The effort to protect this unique mammal must continue as its environment continues to change.
By ROBERT K. BONDE
Published January 9, 2004
Close your eyes and imagine yourself in a world where you had to eat, sleep and breathe on the highways.
Now imagine the numbers of cars on the highways increasing every day, and that those cars are going faster and faster. Every breath must be taken in the fast lane. You are an intelligent, long-lived creature, always on the guard 24 hours a day, seven days a week, for all the 60 to 70 years that you expect to live.
But one day you are not careful and you are struck by a car. If you are lucky, you live and are only scarred for life.
Strange as this scenario seems, a world similar to this exists today for the manatee in the waterways of Florida. These gentle creatures must live their entire lives in the congested canals and channels of the Southeast. Sharing these travel corridors with an increasing number of boats and ships each year intensifies the threat to the survival of this endangered species.
Manatees are curious, intelligent creatures that have found their niche in a unique order of mammals called the Sirenians. There are three species of manatees: the West Indian manatee, the West African manatee and the Amazonian manatee. The West Indian manatee has been divided further into two subspecies: the Florida manatee and the Antillean manatee.
Manatees are more closely related taxonomically to elephants, hyraxes and aardvarks than any other mammal. Distribution for all the Sirenians extends along the Earth's warmer, equatorial regions. Manatees cannot survive exposure to the cold for long periods.. In Florida, manatees have to locate warm water during cold periods, especially in the northern limit of their range. Each year as temperatures drop, some manatees travel hundreds of miles in search of warm water.
Loss of habitat from development in south Florida and destruction of natural water flow around the Everglades during the first half of the century, coupled with construction of power plants along the coasts, made it easy for the manatee facilitated the manatee's adaptation to extend its winter range north into areas with cold winter waters. Many manatees have learned to overwinter in the warm water discharges of these northern plants. Thus, today they are confronted with a dependence on artificial warm water sources. Unable to reclaim lost habitat in south Florida, manatees are stranded and could be literally left out in the cold if these plants were to shut down. Can manatees adapt over time while being subjected to these colder winter conditions? Only time will tell.
Able to reach a length of 12 to 13 feet and weigh more than one ton, these animals are quite agile in their aquatic environment. Their streamlined body reduces friction and their round, flattened tail supplies propulsion. They nurse their young from teats located under each front flipper. When viewed from above, there is no obvious external sexual dimorphism. Sex can only be determined when the animals roll over. Sparse body hairs are evident along their slate-gray skin, while algae and barnacles occasionally adorn their thick hide. They use their flippers and prehensile lips to manipulate items into their mouths, much like a third hand.
Biologists from the U.S. Geological Survey, as well as the Florida Fish and Wildlife Conservation Commission, several universities and oceanaria throughout the state, have been studying manatees for several years. Studies have evolved around natural history observations, aerial surveys, radio telemetry, salvage examinations of carcasses, feeding and habitat status studies, and captive husbandry research. This information is used by managers, biologists and lawmakers with the goal of removing the manatee from endangered species status.
With about 3,500 manatees in Florida, their recovery is far from over and will continue to be a slow process. I remain optimistic, however, because the manatee is a quick learner and adaptable, as evidenced by its ability to survive in many urbanized locations. But I am also worried that power plants cannot run forever, and if the increase in the number of registered boats in Florida is not limited we will continue to have high numbers of deaths.
Radio-telemetry studies of manatees have been ongoing for more than 25 years. It is the most successfully tracked marine mammal to date. We have learned that most tagged manatees have specific seasonal site fidelity. Some have home-ranges within a few miles in the course of the year; others will travel the entire coastline, making migrations in excess of 500 miles. These moves are often made in response to changes in water temperatures, as well as food preferences and fresh water availability.
One interesting manatee, Chessie, was radio tagged in Florida and traveled along the Atlantic seaboard to as far north as Rhode Island in summer. Chessie returned to the warmer waters of South Florida by winter and repeated that migration the following year as well.
One calf is born to each adult female every three years or so, although twins have been observed. Cow-calf bonding is very strong and generally lasts two years after birth. We believe that during these first two years of life with their mothers, young manatees are taught important and vital information for survival. Captive-born manatees, and very young rescued orphan calves, do not have this preweaning experience and may not have the knowledge necessary to find warm water or feeding sites in the wild.
Last year 358 dead manatees were recovered from Florida's waters. While several manatees are crushed each year in locks and flood dams, the major contributing human-related cause of death continues to be animals struck and killed by water vessels (93 individuals in 2002). Managers have addressed this problem by establishing new sanctuaries and by placing speed restrictions on boats. With little sacrifice on the part of boaters and fishermen, steps can be taken to allow for coexistence with our wildlife. It may take time before we see any long-term results from these actions.
Another potentially serious threat to manatees is the possibility of exposure to epizootic diseases or pollution while in large aggregations. Diseases could spread quickly among a group of 400 or 500 manatees nestled together to stay warm in a canal the size of a football field. Being semi-gregarious, manatees are mildly social and are often seen in groups. Hundreds of manatees have been observed feeding on large, massive seagrass beds. Applications of weed controlling herbicides must be monitored and levels of exposure to manatees kept to a minimum. Management of the resources and aquatic vegetation are a primary concern if manatees are to be around in the 21st century.
Every year several sick or injured manatees are rescued and taken to participating oceanaria for rehabilitation. Causes of rescue range from orphaned calves to boat strike victims to manatees entangled in crab trap ropes or fishing lines. A manatee can eat up to 100 pounds of vegetation a day, which puts a large financial and logistic burden on rescue facilities. Objectives outlined in the Florida Manatee Recovery Plan mandate that rehabilitated, healthy manatees be returned to the wild as soon as possible. Releases to date (more than 466 animals) have been very successful and are encouraging.
A catalog of photographs of manatees with distinct (or unique) scars and features have enabled us to monitor the movements and site fidelity of individuals throughout their range. More than 2,000 individual manatees are known and monitored with this system. Photographers go out into the field, primarily to winter aggregation sites, and take pictures of scarred individuals and note various behaviors. Work initiated more than 30 years ago is included in this data set, with photographs of known animals sighted this season from the Crystal River population dating back to as early as 1964.
I have been studying manatees for more than 25 years. They intrigue me, amaze me, and enthrall me. When I enter the water and see them, I look into the eyes of an animal that shows their anguish and a cry for help. Manatees are going to need our assistance and we as human beings can lend a hand, but at the same time we should feel pride in knowing that we are doing something to better the chances for survival of this unique marine mammal and by doing so helping to make this planet a better place for all to live.
- Robert K. Bonde works with the U.S. Geological Survey, Florida Integrated Science Center, Sirenia Project. His office is in Gainesville.
