Sternotherus depressus (Family Kinosternidae) is a crevice-adapted species endemic to clear, clean streams and rivers of the upper Warrior River Basin, north-central Alabama. It is threatened by habitat alteration and degradation, disease, and possibly by collecting. The turtle is protected by United States federal and Alabama state law. Conservation measures should include research on life history, habitat use, demography, genetics of fragmented populations, and the effects of disease (if still present) on both individual turtles and affected populations. Historical locations, especially important sites sampled from 1981 to 2003, should be re-sampled and designated permanent monitoring sites. Local efforts to restore stream quality in the Warrior River Basin need to be undertaken, adjacent riparian habitats must be protected, laws and regulations should be enforced, and government agencies and non-governmental organizations should promote an understanding of the importance of biodiversity and endangered species management to residents and county officials.

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Unlike many aquatic turtles, this shy, secretive species rarely basks in the sunshine when healthy, instead showing a strong tendency towards crepuscular and nocturnal activity, particularly during summer (3). However, sick flattened musk turtles often bask in order to raise their body temperature, a phenomenon known as behavioural fever (4). Snails and clams are preferred food items, particularly the introduced Asian clam, but the diet also includes aquatic insects, arachnids, crayfish and the occasional dead fish (3) (6). Juveniles are apparently more active during the day than adults and rely more heavily on insects, although small snails are also consumed (3). Males mature at around four to six years of age, females at six to eight (3) (6). Females lay one to two clutches of eggs a year between May and early July (2) (3). Each clutch contains one to four eggs and is deposited in a shallow nest dug in a high sandy bank (3). Flattened musk turtles are long-lived, with a life span of 20 to 40 years (3). Juveniles are at risk from wading birds and possibly some predatory fish, while raccoons and possibly otters are thought to prey on adults and nests (3) (4). Large common snapping turtles are possible predators of both juveniles and adults (3).

As its common name suggests, this small freshwater turtle (3) has a distinctly flattened top shell (carapace), which is slightly serrated at the rear edge in juveniles, but becomes smooth with age (2) (4). The upper shell is yellowish-brown to dark brown with small, black spots and streaks and dark bordered seams, while the lower shell (plastron) is either pink or yellow (2) (5) (6). The head, legs and tail are olive-green with a network of fine black mottling (5) (6). All four feet are webbed and males have long, thick, spine-tipped tails (2) (6).

Sternotherus depressus inhabits a small range in the Black Warrior River system of Alabama.

The area of occupancy (AOO) and extent of occurrence (EOO) have not been quantified, but the EOO is at the order of 7,000 km² while an AOO of less than 500 linear km of streams and rivers is a realistic estimate.

These turtles are currently only found in the Black Warrior River watershed above the Bankhead Dam, in Alabama. The ten Alabama counties included in this range are Blount, Cullman, Etawah, Fayette, Jefferson, Lawrence, Marshall, Tuscaloosa, Walker and Winston.

Biogeographic Regions: nearctic (Native )

endemic to a single state or province

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Historically restricted to upper Black Warrior River system, northern Alabama, upstream from Fall Line; largest known population is in Sipsey Fork in north-central Alabama (Dodd 1988); USFWS considers populations unaffected by hybridization to be restricted presently to areas upstream from Bankhead Dam (USFWS 1987). Ernst et al. (1988) suggested that populations in west-central Alabama, previously regarded as intermediate between DEPRESSUS and MINOR (Mount 1975), are referable to DEPRESSUS.

Continent: North-America
Distribution: USA (N Alabama)  
Type locality: "Mulberry Fork of the Black Warrior River, 9 miles east of Jasper, Walker County, Alabama, near the bridge crossing of U.S. Highway 78".

Historic Range:
U.S.A. (AL)

USA. Restricted to the upper Warrior River Basin, north-central Alabama.          

Distribution of Sternotherus depressus in Alabama, USA. Red points = museum and literature occurrence records based on published records plus more recent and author’s data; green shading =  projected distribution based on GIS-defined hydrologic unit compartments (HUCs) constructed around verified localities and then adding HUCs that connect known point localities in the same watershed or physiographic region, and similar habitats and elevations as verified HUCs (Buhlmann et al., unpubl. data), and adjusted based on author’s data.

 

Restricted to the upper Black Warrior River system of west-central Alabama, U.S. (2) (6).

