By Matthew Schwartz

A recent Miami Herald article on manatee research in the Everglades does a good job of identifying some of the questions that still need to be answered with regard to this fascinating but still poorly understood species. However, the question of a major cause of manatee deaths within the boundaries of Everglades National Park is already well documented.

In a comprehensive study released in 2006, the U.S. Geological Survey examined the cause of death of 520 manatee carcasses recovered in the park between 1974 and 2004. Of the 286 carcasses where the cause of death could be identified, 115 or 40 percent were due to manatee boater collisions.

An additional 234 carcasses were cases where the cause of death could not be adequately determined. These were often found in remote areas of the park such as Whitewater Bay where advanced decomposition prevented identifying a cause of death. In a situation where collisions are so prevalent that manatees are often identified by the unique pattern of propeller scars on their bodies, it is assumed that a percentage of these were also killed by collision or by subsequent infection of an open wound caused by boat propellers. Carcasses that drifted out into open waters are often never recovered or identified.

Some suggest the possibility of putting in place slow-speed zones in areas where manatees are known to move and congregate. The difficulty will be in identifying all of these areas due to the manatee's propensity for exploration and constantly shifting movement patterns. These appear to be triggered by water temperature, salinity and other factors which the research currently being conducted will hopefully allow us to better understand. That being said, it is simply appalling for a leading cause of death of a federally listed endangered species to occur as a result of motorized recreation within a national park.

While recreational boating has a place in the park as a means of access, the National Park Service has other responsibilities that must be given far more weight as the service attempts to rewrite its general management plan for the park. In its own park-management guidelines, it is clearly stated that ``in cases of uncertainty as to the impacts of activities on park natural resources, the protection of natural resources will predominate.''

Research is called for to close some of that uncertainty but in this instance the data is already conclusive. Even more important are the mandates of the Organic Act of 1916 itself which established the National Park Service and its mission as follows: ``to promote and regulate the use of the . . . national parks . . . which purpose is to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.''

With this mandate of no impairment in mind, the Sierra Club has called for the establishment of no-motor zones in the shallowest areas of the marine waters of Everglades National Park. These will not only provide the manatee with some safe and undisturbed habitat, but will also protect the biologically indispensable seagrasses. Not only are they the primary source of food for the manatee, but they are the basis for practically all life in found in park waters.

Seagrass beds act as a breeding ground, nursery, food source and hunting ground for countless species. Thousands of acres of this resource have been destroyed by boat propellers and hulls traveling in waters that are simply too shallow to sustain them.

While the decision to close areas off to powerboats may be unpopular with some and thus difficult for park managers to make, we believe it is absolutely essential to the future protection of both the manatee and the entire marine ecosystem of Everglades National Park.

Matthew Schwartz is the political chairman of the Sierra Club of Broward County, Florida.