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Biology 103
2002 First Paper
On Serendip

Manatees and the Human Fault Factor

Katie Campbell

Manatees appeared on earth during the Eocene period about 50 to 60 million years ago. In general, adult manatees are about twelve feet long and weigh 1000 to 1500 pounds (1). They require warm water, a supply of "submerged, emergent, and floating plants" (3) such as hydrilla, turtle grass, ribbon grass, and manatee grass (4) for food, shelter and breeding grounds. Manatees are very gentle sea mammals whose curious personality leads humans to perceive them almost like their companion pets. Although manatees are playful, "scratch[ing] themselves on poles, boat bottoms, and ropes," they "do not seek interaction" (4) with people. Their humble mannerisms and general slow reactions do not mesh well with the increasing fast pace human life on Florida waterways. "More than 90% of direct manatee mortality" caused by humans is a result of boat accidents (5). Most often manatees are hit in their state of "torpor" or rest when they float near the surface of the water and are in the direct line of contact with boat propellers. Within the past few years the number of manatees killed by watercraft has remained steady, in the high seventies and low eighties. In 1999, a record high of 82 manatees were killed in such situations.

In some "controversial protection measures" (5) boats have posted speed limits on the water and boaters are advised for certain behavior, like to wear polarized sunglasses so that manatees close to the surface of the water can be seen more easily. One might assume then that the resulting boat collision deaths would decrease. This year, 2002, however, has already proved this idea wrong. Reports from the Florida Marine Research Institute state that this year up as recorded to September 27, 83 manatees have already been killed by human contact (6).

Not only do collisions with watercraft cause many manatee deaths a year but the phenomena of algae blooms, otherwise called red tide, account for many other manatee deaths. Harmful algal blooms (HABs) are caused by the cycle of algae in the sea. The germination of algal cysts can only happen in warm temperatures with increased light (7) . This obviously follows the pattern of manatees' habitats. When the cysts break open and result with a simple reproduction of a cell, it then "blooms," cells divide exponentially. Their concentration can cause toxicity in the water, accumulating in "dense, visible patches near the surface of the water" (7). The species which commonly poison manatees, found in the Gulf of Mexico is Gymnodinium breve.

Even though we want to attribute the loss of manatees by algal blooms to natural phenomena, it is obvious that certain human actions contribute to the worsening HAB situations. In the past few decades, the resultant deaths have increased while HABs have existed for years and so it poses the question as to why manatees are now being so affected by this. Human interaction with the environment has inevitably caused change in the environment which has then affected the manatees' response to HABs. Due to pollution, algal blooms have become more concentrated. Pollution also causes decreased resistance in manatees. Construction has destroyed wetlands which used to filter pollution. Habitats suitable for the manatee population become less and less with the same construction and so more manatees then congregate in the same area (8). The most popular area has become Crystal River which flows about seven miles into the Gulf of Mexico from Florida. The manatee's "need for fresh or low salinity drinking water" pulls them towards Crystal River and its containment of many major springs also provide for warm water, even when the waters of the gulf turn cold for the winter (1). Therefore, when two hundred or more manatees migrate up Crystal River every winter, their presence in close quarters makes the spread of infectious disease and toxins, like red tide, spread more quickly than otherwise.

These issues of manatee endangerment in Florida spark debate with the question of why manatees are considered endangered and then how should they be protected. Currently the approximately 2500 manatees of Florida are protected under the Endangered Species Act of 1973 and the Federal Marine Mammal Protection Act of 1972 (3). Many counties in the state of Florida attempt to further protect manatees by developing their own regulations. The population of Florida, however, argues over the development of better protection for manatees. Currently this can be seen with the petition submitted by the Coastal Conservation Association of Florida to re-evaluate manatee's definition as an endangered species under the Florida Endangered Species Act (2). This argument of certain groups in Florida over the protection of manatees and their definition as an endangered animal is a defensive reaction to human's direct involvement in destroying the species.

Clearly manatees have existed for millions of years and have undoubtedly changed over time. Their gestation period of thirteen months means that they only reproduce every two to five years and their change occurs slowly (3). It is then doubtful that manatees would be able to grasp the new development in red tide concentration, etc to develop different, more efficient immune systems to survive this destruction. Numbers like "20 % of the total population d[ying] in 1996 alone," it is in "serious doubt as to the manatees' survival into the next century" (4). Obviously, humans have not killed off every manatee with direct collision accidents. In fact the eight categories of death for manatees include three human related occurrences like boat collisions or death by a flood gate and five categories of "natural" causes like diseases and toxins (9) . While manatees may not be killed a majority of the time by human contact, 44 % are killed. And even though the majority of deaths are declared "natural," humans' involvement and interaction with the environment has changed and effected the environment in which the manatees live. Therefore, no matter what the particular stated cause of death is of manatees, somehow their deaths and so their endangerment as well, can be linked to humans.


World Wide Web Sources

1)Manatee Introduction and Background, part of The Florida Water Story homepage.

2)The Future of the Florida Manatee: And Ongoing Concern, recent opinion piece written on the petition to reconsider manatees' placement under the Florida Endangered Species Act.

3)About manatees..., a general description and explanation of manatees and their behavior.

4)Manatees, People---&The Buddy System, part of The Florida Water Story homepage.

5)Manatee Protection Efforts, part of The Florida Water Story homepage.

6)Number of Manatees Killy by Boats Reaches Record High, recent article (September 27, 2002) on number of manatee deaths this year.

7)What are Harmful Algal Blooms (HABs)?, general overview of how algal blooms work.

8)Manatee Habitat & Water Quality Issues, part of The Florida Water Story homepage.

9)Descriptions of Manatee Death Categories, general overview of categories used to determine death statistics.

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