Deadly Waters (11 page)

S
olving mysteries is a large part of what wildlife biology is all about: Asking questions, looking for clues, recording observations. These are some of the essential steps in our attempts to peer into the lives of animals and understand how they live.

There has never been a shortage of mysteries in the Everglades. In the past, few white men traveled through the Everglades, partly because of superstitions about and fear of the marsh and its general inaccessibility. Until the middle of the 19th century, the region was described as a “series of vast miasmic swamps, poisonous lagoons, huge dismal marshes without outlet, a rotting, shallow, inland sea, or labyrinths of dark trees hung and looped about with snakes and dripping mosses, malignant with tropical fevers and malarias evil to the white man.”

Although the experiences of scientists and visitors alike have since eased our minds about such fears, the term “mysterious Everglades” still lingers. The mysteries of today range from the whimsical pursuit of the mythical “Skunk Ape”—the South Florida version of Bigfoot—to more serious questions, such as Why has the number of wading birds and other wildlife in the Everglades declined so dramatically? and How can these creatures be restored?

A mystery with similarities to the one you just read about manatees unfolded in early 1989. Biologists working in the Everglades found largemouth bass with mercury levels that were the highest in the state. Mercury, like the copper in this story, is a chemical element called a heavy metal that eventually concentrates in the bodies of the largest predators. Mercury is a nerve poison to people and other animals. Signs were posted at popular fishing spots throughout Everglades National Park warning people about the hazards of eating mercury-contaminated freshwater fish.

In the summer of 1989 one of the few remaining Florida panthers in Everglades National Park was found dead in the Shark River Slough area. A necropsy was performed. It revealed that the animal's liver contained an incredibly high level of mercury—more than a hundred times what is considered safe for people! In spite of this finding, veterinarians were not prepared to list mercury poisoning as the cause of death. They did say, however, that it may have been a contributing factor. Scientists became even more concerned when blood and hair samples taken from living panthers in this area showed higher than expected levels of mercury.

How did these panthers get such high levels of mercury in their systems? Maybe it was in the food they were eating. Scientists examined raccoons, one of the favorite foods of panthers living in Shark River Slough. Tests on raccoons in Shark River Slough showed they had higher levels of mercury than were found in raccoons living in other parts of the park. This was not surprising because these animals feed on mercury-contaminated fish and invertebrates. Since then, mercury has been found in many other predatory species, including spotted sea trout and birds, such as mergansers and cormorants.

Where does mercury come from? How did it get into the environment of Everglades National Park? Scientists have many theories. Mercury does occur naturally as a part of Earth's air, rock, and soil. However, some agricultural and land development practices may release more mercury into the environment. The burning of fossil fuels in power plants and waste incinerators also releases mercury into the atmosphere, often from quite distant parts of the globe. Mercury is found in batteries, dental materials, paints, and other products we use every day. Improper disposal of these products may release that mercury into the environment.

Although some progress was made in the 1990s to limit the incineration of medical waste––one of the main sources of mercury––the problem persists. In 2005, sampling of fish in Everglades National Park revealed high concentrations of mercury in mosquito fish––a favorite menu item for wildlife.

Since the late 1980s, scientists have learned more about how mercury moves through the Everglades environment, including how mercury interacts with other pollutants. And we are still learning what happens to contaminants such as mercury and copper once they enter the environment and what effects they have not only on fish, wildlife and their habitats, but also on human health. It is often years, if not decades, before we are able to prove that a specific chemical is having a harmful effect on our natural resources.

There are other mysteries in the Everglades that are much easier to solve. In fact, they really aren't mysteries at all. For example, I was recently shown a picture of a dead great blue heron. The shriveled and sun-bleached feathers and bones of the bird were hanging from loops of fishing line wrapped around a tree branch along the bank of the Harney River, deep in the Everglades backcountry. Every year countless numbers of water birds, like the pelican in the story, and other marine animals are found entangled in pieces of fishing line and other plastic trash that has been tossed into our nation's waterways by careless people.

Restoring and maintaining a healthy Everglades is an immense responsibility. Ultimately the solution lies with those who care about the future of the Everglades. Those who care about the future of our environment and its living resources—manatees or panthers, pelicans or great blue herons—will remember this: When we throw something away, such as obsolete computers, used mercury batteries, or old fishing line, there really is no such place as “away”—only someplace else! Those who really care will make an effort to reduce, reuse, and recycle.

Skip Snow,

Wildlife Biologist

Everglades National Park

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