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Rough pigtoe

Pleurobema plenum

Appearance

The rough pigtoe is a medium sized mussel 3 to 4 inches in length with an inflated, triangular shaped shell. Shell color ranges from dark to yellowish brown. Light green rays may be present on the shell of younger individuals. The color inside the shell varies from pearly white to pink.

Habitat

This species is endemic to the Ohio River system and is found in stable substrates composed of a mixture of relatively firm and clean gravel, sand, and silt. They are often associated with other riverine mussels that also prefer this type of habitat.

A shallow river surrounded by mature trees.
Rough pigtoe habitat in the Green River. Photo by Monte McGregor, Center Mollusk Conservation, Kentucky DFWR.

Diet

Mussels are filter feeders; they mainly eat phytoplankton, zooplankton, and bacteria suspended in the water. By drawing water inside their shells through a siphon, their gills filter out food and take in oxygen.

Historical range

The rough pigtoe had a broad distribution and was found in many of the major rivers and streams of the Mississippi River basin. Historical records for this species are known from the Tombighee River, Alabama River, Tennessee River, Holston River, French Broad River, Clinch River, Cumberland River, Ohio River, Allegheny River, Monogahela River, Kanawha River, Green River, Wabash River, Tippecanoe River, White River, Mississippi River, Illinois River, Neosho River, Ouachita River, St. Francis River, Meramec River, and James River. A detailed description of the historical records and their sources can be found in the Recovery Plan for this species.

A map depicting the Rough pigtoe's historical range including Kansas, Missouri, Illinois, Indiana, Ohio, Pennsylvania, Kentucky, West Virginia, Virginia, Arkansas, Tennessee, Mississippi and Alabama
historical range of the rough pigtoe. Map by USFWS.

Current range

The current distribution of the rough pigtoe includes six river systems:

  • The Clinch River in Virginia,
  • Portions of the Tennessee River in Tennessee and Alabama,
  • The Cumberland River in Tennessee,
  • The Green River and Barren River in Kentucky, and
  • The East Fork of the White River in Indiana.
  • Portions of the French Broad and Holston Rivers in Tennessee have experimental populations for this species. Overall, the rough pigtoe is extremely rare in most of its remaining distribution with the exception of the Green River. For a detailed description of the rough pigtoe’s current range please see our latest five-year review.

Counties where the species is present or believed to occur

  • Alabama: Colbert, Lauderdale, Lawrence, Limestone, Madison, Marshall and Morgan counties
  • Indiana: Lawrence and Martin counties
  • Kentucky: Butler, Edmonson, Green, Hart and Warren counties
  • Virginia: Buchanan, Dickenson, Lee, Norton, Russell, Scott, Smyth, Tazewell, Washington and Wise counties

Southeastern National Wildlife Refuges that provide habitat

Conservation challenges

Ongoing threats to the rough pigtoe include water quality degradation from point and non-point sources (e.g. runoff), particularly in tributaries that have limited capability to dilute and assimilate sewage, agricultural runoff, and other pollutants.

In addition, the species is affected by hydrologic and water quality alterations resulting from the operation of impoundments such as Green River Reservoir, Pickwick Lake, Wilson Lake, Guntersville Lake, and Cordell Hull Reservoir. The presence of impoundments may have ameliorated the effects of downstream siltation on the species, but these structures also control river discharges, and the many environmental parameters influenced by discharge, which may profoundly affect the ability of these populations to occupy or successfully reproduce in downstream habitats.

A variety of instream activities (e.g., sand and gravel dredging, road construction) continue to threaten rough pigtoe populations. Protecting these populations from the direct physical disturbance of such activities depends on accurately identifying the location of the populations, which is difficult with a cryptic species such as the rough pigtoe. The indirect effects of altering the streambed configuration may cause changes in previously suitable habitat some distance from the disturbance.

Coal, oil, and natural gas resources are present in some of the watersheds known to support rough pigtoe mussels, especially the Green, Barren, and Clinch Rivers. Exploration and extraction of these resources can result in increased siltation and an altered hydrograph and water quality, even at some distance from the mine or well field. Land-based development near occupied habitats, including residential development and agriculture, often results in loss of riparian habitat, increased stormwater runoff due to increased impervious surfaces, increased sedimentation due to loss of streamside vegetation, and subsequent degradation of stream banks.

Zebra mussels have continued to spread in North American waterways since their accidental introduction in the 1980s. Large zebra mussel populations in Lake St. Clair, the Detroit River, and Lake Erie appear to have eliminated most native mussels from the areas colonized, although the species may persist in refugia where habitat is less suitable for zebra mussels. Presently, zebra mussel populations do not appear to be having any negative impact on known rough pigtoe populations; however, this could change in the future. The presence of, or suitability of the habitat for, zebra mussels could also influence recovery actions to benefit this species, by limiting locations in which to start new populations and/or impacting newly started populations. It is also possible that drought, floods, or stochastic events play a role in the continuing existence of this species.

Recovery plan

Download the 1984 Recovery Plan.

The goal of the recovery plan is to maintain and restore viable populations of the rough pigtoe to a significant portion of its historical range and remove it from the endangered species list. This can be accomplished by protecting and enhancing existing habitat containing rough pigtoe populations, and establishing populations in river and corridors that historically contained rough pigtoes.

How you can help

Individuals can do a number of things to help protect mussels, such as:

  • Conserving water to allow more water to remain in streams.
  • Using pesticides responsibly, especially around streams and lakes, to prevent runoff into mussel habitats.
  • Controlling soil erosion by planting trees and plants to avoid runoff of sediments into freshwater areas.
  • Supporting practices for construction and maintenance of unpaved, rural dirt and gravel roads that minimize erosion and connectivity to our rivers and lakes.
  • Supporting and follow zebra mussel quarantine, inspection, and decontamination programs to prevent the spread of zebra mussels, an invasive species that competes with native mussels.

Subject matter experts

Designated critical habitat

No critical habitat is designated for this species.

Additional resources

Federal Register notices

The following Federal Register documents were automatically gathered by searching the Federal Register Official API with this species’ scientific name ordered by relevance. You can conduct your own search on the Federal Register website.

  • We're sorry but an error occurred. Visit the Federal Register to conduct your own search.

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