The snail darter, Percina tanasi, a small, extremely local freshwater fish of the family Percidae (perches and darters), was discovered in the Tennesee River in 1973, at the same time as construction of the nearby Tellico Dam. This darter was declared an endangered species in 1975 under the Endangered Species Act (ESA) of 1973, and became an icon for both the conservationist movement and anti-environmentalists as concerns that the Tellico dam would extirpate the species by destroying its only known habitat delayed dam construction for two years. During these years legal controversy ensued and the case made it to the Supreme Court, which ruled to uphold the ESA protection and close down the dam. As a result, congress amended the ESA to allow a subsequent committee (the “God Committee”, so called for its potential to command the extinction of a species) to exempt certain species from protection when economically unviable. However this committee also voted to uphold the darter’s protection. Finally congress passed an amendment excluding the Tellico dam from the ESA and the almost-completed dam project was allowed to proceed; it was completed in 1979. In 1975 snail darters were introduced into four eastern Tennessee river systems; the 710 transplants into the Hiwasssee River successfully established populations which became robust enough to upgrade the snail darters’ status to “threatened” in 1984. The IUCN assessed their status as “vulnerable” in 1996.

The snail darter is named for its dietary preference for aquatic snails, which make up the majority of this fish’s diet, although it also eats other small invertebrates. A short-lived species, they live about four years in captivity, and grow up to about 9 cm long. Snail darters spawn in rocky shoals. The eggs rest on gravel bottoms until they hatch about 20 days later, and the young drift downstream, later returning to the shoals to spawn as adults.

(Fuller and Neilson 2012; Hall 1999; IUCN 2011; Wikipedia 2011; Wikipedia 2012)

Occurs in gravel and sand runs of medium-sized rivers (Ref. 5723, 10294); also found in creeks (Ref. 10294). Feeds on small pleurocerid river snails, mostly Leptoxis and Lithasia, as well as some physid snails and limpets; also consumes caddisfly larvae (Glossosoma, Hydropsyche, Brachycentrus), midge and blackfly larvae, and a few mayfly nymphs (Ref. 10294).

Once limited to the Tennessee River and tributaries, the darter now also lives in connected reservoirs. In 1975 and 1976, a population was transplanted to the Hiwassee River, and is doing well.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Range includes the upper Tennessee River system in Tennessee, northern Alabama, and northern Georgia.

Current range (Tennessee, unless otherwise indicated): Tennessee River (reaches below the confluence of the Little Tennessee River, below Watts Bar Dam, below Nickajack Dam, and below Chickamauga Dam); South Chickamauga Creek, Hamilton County, and Catoosa County, Georgia; lower Sequatchie River, Marion County (may be extirpated; L. Barclay, Supervisor, Tennessee Field Office, U.S. Fish and Wildlife Service, pers. comm., October 6, 2005); lower Big Sewee Creek, Meigs County; lower French Broad River, Sevier County (evidently colonized from the Holston River); lower Holston River, Blount County (introduced from the Hiwassee and Little Tennessee rivers in 1978-1979); Little River, Blount County (colonized from the Holston River); lower Paint Rock River, Alabama; lower Hiwassee River, Polk County (introduced in 1975-1976) (Etnier and Starnes 1993, Boschung and Mayden 2004). A single snail darter was found in the Ocoee River in 1993 probably was a disperser from the Hiwassee River population. Snail darters were introduced in the Nolichucky and Elk rivers, but these streams do not contain extant populations. Occurrences in Tennessee reservoirs (Watts Bar in Louden County, Nickajack in Hamilton County, and Guntersville in Marion County) probably represent strays from tributary spawning areas.

Historic Range:
U.S.A. (AL, GA, TN)

North America: upper Tennessee River drainage of eastern Tennessee and northern Georgia in the USA.

Length: 8 cm

9.0 cm TL (male/unsexed; (Ref. 5723)); max. reported age: 4 years (Ref. 12193)

Paratype for Percina tanasi Etnier
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Collector(s): D. Etnier & et al.
Year Collected: 1973
Locality: Little Tennessee River At Coytee Spring, River Mile 7, Louden Co., Tenn., Louden County, Tennessee, United States, North America

Paratype for Percina tanasi Etnier
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Collector(s): D. Etnier & et al.
Year Collected: 1974
Locality: Little Tennessee River At Coytee Spring, River Mile 7, Louden Co., Tenn., Louden County, Tennessee, United States, North America

Systems

• Freshwater

Moderately flowing, vegetated streams with sandy bottoms and wide shoals for spawning.

