Source: Endangered and Threatened Species of the Southeastern United
States (The Red Book) FWS Region 4 -- As of
(Percina (Imostoma) tanasi)
STATUS: On October 9, 1975, this species was officially classified in
the Federal Register as endangered. On July 5, 1984,
the snail darter was reclassified to threatened.
DESCRIPTION: The snail darter is a member of the subgenus Imostoma with
characteristics most similar to the closely
related stargazing darter (Percina uranida). Distinguishing characteristics of this fish are as follows: (1) modal number of anal
fin rays 12; (2) pectoral and pelvic fins short and rounded; and, nuptial males with pelvic fin tubercules confined to the four
median rays. The general body color is variable from brown to olive, sometimes blanched, with a dorsal saddle pattern often
strongly evident. Maximum size is approximately 89 millimeters or 3.5 inches.
REPRODUCTION AND DEVELOPMENT: Based on studies conducted in the Little
Tennessee River, the spawning
period is estimated to occur from mid-winter through mid-spring, and to take place in the shallower shoal areas over large,
smooth gravel. Water temperature during this period ranges from 5 to 16 degrees Centigrade. Multiple spawns are suspected.
Hatching takes place in about 18 to 2O days, with the larvae then drifting with the current to nursery areas farther downstream.
After a nursery period of 5 to 7 months, the juvenile darters begin to migrate back to the upstream spawning areas, where they
spend the remainder of the lives. About one-fourth of the darters reach sexual maturity in their first year, and the remainder
during the second year. The maximum lifespan seems to be 4 years. Food items of larger snail darters include both aquatic
insects and snails, but the snails form the bulk of the diet. The diet of snail darters below about 45 millimeters standard length
has not been studied.
RANGE AND POPULATION LEVEL: The snail darter was discovered August 1973
in the lower Little Tennessee River,
Loudon County, Tennessee, by Dr. David A. Etnier. After further collections and study, Dr. Etnier published his findings in
January 1976, indicating the snail darter to be a new species of percid fish. Before the construction of various impoundments,
this fish probably was abundant in the main channel of the Tennessee River and possibly ranged from the Holston, French
Broad, Lower Clinch, and Hiwassee Rivers, and downstream in the Tennessee drainage to northern Alabama.
Snail darter Critical Habitat in the Little Tennessee River was completely
eliminated in 1979 by the closure of Tellico Dam.
There is some evidence, however, that immediately downstream in the Tennessee River (headwater of Watts Bar Reservoir) a
viable population still remains in the 5- to 1O-mile stretch of riverine habitat below Fort Loudon Dam. Another population,
quite likely of natural origin, was discovered by Dr. Etnier in November 198O, in South Chickamauga Creek between creek
mile 5.6 in Tennessee (Hamilton County) and creek mile 19.3 in Georgia (Catoosa County). Subsequent 1981 and 1982
surveys in the Tennessee River drainage have revealed snail darters in Sewee Creek (Meigs County), and a few darters have
also been taken from the Tennessee River mainstream just below Chickamauga and Nickajack Dams, the Sequatchie River
(Tennessee), and Paint Rock River (Alabama). The remaining distribution has resulted from transplants. Since 1975, snail
darters have been transplanted in the following Tennessee Rivers: Hiwassee (Bradley and Polk Counties); Nolichucky
(Cocke/Greene Counties); Holston (Knox County); and Elk (Giles County). The Nolichucky transplant work was discontinued
early, and there has been no definite evidence of a surviving population. In 1988, snail darters were found in the French Broad
River upstream from its confluence with the Holston River. The population's status is unknown but occurences probably stem
from the Holston River transplants.
