Raleigh Ecological Services Field Office
Conserving the Nature of America

Tar River spinymussel (Elliptio steinstansana)

Tar River spinymussels.  Photo by Chris Eads

Tar River spinymussels. Photo by Chris Eads.

Federal Status: Endangered, Listed July 29, 1985

Description: The Tar River spinymussel is one of only three freshwater mussels with spines in the world. The brownish shell is rhomboid-shaped, up to 2.4 inches (6 cm) long, with 0-6 spines on each valve. The shell is rather smooth and shiny, with concentric rings, and ends in a blunt point. Younger individuals are orange-brown with greenish rays streaking outward from the hinge area. Adults are darker with less distinct rays. One to three small thin ridges run on the interior surface of the shell from the beak cavity to the lower ventral area of the shell. The anterior half of the shell’s inner surface is salmon-colored, the posterior half is iridescent blue. Juveniles may have up to 12 spines, however, adults tend to lose their spines as they mature.Their method of reproduction is similar among freshwater mussel species. Males release sperm into the water column, and the sperm are taken in by the females through their siphons as they respire. The eggs are fertilized and develop within the females' gills into larvae (glochidia). The females release the glochidia that must then attach to the gills or fins of specific fish species. The glochida transform into juvenile mussels and drop off the fish onto the stream bottom.

Habitat: The Tar River spinymussel lives in relatively silt-free uncompacted gravel and/or coarse sand in fast-flowing, well oxygenated stream reaches. It is found in association with other mussels, but it is never very numerous. It feeds by syphoning and filtering small food particles that are suspended in the water.

Distribution: The Tar River spinymussel is endemic only to the Tar River and Neuse River systems in North Carolina. In the Tar River system, the species has been documented only from the mainstem of the Tar River, Shocco Creek, Fishing Creek, Little Fishing Creek, and Swift Creek. In the Neuse River system, the species has been documented only from the Little River. Based on the most recent survey data, the species may be extirpated from the mainstem of the Tar River (last observation was a single individual in 2000) and Shocco Creek (last and only record was a shell found in 1993). Only 1 individual was found during the most recent surveys in Swift Creek (2004 – 2005); only 16 individuals in Little Fishing Creek (2008 and 2009); only 4 individuals in Fishing Creek (2008 and 2009); and, only 3 individuals have been found during the most recent surveys (2006-2008) of the Little River (Neuse River basin) (one each in 2006, 2007, and 2008 in same general area of the river).

Threats: Based on available data, all surviving populations of the Tar River spinymussel are small to extremely small in size, highly fragmented and isolated from one another, and are in decline. The primary factors affecting the species and its habitat appear to be primarily stream impacts (sedimentation, bank instability, loss of instream habitat) associated with the loss of forest lands and forested riparian buffers, and poorly controlled stormwater runoff of silt and other pollutants from forestry and agricultural (livestock and row crop farming) activities, development activities, and road construction, operation, and maintenance. Pesticides were implicated in the largest known mortality event for Tar River spinymussel. In addition to the above, point source discharges continue to affect and threaten habitat quality in the Tar River, and Wake County, North Carolina has proposed a new water supply reservoir and wastewater discharge which threatens the Little River population of the species.

Neither the State of North Carolina nor the local governments with jurisdictions within the watersheds of streams supporting populations of the Tar River spinymussel, currently have regulations/ordinances that are adequate to protect the species from many of the adverse effects of agriculture, private forestry, and residential and commercial development activities (e.g., degradation or loss of riparian buffers; impacts to the streams’ hydrographs; stormwater runoff of sediments and other non-point source pollutants; wastewater discharges, etc.). The majority of the land use activities in watersheds of streams supporting the Tar River spinymussel are occurring without any federal nexus or in cases where a federal nexus has existed, many of the measures necessary for the protection of the spinymussel and its habitat are not within the permitting or funding federal agencies’ authority to implement. Water withdrawals are still largely unregulated in the areas where this species occurs, although the State is considering a water allocation program to address this deficiency. Also, recent studies indicate that current federal and state water quality standards for several pollutants commonly found in wastewater discharges and stormwater runoff are either not available (no criteria or standard derived) or likely not protective of freshwater mussels and current regulations controlling the discharge or runoff of these pollutants are not protective.

The genetic viability of the surviving populations remains a significant concern. All of the remaining populations of the Tar River spinymussel appear to be effectively isolated from one another by impoundments and long reaches of highly degraded habitat; and, the numbers of all of the surviving populations appear to be well below the level necessary to maintain a reproductively viable population. In addition, streams supporting populations of the Tar River spinymussel have been affected by severe - exceptional drought conditions which persisted from the fall of 2006 through the spring of 2009 – flow in reaches of several of the streams supporting the species was significantly reduced and in places completely dried up; the post-drought status of populations of the species is being assessed.


N.C. Natural Heritage Program. 2001. Guide to Federally Listed Endangered and Threatened Species of North Carolina: Tar River spinymussel. NC Department of Environment and Natural Resources, Raleigh, NC. Page 65.

U.S. Fish and Wildlife Service. 1992. Revised Tar Spinymussel Recovery Plan. Atlanta, GA. 34 pp.

U.S. Fish and Wildlife Service. 2009. Tar River spinymussel Recovery Action Plan. Asheville, NC.

Species Contact:

Sarah McRae, Fish and Wildlife Biologist, 919-856-4520 ext. 16


Last Updated: November 10, 2020