Smooth Softshell Apalone mutica - Special Concern

Family: Trionychidae

General Description: Smooth Softshells are named for the characteristically smooth, round, flat carapace. Unlike most other turtles, the bony elements of the carapace and plastron are reduced. The limbs are highly webbed and form a paddle to assist it while swimming in swift currents. Adult females have a carapace length of 7–14 inches (17.8–35.6 cm) and adult males have a carapace length of 5–7 inches (12–18 cm). The body color and carapace is tan to olive-gray in coloration. Juveniles will have a series of dark spots on the carapace that often fade away as individuals mature. The plastron is white and unmarked. On the head, a dark-bordered white line is present from behind the eye that runs to the neck. Unlike Spiny Softshells (Apalone spinifera), the Smooth Softshell lacks fleshy tubercles on their carapace and does not have a projection extending into the nostril from the nasal septum. In addition to being smaller than females, males have a proportionally larger, longer tail, with the cloaca being located at the tip of the tail.

Behavior: Smooth Softshells feeding primarily on aquatic insects, but will also eat fish, snails, mollusks, amphibians, and carrion. These turtles spend a fair amount of time basking on sandbars rather than on woody debris or logs. Turtles overwinter in the sandy substrates of the habitats they are found in.

Reproduction: Individuals breed in the early spring, with eggs being laid early June. Nests are made on bare sandy substrates, such as on sandbars, with little to no vegetation present. Eggs are white, leathery, and ovoid in shape. On average, females will lay 14 eggs that will hatch 8–12 weeks later in August. Sex of hatching turtles is determined genetically, rather than by temperature. Males reach sexual maturity in 4 years while females take up to 7 years.

Habitat: Smooth Softshells are highly aquatic turtles found primarily in large rivers and streams with moderate to fast currents, though they can also be found in reservoirs and oxbow lakes associated with these rivers. Typically, preferred habitats have sandy substrates.

Species Range: This species can be found throughout the Mississippi, Missouri, and Ohio river drainages, as well as large tributaries that are within these drainages. This species reaches as far north as North Dakota in the Missouri River drainage and Minnesota and Wisconsin in the Mississippi River drainage, east to Pennsylvania in the Ohio River drainage, and south to coastal Texas, Louisiana, Mississippi, and Alabama.

South Dakota Range: This species only occurs in free-flowing segments of the Missouri River and associated large tributaries.

South Dakota Status: The Smooth Softshell is listed on the South Dakota Natural Heritage Program. Any sightings of this species should be reported to South Dakota Game, Fish and Parks (report observation).

Account written by Drew R. Davis and Sydney R. Hancock

Distribution Map
Distribution map of Smooth Softshell (Apalone mutica)

County level distribution of this species in South Dakota. Map generated from data collected from voucher specimens and photographic records. See About for additional information.

Photographs
Smooth Softshell (Apalone mutica)
Smooth Softshell (Apalone mutica)