NASHVILLE, Tenn. (WKRN) — Six types of mussels that used to be found in various streams and rivers that run through Tennessee have officially been declared extinct.

The six mussels were among 21 different species of birds, fish, bats and other types of mussels across the U.S. that were delisted from the Endangered Species Act (ESA) due to extinction on Tuesday, Oct. 17, according to the U.S. Fish and Wildlife Service.

Like many of the newly delisted species, the mussels first received protection under the ESA in the 1970s and 1990s, and largely have not been seen since. In most cases, the FWS noted that the species “were in very low numbers or likely already extinct at the time of listing.”

“Federal protection came too late to reverse these species’ decline, and it’s a wake-up call on the importance of conserving imperiled species before it’s too late,” Service Director Martha Williams said in a news release announcing the decision.

Yellow blossom
Yellow-blossom pearly mussel (Courtesy: U.S. Fish and Wildlife Service)

Biologists have attributed the mussels’ demise to habitat fragmentation with the creation of structures for flood control, navigation, recreation and hydroelectric power production, as well as pollutants from construction, mining and farming that have affected water quality.

According to the FWS, freshwater mussels are important for filtering bacteria, algae and pollution from local waterways. In doing so, they absorb contaminants into their bodies, meaning if mussels are declining, the water could have a high level of pollutants.

The final rule to delist the species was published on Tuesday in the Federal Register and will become effective after 30 days, the FWS said. Below is more information about the species found in Tennessee that are now considered extinct.

Southern acornshell mussel

The southern acornshell was a round to oval shape mussel that was typically about 1.2 inches in length. The mussel was listed as endangered on March 17, 1993, primarily because of habitat modification, sedimentation and water quality degradation.

According to the FWS, runoff from fertilizers and pesticides can result in algal blooms and excessive growth of other aquatic vegetation, which ultimately kills mussels like the southern acornshell because of a lack of oxygen.

Historically, the species could be found in upper Coosa River tributaries and the Cahaba River in Alabama, Georgia and Tennessee. It was last collected in 1973, from the Conasauga River in Georgia and from Little Canoe Creek in Alabama.

When the species was listed in 1993, it was thought some were likely persisting in low numbers. However, many well-planned, comprehensive surveys by state and federal biologists have not been able to locate any live populations of southern acornshell mussels since the 1970s.

Upland combshell mussel

The upland combshell mussel was described as “rhomboidal to quadrate in shape” and was typically about 2.4 inches in length. The species was listed as endangered on March 17, 1993, because of habitat modification, sedimentation and water quality degradation.

The FWS said the upland combshell faced similar threats as the southern acornshell because both species were found in similar habitats. The upland combshell was historically found in shoals in rivers and large streams in the Black Warrior, Cahaba and Coosa River Systems.

As with most of the freshwater mussels found in the Mobile River Basin, it was found in stable sand, gravel and cobble in moderate to swift currents. Despite numerous surveys, there has been no evidence of the continued existence of the upland combshell for over three decades.

Green-blossom pearly mussel

The green-blossom was a medium-sized mussel with a lifespan up to 50 years. The shell outline was described as “irregularly ovate, elliptical, or obovate” and it could produce pearls. According to the FWS, the green-blossom was always extremely rare and never had a wide distribution.

It was listed as endangered on June 14, 1976. At the time, the single greatest factor contributing to the mussel’s decline was the alteration and destruction of a stream habitat due to impoundments of the Tennessee and Cumberland Rivers.

Stream impoundment kills off species like the green-blossom that are not capable of adapting to reduced flows and altered temperatures. Strip mining, coal washing, dredging, farming and road construction also likely severely affected the species, the FWS reported.

The last known collection of the green-blossom was 38 years ago, despite numerous surveys conducted over those years.

Tubercled-blossom pearly mussel

The tubercled-blossom was medium-sized, reaching about 3.6 inches in shell length, and could live as long as 50 years or more. The pearly mussel’s shell was irregularly egg-shaped or elliptical with distinct growth lines, a smooth, shiny outer surface and numerous green rays.

The species was listed as endangered on June 14, 1976, also because of significant habitat alteration, which the FWS said could be traced to impoundments for flood control, navigation, hydroelectric power production and recreation.

Unlike the green-blossom, the tubercled-blossom was historically relatively widespread. It was reported from the Tennessee River and tributary streams, as well as the Cumberland River. However, the last known collection of the species was more than 45 years ago.

Yellow-blossom pearly mussel

The yellow-blossom rarely was larger than 2.4 inches in length and had a shell surface marked by uneven growth lines. The shell was a shiny honey-yellow with several green rays and it had a bluish-white inner shell surface.

The species was listed as endangered on June 14, 1976, with impoundments in the Tennessee Valley and other regions severely affecting populations. A 1985 survey also documented numerous coal operations within the range of the mussel’s habitat and several polluted streams.

Although other federally listed mussels have been found by biologists within the last 50 years, there have been no signs of any living populations of yellow-blossom pearly mussels. The yellow-blossom was last sighted in the mid-1960s.

Turgid-blossom pearly mussel

The turgid-blossom was a small Cumberlandian-type mussel that was reported from the Ozarks. The species could live as long as 50 years or more, rarely exceeded 1.6 inches in shell length and had a shiny, yellowish-green color.

It was listed as endangered on June 14, 1976. The elimination of the turgid-blossom has been attributed to impoundments, barge canals, and other flow alteration structures that have impacted the species’ historical habitat.

The turgid-blossom used to be found in the Tennessee River and tributary streams, with additional records from the Cumberland River and the Ozark Mountain Region. The last known collection was a freshly dead specimen found in the Duck River in Tennessee in 1972.

Field notes associated with the collection indicate that it was found 100 yards from an old iron bridge, and water only one mile upstream was very muddy, presumably from dam construction.