Biological threats

Issue 4 > Meet the Managers > Water quality issues: Biological threats
Didymo, or

Didymo, or "rock snot," chokes streams.

EPA photo.

Non-native, invasive plants and animals

  • Didymo, or “rock snot,” is native to some parts of the United States, but can threaten streams where animals aren't adapted to it. Didymo spreads easily on fishing and water equipment such as nets, poles, boots, and buckets. It is not in the park yet, and we hope to keep it that way! Rock snot feels like cotton; it’s not slimy like other algae. It coats rocks in a mat that can be 8 inches thick and destroys stream habitat for caddisfly, mayfly, and stonefly larvae (and many other animals), limits light and streamflow, and chokes out native aquatic plants.

    Didymo is now found in all east Tennessee tailwaters, which trout anglers who fish Smokies streams commonly visit. Therefore the park is asking all anglers to clean their wading boots in a 10% bleach solution and thoroughly dry their boots prior to visiting any park waters. You can read more about didymo from the EPA, and check the current distribution of didymo in the U.S. Click the back arrow to return to this page.
  • New Zealand Mud Snails are another non-native invasive species threatening the waters of the United States. Mud snails are prolific spawners that cover stream bottoms and all hard surfaces, causing massive declines in native insects and fish populations. Although currently are found mostly in the western United States, they are spreading east and anglers must try and prevent their spread. Click for more information about the mudsnail and view a map of its current distribution in the U.S. Click the back arrow to return to this page.
  • Whirling Disease, caused by a parasite, sickens salmonids (such as trout). It has been in the eastern United States for several years, but is most severe in the western U.S., where it has caused major declines in trout populations. Whirling disease is just one more example of a non-native aquatic species that threatens streams and their biota. It is our shared responsibility to protect our National Parks and other preserved lands from these invaders by cleaning our gear and taking precautions to prevent their spread. Click for more information about whirling disease. Check out an interactive map of whirling disease in the U.S. to see how whirling disease has spread and why biologists are concerned with its presence.
USGS researchers capture and swab frogs for chytrid fungus.

USGS researchers capture and swab frogs to test for chytrid fungus.

NPS photo.

Aquatic diseases

We most often see two diseases that infect amphibians in the Park:

  • Ranavirus infects tadpoles and salamanders, and is fatal
  • Bd and chytrid fungus are two forms of the same disease that devastates amphibian populations. Animals can carry Bd and not be sick with chytrid fungus (just as humans can be infected with HIV but not be sick with AIDS). Some in the park have deformed limbs and mouthparts, the most common signs of the disease, although infected animals may not show signs

Both of these diseases are responsible for massive amphibian declines worldwide. Diseases such as ranavirus and chytrid have resulted in a worldwide extinction rate that is 211 times higher than in the past. Many species in other parts of the world have already disappeared, and others are in danger of doing so, although populations at the Great Smoky Mountains remain stable.

U.S. Geological Survey scientists came to the park in spring, 2009 and tested amphibians in Cades Cove ponds for Bd, after university researchers noticed amphibians with symptoms of chytrid fungus. Other researchers are gathering data about time and location of outbreaks to understand trends of disease increase and decrease.


Non-native bait

A wriggling treat on a hook seems like a good way to catch a fish; but it's not that simple. The park bans bait for fishing for these reasons:

To prevent introduction of non-native species. Where in the world is that worm from? Often, worms you buy from worm farms belong to a species brought originally from China: the Chinese Jumping Worm. The jumping worm's jumps may be one factor in its escape from bait jars to the forests; another is that some anglers unthinkingly release their excess bait wherever they happen to be. Now, these non-native worms are eating the leaf litter that native millipedes and worms need to survive. The problem is at its worst in the dry southwestern part of the park, where millipedes require a good layer of leaf litter to survive in the drier microclimate. Many common bait fish sold at markets also are not native to this area and could threaten native fishes if introduced to Park waters.

To protect native species. Sometimes, anglers use animals they find stream-side for bait. But collecting or killing most animals in a national park is illegal. Banning bait removes the temptation to grab that rare salamander or lasso that mayfly.

You can read more about these invasive worms and how they are changing forest habitat for native millipedes in Issue 3: Resource Roundup: Inventory & Monitoring.

Non-native fish

From the late 1800s to 1975, local residents and Park biologists stocked the Smokies’ streams with trout—non-native brown and rainbow trout as well as native brook trout—so they would have plentiful fish to catch. They didn’t realize that brown and rainbow trout would out-compete brook trout in almost every stream, isolating populations in marginal streams at high elevations (often ones with declining pH). In some streams, brook trout populations dropped by as much as 90 percent.

In 1987, the Park began restoring the native brook trout. Biologists continue treating waters where rainbow and brown trout swim with an antibiotic called Antimycin to remove them. They also began studying brook trout genetics with park partners—the U.S. Fish and Wildlife Service, the University of Tennessee, Trout Unlimited, and Friends of the Smokies—to understand populations of brook trout and where they could restore fish for the best chance of recovery.

Read more about Brook Trout Research and Restoration in this issue’s NPS Profile: Return of the Native Brook Trout. To find out more about the fish themselves, go to the Park’s fish information page.

Return to Meet the Managers: Fisheries Management.

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