Flattened Musk Turtle
FLATTENED MUSK TURTLE
Photo Credit: U.S. Geological Survey
Department of Interior/USGS
SCIENTIFIC NAME: Sternotherus depressus (Tinkle and Webb)
OTHER NAMES: None.
DESCRIPTION: A small (rarely >11.0 cm [4.3 in.] carapace length) freshwater turtle. Carapace yellow brown to dark brown with small, black spots or streaks; relatively flattened on dorsum. Plastron pink to yellowish brown, and anterior lobe somewhat flexible. Head moderately wide, olive colored with fine dark spots or blotches; may be somewhat enlarged in older adults. Two pairs of barbels on chin. Limbs and tail generally brown. Neck may have a longitudinal striping pattern, but stripes narrower and not as prominent as in the stripe-necked musk turtle (Ernst et al. 1994).
DISTRIBUTION: Endemic to Alabama, and restricted to Black Warrior River system in west-central Alabama.
HABITAT: Medium-sized creeks to larger streams and even impoundments. Optimal stream habitat consists of a drainage at least 80.5 square kilometers (50 square miles); alternating pools and riffles, with pools at least 1.0-1.5 meters (3-4.5 feet) deep; an abundance of submerged boulders and rocks, with crevices; an abundant molluscan and benthic invertebrate fauna; a low silt load; and clean water (Mount 1981a). Streams with a predominant sandy substrate also suitable as long as adequate boulder and crevice refugia present (Ernst et al. 1989).
LIFE HISTORY AND ECOLOGY: A shy and secretive bottom dweller that seldom basks. Adults show a strong preference for crepuscular and nocturnal activity, especially during summer. Juveniles apparently more active during the day than adults. Males have a larger home range and are more active than females, but most adults, male or female, remain within 20-30 meters (60-90 feet) of any one location during a season (Dodd 1988a). Snails and clams are primary food items for adults. Introduced Asian clam is primary bivalve taken (Marion et al. 1991). Benthic insects, crayfish, and an occasional dead fish also consumed. Juveniles eat small snails, but apparently rely more on insects than adults (Tinkle 1958). A strong relationship between the abundance of food items at a site and population densities exists (Bailey and Guyer 1988). Males reach sexual maturity in four to six years (at 6.0-6.5 cm [2.4-2.6 in.] carapace length); females, in six to eight years (at 7.0-7.5 cm [2.75-2.95 in.] carapace length). Females lay two clutches of eggs per year (May and mid-June through early July), with clutch sizes ranging from one to four eggs (ave. 4.2 eggs per year) (Close 1982). Females deposit eggs in shallow nests dug in high sandy banks, or at edge of surrounding riparian zone. As juveniles, preyed upon by wading birds and, possibly, some predatory fish species. Raccoons likely the predominant predator on adults. Large common snapping turtles are possible predators on both juveniles and adults. Relatively long-lived, with life spans of 20 to 40 years.
BASIS FOR STATUS CLASSIFICATION: Studies over the last three decades have indicated that the species is no longer present, or has significantly reduced population levels, over the majority of historic geographic distribution (Mount 1981, Dodd 1988, Ernst et al. 1989). Only a small portion of former distribution currently contains relatively healthy populations; those are fragmented by extensive areas of unsuitable habitat (Dodd 1990). In some areas where present, recruitment appears low. Reduction in populations has resulted primarily from poor water quality and excessive sedimentation caused by several factors. Historically, strip mining for coal and industrial and municipal pollution eliminated or severely impacted many populations. Forestry practices and agriculture, especially in the eastern portion of distribution, also contributed significantly to increased siltation in some streams (Mount 1981). Although exact mechanism unknown, there is a strong correlation between high siltation levels and population declines (Ernst et al. 1989). Excessive sediment accumulations may contain toxins or may smother invertebrate food sources. In more recent years, commercial collecting for the pet trade, and an unknown disease, further reduced some populations (USFWS 1987a). Impoundments, which flooded many miles of prime stream habitat, also were a significant factor in the historical decline of the species. However, recent and on-going studies in Lewis Smith Reservoir conducted by the authors indicate that some reservoir sites with low sediment accumulations, good water quality, and adequate refugia have apparent healthy, reproducing populations of at least low to moderate densities. Listed as threatened by the U.S. Fish and Wildlife Service in 1987.
Authors: Ken R. Marion and Mark A. Bailey
US Fish and Wildlife Service Fact Sheet