Sternotherus depressus ranges from about 3 to 4 inches (7.5 - 10 cm) in carapace length; record in 4.6 in (11.7 cm). When compared with other musk turtles, Sternotherus depressus has a carapace that is quite flattened. The top of the carapace is brown and the small plastron is either pinkish or yellowish-brown. The head and neck are greenish with a network of dark lines around them, and there are barbels located on the chin (Conant and Collins 1998).

Length: 11 cm

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

This turtle is mostly found in clear, shallow streams above the fall line. Rocky to sandy-bottomed streams are preferred (Ernst, Lovich, and Barbour 1994).

Aquatic Biomes: rivers and streams

Comments: Optimal habitat free-flowing creek or small river with pools about 1 m deep or more, hiding places among rocks, abundant mollusks, low silt load and deposits, moderate temperature; also impoundments with similar characteristics (Mount 1981). Preferred habitat seems to be clear, rock-bottomed to sandy, permanent streams above fall line (Ernst and Barbour 1989). Extensive sand deposits were major physical component of most high density sites (Ernst et al. 1989).

The flattened musk turtle is found in a variety of rivers, streams and in the shallow upper reaches of reservoirs, but its preferred habitat appears to be large, clear, free-flowing creeks or rivers. It inhabits areas with large flat rocks, moderately sandy bottoms and vegetated shallows, with alternating riffles and pools (2) (6) (4). The turtles wedge themselves in crevices and under large flat rocks, hence their flattened shells (4).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No 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.

The flattened musk turtle feeds underwater on invertebrates such as snails and mussels. Large adult musk turtles have expanded jaws for crushing mollusks.

Comments: Mollusks are the primary food, though other invertebrates also may be eaten (Mount 1975). Diet mainly clams (including the introduced Asiatic clam), snails, insects, crayfish, arachnids, and isopods; feces also sometimes contain seeds (Ernst and Barbour 1989, Marion et al. 1991).

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

Estimated Number of Occurrences: 1 - 5

Commonly parasitized by leeches (Placobdella parasitica) (Dodd 1988).

Comments: Active from April to October. Adults mainly nocturnal; juveniles more likely to be active by day but also more active with darkness (Ernst et al. 1989).

Females come out of the water and deposit their eggs in shallow nests dug into the ground near the stream. Each female chooses a different site. Clutch size appears small; two eggs are reported in one clutch. Eggs are oblong, about 32 mm long, with brittle shells. The incubation period is probably dependent on temperature and perhaps other physical factors, but ranges from 45 to 122 days. Once hatching begins the actual emergence from the egg takes anywhere from 12 hours to two days. The hatchling has a carapace length of about 26 mm. Growth to maturity may take four to six years for males, and six to eight years for females (Ernst, Lovich, and Barbour, 1994).

Lays 1-2 clutches of about 3 eggs in spring and summer. Males sexually mature in 4-6 years, females in 6-8 years (Mount 1981).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 1
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

These animals are sensitive to changes in streambed habitats, and especially to water quality. These musk turtles can only survive in pure waters. Sharp declines in recent decades have occurred due in part to an increase in pollution levels in their aquatic habitat. This is mainly due to coal strip mining. These turtles have also been collected in large numbers for the commercial pet trade. In February of 1986, at a Birmingham public hearing about the Fisheries and Wildlife Service's proposal to list the flattened musk turtle as "threatened" under the Endangered Species Act, representatives of the coal industry claimed that listing the turtle as 'threatened" could mean an end to coal mining in the area. But the U.S. Fish and Wildlife Service testified that coal mining would not be affected if the State and Federal strip-mining laws were obeyed. Strip miners are required to control discharges, and mining is barred within a certain distance of rivers. It is the lack of attention to these rules that has destroyed the flattened musk turtle's habitat as well as the valuable drinking water. Protecting the turtle would therefore also protect the quality of water for the citizens of Birmingham and northern Alabama. In June 1986 the proposal to list the Flattened Musk Turtle as threatened was accepted and became law. (Environmental Defense Fund, 1986)

US Federal List: threatened

IUCN Red List of Threatened Species: vulnerable

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G2 - Imperiled

Reasons: Small range in the Black Warrior River system, Alabama; threatened by overcollecting, disease, and habitat degradation from sedimentation and water pollution (in part related to coal mining); habitat fragmentation and related increased vulnerability to human-caused catastrophes and demographic accidents also appear to be problems.

