- Taxon: Fish
- Range: North Carolina, Tennessee, and Virginia
- Status: Proposed for Listing as a Threatened Species Under the Endangered Species Act; Proposed Section 4(d) Rule
In April 2010, the U.S. Fish and Wildlife Service (Service) was petitioned to list the sickle darter, a small fish native to the upper Tennessee River drainage in North Carolina, Tennessee, and Virginia. In 2011, the Service published a 90-day finding indicating listing may be warranted, and based on that finding, conducted a Species Status Assessment (SSA) for the fish. An SSA compiles the best scientific and commercial data available regarding the species’ biology and any factors influencing its viability. Based on the information provided in the peer-reviewed SSA, the Service is proposing to list the sickle darter as a threatened species throughout its historical range.
The Service is also proposing a 4(d) rule for the species. Using the flexibility provided under Section 4(d) of the Endangered Species Act (ESA), the Service can tailor take prohibitions to those that provide conservation benefits for the species. This targeted approach can reduce ESA conflicts by allowing some activities to continue that may benefit and not significantly harm the darter, while focusing efforts on the threats that slow the species’ recovery. These customized protections of the ESA minimize the regulatory burden while maximizing the likelihood of recovery for threatened species.
Sickle darters are small, slender-bodied fish, with elongated, pointed snouts. Their total maximum length is less than 5 inches. Body color is brown to olive above and white to pale below. A thin black stripe extends along the top of the body from the head to the rear of the second dorsal fin. Eight to 14 black blotches extend along each side, sometimes appearing fused and forming a black stripe with wavy margins. A narrow yellow stripe may be present on each side above the dark blotches. This stripe is most prominent in juveniles and small adults. Sickle darters also have a sickle-shaped bar, or “teardrop”, below the eye.
Multiple black specks typically cover the lower half of sickle darter’s bodies. The tail fin has a black spot at its base and a black bar extending from the spot to the underneath side of the tail fin. The first dorsal fin has a dusky or black margin, followed by a clear band, another dusky band, and sometimes, another narrow clear band at the base of the fin. The remaining fins are mostly clear with diffuse dark bands.
Sickle darters are typically found in slow flowing pools over rocky, sandy, or silty substrates in clear creeks or small rivers. In these habitats, the fish is commonly seen around boulders, woody debris piles, or beds of water willow. Sickle darters spend most of their time in the water column, often hovering a few inches above the stream or river bottom. The prominent black stripe or series of blotches along its sides are characteristic of darters living near vegetation in flowing pools. Spawning occurs in late winter (February-March), and the species has a maximum lifespan of 3-4 years.
Sickle darters feed primarily on larval mayflies and midges. Minor prey items include riffle beetles, caddisflies, dragonflies, and several other groups of aquatic invertebrates. Its long snout and large mouth likely aid its ability to capture and ingest larger mayflies.
The historical range (prior to 2005) of the sickle darter included nine tributary systems of the upper Tennessee River drainage in North Carolina, Tennessee, and Virginia: Emory River, Clinch River, Powell River, Little River, French Broad River, North Fork Holston River, Middle Fork Holston River, South Fork Holston River, and Watauga River. The greatest number of historical occurrence records are from the Emory River (Morgan County, Tennessee) and Little River (Blount County, Tennessee) systems.
Currently, the sickle darter is represented by six populations occupying portions of the Emory River system (Tennessee), Little River system (Tennessee), Sequatchie River system (Tennessee – discovered in 2014), the upper Clinch River system (Virginia), the North Fork Holston River system (Virginia), and the Middle Fork Holston River system (Virginia). Populations within the French Broad River (North Carolina and Tennessee), South Fork Holston River (Tennessee), Powell River (Tennessee), and Watauga River systems (Tennessee) have been lost.
Habitat loss and degradation
Habitat loss and degradation are the principal negative factors affecting sickle darter viability across its historical range. Siltation (excess sediments suspended or deposited in a stream), water quality degradation (pollution), and hydrologic alteration (impoundments) are the main stressors.
The sickle darter has a limited geographic range. Existing populations are localized and geographically isolated from one another due to impoundments and other forms of habitat degradation. Species that are restricted in range and population size are more likely to suffer loss of genetic diversity, decreasing their ability to adapt to environmental changes. This further reduces the fitness of individuals. The species’ long-term viability depends on the conservation of numerous local populations throughout its geographic range. These separate populations are essential for a species to recover and adapt to environmental change.
Climate change has the potential to increase the vulnerability of the sickle darter to random catastrophic events. The species’ early spawning period (February-March) makes it vulnerable to warming temperatures and higher flows – conditions that could interrupt or prevent successful spawning in a given year. An increase in both severity and variation in climate patterns is expected, with extreme floods, strong storms, and droughts becoming more common. Predicted impacts of climate change on fish include disruption to their physiology (such as temperature tolerance, dissolved oxygen needs, and metabolic rates), life history (such as timing of reproduction and growth rate), and distribution (range shifts and migration of new predators).
If the species is listed under the ESA, a recovery plan will be developed.
Partnerships, research and projects
Conservation Fisheries, INC (CFI) initiated propagation efforts for the sickle darter in 2015. Personnel from CFI collected adult male and female fish from the Little River in Tennessee. CFI was able to produce a total of 25 juvenile sickle darters from those efforts and released the juvenile fish in 2017. The propagation effort provided valuable information on the species’ reproduction and early life history and shows that there is potential for hatchery rearing and population restoration as a conservation tool in the future.
How you can help
- Support measures related to keeping our streams clean, such as land-use planning that maintains naturally forested river shore buffers and high water quality.
- Maintain native forests along streams and creeks. These forested buffers prevent the erosion of soil and sediments into the water after heavy rains, keeping the stream clear and clean.
- Do not dispose of toxic substances such as motor oil, pesticides, fertilizers, and other chemicals near creeks and streams. Always follow the instructions for chemical use, and properly dispose of any remaining material and the container.
- Keep livestock out of rivers and streams. Livestock can damage the stream banks by eating the bank vegetation and causing bank erosion. Livestock and their waste can also pollute the water.
- Watch for fish kills, illegal dumping of waste, unusual water color or smell, and other changes in the river’s condition. Report environmental emergencies to local authorities.
Subject matter experts
- Dr. Michael A. Floyd, U.S. Fish and Wildlife Service, Kentucky Ecological Services Field Office. Mike_Floyd@fws.gov, 502-695-0468 x 46102
Designated critical habitat
If the species is listed under the ESA, critical habitat may be designated.
Federal Register notices
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