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Science Sector

By Tiare “TJ” Fridrich, Manatee Biologist

Boat strikes are the leading human-caused source of mortality for manatees in the state of Florida, with 17% of all manatee deaths attributed to vessel strikes in 2024. Manatees are especially predisposed to boat strikes because of their anatomy and life history. Manatees have evolved to travel long distances to find food and fresh water, an activity that requires a lot of energy. To use this energy most efficiently, manatees move slowly, undulating their paddle-like tail for propulsion. While they are able to swim at speeds up to 18 miles per hour in short bursts, manatees typically cruise along at three to five miles per hour.

Manatees move slowly because of their large size, with adults growing to between 800 and 1200 pounds on average. One of the reasons manatees grow so large is because they are aquatic herbivores, eating mainly aquatic plants. Plants, while plentiful, do not contain a lot of nutrients, so manatees make up for this by spending many hours a day eating. Manatees eat roughly 10% of their own body weight in plants each day and spend 6 to 8 hours a day feeding. Manatees have a large, complex digestive system that takes up a large portion of their internal body cavity, which acts to further absorb nutrients from their food. It takes up to a week for food to pass through their digestive system.

The aquatic plants that manatees eat grow along the banks of rivers, estuaries, and springs, or in the shallows where light can penetrate through the water. Because manatees spend so much of their day feeding in shallow water, this makes them especially susceptible to boat strikes. If a manatee is feeding in the shallows and is unable to move into deeper water, they may not be able to get out of the way of an approaching vessel. Additionally, a manatee cannot turn their head to look around for boats. They only have six cervical vertebrae, unlike most other mammals that have seven, and they must turn their entire body to look behind them. To investigate their environment, manatees rely on their 3,000 sensory hairs, called vibrissae, to detect water movement and nearby objects. The marine environment is noisy, too, and it can be difficult to determine what direction a sound is coming from. Sounds bounce off hard surfaces underwater, and the sound of a boat engine doesn’t always travel straight from the boat to a manatee’s ears.

When a manatee is hit by a boat, it is often the hull of the vessel that does the most harm, though propellers can do quite a lot of damage as well. A manatee’s lungs are long, flat, and positioned along their backbone, stretching along the top of their backs and surrounded by rib bones. Manatees always swim horizontally because of the position of their lungs, and when they come up to breathe, only their snout may be visible, with their body maintaining that horizontal position under the surface. When they are hit by the hull of a vessel, even at relatively slow speeds, their ribs can break and puncture their lungs, causing massive internal injuries. Often, a manatee hit by a boat will have trapped fluid or air in their lungs, making it difficult for them to submerge in the water since their lungs are a primary means of maintaining buoyancy.

The best way we can protect manatees from boat strikes is to boat slowly. Boating slowly protects manatees by giving the boat operator more time to react if they do see a manatee, as well as giving the manatee time to react, potentially reducing the severity of injuries in the event that they are hit. We can also avoid harming manatees by keeping our vessel in deeper channels and away from seagrass beds. Whenever we boat, it is also important that we have a spotter on the front of our vessel to look for any marine life, not just manatees, and that we wear polarized sunglasses to reduce glare. Protect our manatees from boat strikes by remembering that we share our waterways!