Human Related Mortality | Natural Mortality

Research over the last several years has attempted to identify and quantify West Indian manatee distribution, population size, and causes of manatee deaths, most of which are directly related to human contact or encroachment. If these sources of mortality are not controlled, the manatees may become extinct.

Human Related Mortality Loss of Habitat Ultimately, loss of habitat is the most serious threat facing the manatee (as well as other Florida wildlife) today. Florida, the fourth most populous state in the nation (based on 1994 figures) is experiencing unprecedented growth. Nearly 1000 people are moving to this state every day and, in 1995, over 41 million people visited Florida. A status report published by Defenders of Wildlife in 1995, "Endangered Ecosystems: America's Vanishing Habitat and Wildlife," showed that Florida's ecosystems are more at risk than any other state in the U.S. because of development pressure. The growth in human population with its added pollution, litter, and boat traffic, has degraded and / or eliminated manatee habitat. Many fresh water and marine grassbeds have been lost due to water pollution, herbicides, surface runoff, propeller dredging, and dredge and fill projects. There are very few places left where manatees are free from danger, stress, and harassment posed by human activity.

Watercraft Collision West Indian manatees can swim up to 20 miles per hour, but they usually swim about three to five miles per hour. Because the manatee is slow-moving, needs to surface to breathe air, and prefers shallow water, it is vulnerable to boat hits. Sensing danger, the manatee will attempt to get away, but often there is not time to get out of the path of a speeding boat. And frequently there isn't sufficient depth to dive deeper. Consequently, the manatee suffers injury and death due to the crushing impact of the hull and / or the slashing of the propellers. In the case of large power vessels and barges moving through shallow waters, the manatee may be caught between the vessel and the water bottom, or the vessel and docking structure, and crushed.

Pollution Water pollution caused by many of the items we use in our daily lives (pesticides, herbicides, detergents, etc.), as well as storm water runoff and industrial chemicals, may poisen waterways, food sources, and manatees themselves. Oil exploration and possible oil spills are potential threats to all marine and estuarine habitats.

Litter Debris in waterways, such as discarded fishing line and hooks, plastic 6-pack holders, plastic bags, etc., are dangerous to manatees and other forms of wildlife. Entanglement in or ingestion of monofilament line / litter, carelessly left floating with aquatic plants have caused manatee injuries and even death. Crab trap lines and hoop nets used by commercial fishermen can also cause entanglement problems for manatees.

Harassment / Vandalism Harassment by boaters, divers, swimmers, and people fishing can force manatees to leave preferred habitat such as warm water refuges. Harassment can also lead to separation of mother and calf. Harassment refers to any act which causes the manatee to change its behavior and can include: pursuing, chasing, poking, prodding, grabbing, riding, and feeding manatees or giving them water from a hose. (This disrupts their normal behavior and conditions them to take food or water from people. Some people may use this opportunity to feed them dangerous non-food items or harm the manatee in some way.) Accounts of vandalism and even poaching have been reported in Florida and resulted in several manatee deaths. Save the Manatee® Club supports passive observation (observing from a distance) as the only way to interact with manatees and all wildlife.

Flood Control Structures Manatees can be crushed in the closing of flood gates and canal locks that are used to control water levels throughout the state. This problem is particularly acute in south Florida where there are many water control structures. Deaths due to drowning have also occurred when the tremendous suction created by water rushing through opening gates pins animals under the water. In recent years, the South Florida Water Management District and the U.S. Army Corps of Engineers have been working to monitor, and improve technology controlling the opening and closing of these structures to help prevent this type of death from occuring.

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Natural Mortality Cold Weather During winters in Florida that have been unusually cold, an increase in manatee mortality has been documented. Manatees cannot tolerate temperatures below 68 degrees F. (20 degrees C.) for long periods of time. Researchers believe that individuals affected by the cold cannot produce enough metabolic heat to make up for heat loss due to environment.

Red Tide In 1982 an outbreak of red tide - a toxic water-born, microscopic marine organism - occurred in southwest Florida and was believed to have contributed to the death of 37 manatees. Many of the dead manatees had accidentally ingested tunicates or sea squirts which contained concentrations of these toxic organisms. The sea squirts were probably ingested as the manatees fed in surrounding seagrass beds.

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