Flattened Musk Turtle

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).

Other Physical Features: ectothermic ; bilateral symmetry

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

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 )

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

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..

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

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

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).

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate)

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).

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).

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).

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).

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

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

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).

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".

The flattened musk turtle (Sternotherus depressus) is a critically endangered species of freshwater turtle in the family Kinosternidae. The species is endemic to the southern United States.