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Carolina heelsplitter mussels. Photo by Gary Peeples, USFWS.

Musseling back from near extinction

Only an estimated 154 Carolina heelsplitters remain in the wild. A shocking revelation for a species that’s been listed as endangered since 1993, but biologists with the U.S. Fish and Wildlife Service (Service) will not give up. Finding the Carolina heelsplitter, one of the most imperiled freshwater mussels in the Southeast, will bring delight to any biologist lucky enough to wade in its waters.

A dark colored mussel underwater in sandy substrate.
Carolina heelsplitter. Photo by USFWS.

Named for its ability to split the heel of anyone unlucky enough to plant a foot on it, the Carolina heelsplitter tops the list of rarities in the region. Lost from the record books since the 1800s, the species was rediscovered in 1987. But by that time, most populations had been eliminated from North Carolina and only a few remained in South Carolina—in geographic areas known as slate-belt stream systems. The Service listed the species as endangered in 1993 and designated critical habitat in 2002, spanning the states of North and South Carolina. Today, the heelsplitter’s distribution is fragmented, known only to exist in 11 populations in the Catawba, Pee Dee, Saluda, and Savannah river basins.

Threats to the Carolina heelsplitter are many. Like other freshwater mussel species, population declines are due to siltation from poor agriculture and silvicultural practices, conversion of forest land to impervious surface, road construction and maintenance, discharge of pollutants, habitat alterations…the list goes on. Persistent drought throughout the slate-belt stream systems, combined with the expansion of pine plantations in heelsplitter watersheds, has also dramatically lowered water flow and altered temperatures in streams where the Carolina heelsplitter occurs—a deadly mix of conditions for a species on the brink of extinction. The populations that are still hanging on contain very few individuals, further imperiling the species.

Fighting for the habitat

Bridges connect roads and highways, helping people reach their desired destinations. But in many instances, our system of roads and bridges contribute to the fragmentation of aquatic habitats, decimating species that depend on free-flowing creeks, streams, and rivers. The Carolina heelsplitter is highly sensitive to aquatic habitat degradation and totally dependent upon a host fish for movement of its genetic material.

Male Carolina heelsplitters release their sperm into the water column where it is siphoned in by the female heelsplitters. Once fertilization has taken place in the gills of the female heelsplitters, mature glochidia (larva) are released by the females where they must attach themselves to the gills and/or fins of unwitting fish hosts. As fish hosts travel up and down the creeks, streams, and rivers, the tiny juvenile mussels drop off in suitable habitat and contribute to the perpetuation of the species by spreading to new areas or simply being a part of the gene flow that must occur in order to keep populations healthy. This entire life cycle ceases if connectivity in their aquatic habitats is impaired or broken.

The USFWS logo next to the migratory bird treaty centennial logo
Old, dysfunctional culverts on Gills Creek (top) were replaced with a single bottomless arch culvert (bottom) to restore adequate flows. Photo by USFWS.

There are many different types of development projects that impact mussels; one of them being road development and maintenance. In fact, poor transportation planning in some areas has resulted in bridges that were constructed with culverts either undersized or not laid appropriately, impeding regular water flows, clogging up with debris, and sometimes, blowing out altogether during high water events. Restricted water flow can be a bad enough problem in and of itself but “blowouts” dump debris and sediment into the waterways, smothering aquatic life. And for the communities depending on a functional system of roads and bridges, this becomes their issue as well.

The Southeast Region’s aquatic habitat restoration team

In what may seem like a mix of oil and water, take an agency’s desire for better habitats for the species that they oversee and combine this with a county searching for answers on continuing transportation dilemmas. Throw in a few engineers and some determined Service employees, and what you end up with is a solution that benefits man and mussel.

