the impact, of being hit by the hull of a boat than by the propellers of the vessel itself. Blunt force trauma can cause broken or dislocated ribs and internal bleeding, and broken ribs can easily puncture lungs or other organs. It may be surprising to discover that an 18-foot boat is capable of fracturing manatee ribs at speeds of just 13 mph (11 knots), which is well below the speed needed for most boats of that size to get on plane (when the front of the boat lifts out of the water, reducing drag). The impact force of a boat strike on a manatee is a function of the speed of the boat (velocity is squared), so if the speed of a boat is doubled, the impact energy of a boat strike is quadrupled. We know that the most effective way to protect manatees from death and injury from boat strikes is by reducing boat speeds and adhering to manatee protection zones.