Fine-rayed pigtoe an endangered species

The fine-rayed pigtoe, a freshwater mussel found in the Little River, has been on the endangered species list since 1976.

People swim on the surface of the Little River and cast fishing lines but seldom consider the “living rocks” that may be burrowed below their toes.

About a dozen species of freshwater mussels can be found in the waterway, including the fine-rayed pigtoe, which has been on the federal endangered species list since 1976, and currently is up for a five-year review by the U.S. Fish and Wildlife Service.

At the time it was listed, there were only seven known populations, including one in the Little River, according to Anthony “Andy” Ford, an endangered species biologist with the service who is based in Cookeville, Tennessee.

“Mussels are one of the most imperiled fauna groups in North America,” he said.

Several things have disrupted their habitat, including dams, water pollution and erosion.

“They’re a great indicator species of water quality,” Ford said. “They’re the canary in the coal mine.”

“We don’t have massive, robust populations,” said Andrew Henderson, who is based in Ashville, North Carolina, and is the lead biologist for the endangered species listing and recovery of the fine-rayed pigtoe.

Riffles and runs

The fine-rayed pigtoe is likely to be in riffles, shallow areas of streams with fast-moving water, and runs, deeper but with little or no turbulence, and some pools.

“You have to know what to look for,” Henderson said. “They’re some of the most difficult to positively identify.”

The fine-rayed pigtoe is not the only mussel in the Little River or the only endangered mussel. Researchers from Virginia Polytechnic Institute in 2013 and 2014 also found the slabside pearlymussel, as well as several species considered imperiled, because their populations have declined dramatically.

The fine-rayed pigtoes are a dark chestnut color, and Henderson said the rays, which are greenish with yellow or yellow and brown are are subtle but visible. Most will be about 1 to 3 inches.

As they grow they become more elongated. Henderson said some in the Clinch River have grown to palm size.

They can burrow down into the substrate for about 6 inches and at other times may be on the surface, such as when the reproduce, from about mid-May through July.

Reproduction depends on host fish. During the larval stage the young are in stuck together in a packet that resembles the prey of shinners and minnows, which is how they become attached to the fish gills or fins to grow for a few weeks.

If they fall off in the wrong type of habitat, the young mussels won’t survive.

“There’s been a lot done with mussel propagation and reintegration in recent years,” Ford said. But the fine-rayed pigtoe is very sensitive, has a short breeding season and with the need for a host fish has not been a good candidate.


In 1918 a researcher reported identify 12 species of mussels in the Little River and five in Pistol Creek, A number of human actions took a toll on the mussels and their habitat over the past century.

In Tennessee freshwater mussels have been harvested in the past century to make buttons and to use in creating cultured pearls. Today anyone harvesting the mussels that may be collected must have a permit from the Tennessee Wildlife Resources Agency.

Dams also disrupted habitats, changing rivers into lakes and separating mussel populations so they can’t exchange genetic material.

U.S. Fish and Wildlife Service works with partners including other federal agencies, state natural resource offices, nongovernmental organizations, academic researchers and private landowners to improve natural conditions. “There’s a lot of people out their doing good conservation work,” Henderson said.

A number of small actions can add up to better water quality, such as building fences so cows don’t have direct access to rivers. When cattle can reach the banks, those banks can fail. “It’s not really safe for the cattle, and it’s not great for the critters,” Henderson explained.

Removing old dams, such as from mills no longer in service, can benefit those paddling canoes or kayaks as well as species such as the mussels.

How an dam operates can make a difference too. While a cold water discharge from a dam isn’t a problem for trout, it is for species such as mussels.The Tennessee Valley Authority has revisited how it operates many of its dams, according to Henderson.

Individuals can do their part to improve water quality too, he noted.

Planting riparian buffers, with grasses, shrubs and other plants prevents soil erosion and helps filter water.

Go light on herbicides and other chemicals, and don’t use creeks or storm drains as dumps.

Practice good erosion control to capture sediment, not only near banks of waterways but also along unpaved road ways and ditches.

The Virginia Tech researchers noted mussel densities declined downstream from where Ellejoy Creek joins with the Little River. They also cited a study from TVA in 2003 that estimated the Ellejoy Creek drainage area had the most extensive linear measurements of eroding stream bank and erosion from unpaved roads in the Little River watershed.

Another to watch

Another freshwater mussel closely related to the fine-rayed pigtoe, the Tennessee clubshell currently is under review for possible listing as an endangered species. The clubshell was relatively uncommon, Henderson said, it has become increasingly rare.

Education Reporter

Amy Beth earned her degree from West Virginia. She joined The Daily Times in 2016 on the education beat covering Alcoa, Maryville and Blount County school systems.

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