Aquatic Biomes: rivers and streams

Habitat Type: Freshwater

Comments: Adults and spawning individuals inhabit sand and gravel shoals of moderately flowing, vegetated, large creeks and river; also in deeper portions of rivers and reservoirs where current is present (Etnier and Starnes 1993, Boschung and Mayden 2004). Young occur in slackwater habitats, including the deeper portions of rivers and reservoirs (Boschung and Mayden 2004). Individuals often burrow into substate (Etnier and Starnes 1993, Boschung and Mayden 2004).

benthopelagic; freshwater

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Larvae drift several kilometers downstream, and juveniles apparently migrate upstream in spring (Kuehne and Barbour 1983). Juveniles occupy slackwater habitats and migrate upstream to shoals by age of 3-4 months (Page 1983).

The snail darter eats small invertebrates, with aquatic snails making up about 60 percent of the darter's food, with some variation among seasons.

Comments: Eats mainly pleurocerid river snails, plus some physid snails and limpets; also immature insects, including caddisflies, midge larvae, and blackfly larvae, and a few mayfly nymphs (Etnier and Starnes 1993).

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 6 - 20

Comments: This species is represented by several (but fewer than 10) extant populations.

2500 - 10,000 individuals

Comments: Total adult population size is unknown but appears to be at least several thousand. The introduced population in the Hiwassee River consisted of around 2,500 individuals in the early 1990s (Etnier and Starnes 1993); this population was regarded as relatively abundant in 2004 (USFWS 2004). The populations in the Little River, Holston River, and Frnech Broad River were relatively abundant in 2004 (USFWS 2004; Shute and Saylor, in Mirarchi et al. 2004).

Density of 6-10/100 sq m of shoal habitat (Kuehne and Barbour 1983).

Average lifespan

Status: captivity: 4 years.

Between January and mid-March, adult snail darters spawn on river shoals. Eggs deposited in gravel or on rocks hatch in 15 to 20 days.

Spawns from February to about mid-April. Eggs hatch in 15-20 days (15 days at 12.5 C). Age range of breeding females is 1-3 years (Bart and Page 1992). A few may survive into a fourth year.

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There is 1 barcode sequence available from BOLD and GenBank.   Below is the sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen.  Other sequences that do not yet meet barcode criteria may also be available.
 

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Species: 1
Species With Barcodes: 1

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Originally classified as Endangered on October 9, 1975. Reclassified as Threatened on July 5, 1984. A number of new populations have been found, increasing the number of known individuals.

IUCN Red List of Threatened Species: vulnerable

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G2 - Imperiled

Reasons: Upper Tennessee River system, Tennessee, northern Alabama, and northern Georgia; less than 10 occurrences, and few of these represent robust populations; range is fragmented by impoundments; distribution and abundance have increased since the 1970s as a result of introductions and subsequent population expansion; species receives considerable management attention.

Current Listing Status Summary

Status: Threatened
Date Listed: 11/10/1975
Lead Region:   Southeast Region (Region 4) 
Where Listed:


Population detail:

Population location: entire
Listing status: T

For most current information and documents related to the conservation status and management of Percina tanasi , see its USFWS Species Profile

Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable

Comments: Impoundments have fragmented much of the range. Some populations are small and thus vulnerable to extirpation from localized events.

Threats to the continued existence of this species include agricultural development, environmental contamination and pollution, pesticides, channel modification, habitat inundation, and siltation (USFWS).

Challenges facing snail darters in the lower French Broad River include residential development, nonpoint source pollution, contamination from the Little Pigeon River, excessive aquatic macrophytes, sand dredging, and, potentially, exotic fish species (Scott 2000).

Vulnerable (VU) (D2)

Biological Research Needs: A critical research need in conserving the population in the lower French Broad River is determination of the darter's early life history (Scott 2000).

Global Protection: Unknown whether any occurrences are appropriately protected and managed

Needs: All known occurrences need protection. See recovery plan (USFWS 1983).

The snail darter case caused the Tellico Dam project to be halted. In response, Congress amended the Endangered Species Act to include a "God Squad", which could overrule protecting a species under enormous economic sacrifice. The committee got its name because it can play "God" and allow species to go extinct for economic reasons.

By traditional economics, the snail darter has no significant positive economic importance. However, when listed as an Endangered Species in 1975, it was the focus of a Supreme Court case that set the precedent for protecting endangered species, regardless of cost.