Current Listing Status Summary

Status: Threatened
Date Listed: 06/11/1987
Lead Region:   Southeast Region (Region 4) 
Where Listed: Black Warrior R. system upstream from Bankhead Dam


Population detail:

Population location: Black Warrior R. system upstream from Bankhead Dam
Listing status: T

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

IUCN 2007 Red List: Vulnerable (VU B1+2c) (assessed 1996, needs updating); CITES: Not Listed; US ESA: Threatened.

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1).

Population

Population Trend

Global Short Term Trend: Decline of 10-30%

Comments: Has disappeared from more than half of former range; only 7% of probable historic range contains relatively healthy populations (Dodd 1990). Recent studies "indicate that population declines have continued, even at sites considered relatively pristine, as a result of insufficient recruitment and/or illegal collection" (Bailey and Guyer 1998). USFWS (1990) categorized the status as "unknown." See Ernst et al. (1989) for an extensive discussion of status.

Major Threats

Comments: Portions of habitat have been eliminated by impoundments, and agricultural, residential, and industrial development; threatened by overcollecting, disease, and habitat degradation from sedimentation and water pollution (in part related to coal mining) (USFWS 1987). Habitat fragmentation and related increased vulnerability to human-caused catastrophes and demographic accidents also appear to be problems (Dodd 1990). Sipsey Fork population declined in the mid-1980s, apparently affected by disease and/or commercial collecting (Dodd 1988); a modest reduction in survival over a relatively short time period resulted in a large decline in abundance from which recovery has not occurred; lack of recovery may stem from low reproductive potential, fragmented remaining habitats, collecting, and/or herbicide contamination (Fonnesbeck and Dodd 2003).

The flattened musk turtle is most seriously threatened by habitat degradation and fragmentation, and remaining populations are further threatened by disease, pollution and siltation of its habitat, and over-collection from the wild for the pet trade (2) (3) (7) (8). Pollution from mining, forestry, agricultural and industrial chemicals and residential sewage is thought to be responsible for the high levels of shell erosion and infections recently observed in this species, as well as reducing numbers of molluscs and other invertebrates on which the species feeds (2). Excessive sediment accumulation (siltation) also appears to be having a dramatic impact on this small turtle, possibly through smothering molluscs and other invertebrate food sources, altering the habitat where this turtle seeks food and cover, and accumulating heavy metals and chemical toxins (2) (3). In the 1970s and 80s, commercial collecting for the pet trade further reduced some populations, with large collections having been recorded and individuals advertised in several places for over 80 U.S. dollars each (2) (3) (4). It is also hard for flattened musk turtle populations to recover from any adverse changes, due to its slowness to mature and low reproductive rate (see 'Biology') (2).

Conservation Actions

A bill passed by the Alabama legislature in May 1984 prohibits the taking of this species from the wild and may be a deterrent to commercial overexploitation in the future (9). The flattened musk turtle is also protected as threatened under the US Endangered Species Act of 1973, as amended. It is therefore a nationally-recognised species of concern and is fully protected by law. In addition, a Federal Recovery Plan has been approved (2) (4).

This turtle is of no concern to fish management and is harmless to human interests.

The presence of this species is a good indication of the condition of the streams, as it requires clear, relatively unpolluted habitat.

Unfortunately, the Flattened Musk Turtle has had value in the pet trade, and has been heavily exploited for that reason in some parts of its small range..

Comments: Sometimes S. DEPRESSUS has been regarded as a subspecies of K. MINOR, with which DEPRESSUS has hybridized in some areas. MtDNA data indicate that S. DEPRESSUS is phylogenetically distinct from S. M. MINOR, S. M. PELTIFER, and all other kinosternid turtles in the southeastern United States (Walker and Avise 1998, Walker et al. 1998). See Ernst et al. (1988), Ernst and Barbour (1989), and Iverson (1991) for additional taxonomic information.

The genus Sternotherus was merged into the genus Kinosternon by Ernst and Barbour (1989) (based on protein electromorph data of Seidel et al. 1986). This change not adopted in subsequent taxonomic lists (King and Burke 1989, Collins 1990). However, Iverson (1991) evaluated protein and morphological data for kinosternine turtles and concluded that there presently exists no adequate basis for recognizing Sternotherus as a genus distinct from Kinosternon. Nevertheless, Ernst et al. (1994) treated Kinosternon and Sternotherus as distinct genera.