The population in the Little Tennessee River was variously estimated
at 5,OOO to 2O,OOO prior to the onset of detrimental
impacts from the construction of Tellico Dam. Adequate snail darter population estimates in upper Watts Bar Reservoir (main
channel Tennessee River below Tellico Dam) have not been made. Snail darters transplanted to the Hiwassee River in 1975
and 1976 had produced an estimated population of 2,5OO by 1979. Darters transplanted to the Nolichucky River in 1975
apparently did not survive. From December 1978 through November 6, 1979, a total of 1O4 darters from the Hiwassee and
427 from the Little Tennessee were transplanted to the Holston River near Mascot. In July 198O, a total of 425 snail darters,
previously removed from the Tellico project area were stocked into the Elk River. The South Chickamauga Creek population
is estimated at 2OO to 4OO. The Sewee Creek population has not been accurately assessed, but possibly numbers a few
thousand. The populations in the Paint Rock River and the Sequatchie River are undoubtedly very small as only a few
specimens have ever been taken.
HABITAT: In the Little Tennessee River, mature snail darters were known
only from portions of gravel shoals in the main
channel of the river. Fish were found in the swifter portions of shoals over clean gravel substrate in cool, low-turbidity water.
The juveniles utilized downstrean nursery sites located in the Tennessee River (Watts Bar Reservoir headwater). The snail
darters discovered in South Chickamauga Creek in 198O also utilize gravel shoal habitat, but the stream itself is much smaller,
has lower water quality in some portions, and gets much warmer in the summer. Sewee Creek, where a substantial snail darter
population was discovered in April 1991, apparently has good overall water quality and habitat similar to South Chickamauga
CRITICAL HABITAT: Critical habitat was designated in the Little Tennessee
River when the species was listed as
endangered in 1975. After a Federal law was passed exempting the proposed filling of Tellico Reservoir from Endangered
Species Act protection, the dam destroyed this darter's entire critical habitat area. When the species was downlisted to
threatened in 1984, the Little Tennessee River was officially removed from Endangered Species Act protection as snail darter
REASONS FOR CURRENT STATUS: The Little Tennessee River was the snail
darter's only known spawning habitat
when the species was listed as endangered. Although no populations now exist in the Little Tennessee River, the proposed and
subsequent construction of Telico Dam sparked reintroduction efforts and population surveys. New populations were either
discovered or started in the main stem Tennessee River and in six of its tributaries. After Dr. Etnier's discovery of the South
Chickamauga Creek population in November of 198O, and his later find of a single specimen in the lower Sequatchie River,
the Tennessee Valley Authority and the U.S. Fish and Wildlife Service initiated new studies in 1981 to better determine the
species' range. This research uncovered the Sewee Creek population and a few darters were also collected at several other
locations, including the Sequatchie and Paint Rock Rivers. Because several new populations had either been discovered or
established, the Snail Darter Recovery Team met with Fish and Wildlife Service biologists to recommend the following actions:
(1) Downlist the species from endangered to threatened; (2) Keep the species on the Federal list; and (3) Retain requirements
for a Federal permit to collect snail darters if downlisting to threatened occurs. All three recommendations were adopted, and
the species was downlisted to threatened in July 1984. Recovery team members voted not to delist the species because the
viability of its populations is still unknown.
MANAGEMENT AND PROTECTION: The Snail Darter Recovery Team recommends
that there should be at least five
separate viable populations to eliminate the threat of extinction. The transplant work conducted to date, along with the other
discovered populations, may be sufficient enough to eventually achieve this objective and provide a basis for completely
removing the snail darter from the Federal List of Endangered and Threatened Wildlife.
Etnier, David A. 1976. A New Percid Fish From The Little Tennessee River,
Tennessee. 44-Proc. Biol. Soc. Wash., Vol.
Hickman, Gary D., and Richard B. Fitz. 1978. A Report on the Ecology
and Conservation of the Snail Darter (Percina tanasi
Etnier) 1975-1977. Tennessee Valley Authority, Norris, Tennessee. 155 pp., app.
Starnes, Wayne C. 1977. The Ecology and Life History of the Endangered
Snail Darter, Percina (Imostoma) tanasi Etnier).
Ph.D. dissertation. Univ. Tennessee, Knoxville. 144 pp.