The Southeast Region’s Aquatic Habitat Restoration Team is a unique cross-program partnership created to solve maintenance issues at wildlife refuges and fish hatcheries using the diverse set of skills of the Service’s workforce at a substantial cost savings to the government. This team specializes in heavy equipment operation, facilitation of dam removal, road crossing replacement, and stream restoration. From its early beginnings, the team has expanded its efforts across the region working with numerous Service biologists, as well as private landowners, federal and state agencies, and county governments.

Gills Creek

Gills Creek in Lancaster County is one of the few areas in South Carolina with designated critical habitat for the Carolina heelsplitter. It is also a watershed that has been heavily impacted by failed road crossings and flawed culvert designs. After one particularly damaging storm event in September 2012, the Service and officials from Lancaster County decided that better solutions were going to have to be employed for the Carolina heelsplitter to be lifted back from the brink of extinction. The solution would also help the county with their repetitive issue of blown out roads.

In May 2014, Service employees from across the Southeast, in partnership with Lancaster County officials and engineers, assembled for their first collaborative project on Gills Creek. Heavy equipment operators removed old, dysfunctional culverts and put in place a single bottomless arch culvert to restore adequate flow. Building on that success, the team assembled again in June 2015 for the second project on Gills Creek. Epic floods in October 2015 associated with Hurricane Joaquin tested the fortitude of these new bottomless arch culverts and proved their worth—no blown out bridges or roads! In July 2017, the Service will once again partner with Lancaster County in a third project in the Gills Creek watershed. When this project is completed, more than five miles of critical habitat for the heelsplitter will be restored, significantly aiding the recovery of this imperiled species.

Propagate, propagate!

Recovery cannot be achieved through habitat protection alone. Numbers of wild Carolina heelsplitters are so low that biologists can practically account for each and every last one of them. Dove-tailing on some successful propagation work undertaken in North Carolina, Service biologists began the painstaking work of assembling propagation facilities in South Carolina. Over the last several years, the Orangeburg Mussel Conservation Center (OMCC) was built at the Orangeburg National Fish Hatchery, and today it contains some of the most up-to-date mussel propagation equipment and manpower—staffed by some of the most inspiring biologists that the Service has “propagated.”

Two biologists crouching over buckets fed by plastic tubes.caro
Biologists measure and sort subadult heelsplitters. Photo by USFWS.

Growing mussels is a complex process. First, you have to actually find the mussel you so desperately want to propagate. Then, there is the small matter of harvesting the glochidia for propagating. Then the host fish, necessary for the maturation of glochidia, must be identified. After many years of research, the bluehead chub (Nocomis leptocephalus) has proven to be a successful host fish for the heelsplitter.

Once the host fish make their contribution to the life cycle of the mussel, the surviving juvenile mussels are meticulously tallied and cared for. To date, the OMCC has successfully propagated Carolina heelsplitters from three of the four basins across South Carolina with critical habitat for the species – the Catawba Basin, the Pee Dee Basin, and the Savannah basins – and cares for an estimated 915 heelsplitters in various stages of growth that await a future release.

Future for the species

Biologists are hopeful the heelsplitter population will begin to trend upward in 2017. Efforts to replace old, faulty culverts and plans to augment the low density populations in the wild with mussels raised at the OMCC will help jumpstart the heelsplitters long journey toward recovery. As American anthropologist Margaret Mead once said, “Never doubt that a small group of thoughtful, committed, citizens can change the world. Indeed, it is the only thing that ever has.”

Indeed, a thoughtful group of committed biologists working for the Service are improving the fortunes of the Carolina heelsplitter.


Jennifer Koches, a public affairs specialist in the Service’s Charleston Field Office, can be reached at or (843) 727-4707, ext. 214.

The mission of the U.S. Fish and Wildlife Service is working with others to conserve, protect, and enhance fish, wildlife, plants, and their habitats for the continuing benefit of the American people. For more information on our work and the people who can make it happen, visit Connect with the Service on Facebook, follow our tweets, watch the YouTube Channel and download photos from Flickr.

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