Overview

Distribution

endemic to a single nation

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National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: Gulf Coast from western Florida to eastern Texas, north to eastern New Mexico, southern South Dakota, Wisconsin, and northwestern Pennsylvania.

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Range Description

Apalone mutica inhabits the greater Mississippi basin from Louisiana up to North Dakota, Minnesota and western Pennsylvania, as well as the Colorado, Brazos, Sabine, and Pearl, Alabama and Escambia river systems (Webb 1973, Iverson 1992).

Apalone mutica mutica
: Mississippi basin, and western rivers to central Texas;

Apalone mutica calvata
: Pearl, Alabama and Escambia river systems.
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Geographic Range

Smooth softshell turtles, Apalone mutica, are native to temperate areas of North America, ranging throughout the central and south-central United States (Oldfield and Moriarty 1994, Ernst and Lovich 2009). Their range extends from Pennsylvania to New Mexico and south to the Florida panhandle. This species is thought to have been extirpated from Pennsylvania (Hulse et al. 2001). Smooth softshell turtles are believed to have occurred in North America since the Cretaceous Period (Quammen 1992), although this is not yet supported by fossil evidence (Ernst and Lovich 2009).

Smooth softshell turtles have also been introduced to France.

Two subspecies of smooth softshell turtles have been identified. Midland smooth softshells, Apalone mutica mutica, are found throughout the central United States, while Gulf coast smooth softshells, Apalone mutica calvata, range from Louisiana to the panhandle of Florida (Ernst and Lovich 2009).

Biogeographic Regions: nearctic (Native ); palearctic (Introduced )

  • Ernst, C., R. Barbour, J. Lovich. 1994. Turtles of the United States and Canada. Washington D.C.: Smithsonian Institution Press.
  • Ernst, C., J. Lovich. 2009. Turtles of the United States and Canada. Baltimore, Maryland: The John Hopkins University Press.
  • Hulse, A., C. McCoy, E. Censky. 2001. Amphibians and reptiles of Pennsylvania and the Northeast. Ithaca, New York: Cornell University Press.
  • Oldfield, B., J. Moriarty. 1994. Amphibians & Reptiles Native to Minnesota. Minneapolis, Minnesota: University of Minnesota Press.
  • Quammen, R. 1992. A latest Cretaceous (Maestrictian) lower vertebrate faunule from the Hell Creek Fromation of North Dakota. Proceedings of the North Dakota Academy of Science, 46: 41.
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Continent: North-America
Distribution: USA (Ohio, Minnesota, S North Dakota, South Dakota, E/S Nebraska, Kansas, Oklahoma, N/E Texas, Mississippi, Missouri, Iowa, Arkansas, Louisiana, Illinois, Wisconsin, Indiana, Kentucky, Tennessee, Alabama, W Florida Panhandle, E New Mexico; Considered extirpated in W Pennsylvania)  calvata: Mississippi;
Type locality: Pearl River, Roses Bluff, 14 mi E Jackson, Rankin County, Mississippi; W. F. Childers; August 25, 1952.  
Type locality: "Newharmony, sur le Wabash" (=New Harmony, Wabash River), Posey County, Indiana, USA
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Physical Description

Morphology

Physical Description

Smooth softshell turtles are medium to large freshwater turtles. This species displays sexual dimorphism, and females are generally larger than males. Females have a carapace length ranging from 16.5 to 35.6 cm and males from 11.5 to 26.6 cm (Oldfield and Moriarty 1994; Ernst and Lovich 2009). Photographs of this turtle are available at the Minnesota Department of Natural Resources website.

As with other softshells, smooth softshell turtles have a carapace that is covered by skin instead of the hard scutes commonly observed in other turtle species (Oldfield and Moriarty 1994; Ernst and Lovich 2009). The carapace is ovoid and lacks spines on the front edge. Smooth softshell turtles have a tubular snout with round nostrils that are usually positioned inferior, and they lack a septal ridge (Oldfield and Moriarty 1994; Ernst and Lovich 2009).

Adult smooth softshell turtles generally have a carapace coloring ranging from olive to orange (Ernst and Lovich 2009). Females typically have a tan or brown carapace, while males have a brown or gray carapace (Oldfield and Moriarty 1994). Both sexes have dark markings (spots, streaks, or blotches) on their carapace, although females typically have a blotchier pattern. The plastron is light (white or gray) with no markings, and the underlying bones are visible (Oldfield and Moriarty 1994; Ernst and Lovich 2009). Dorsal coloration of an individual's head, limbs, and tail are similar to that of its carapace. A cream or orange line bordered in black extends from the back of each eye to the neck (Oldfield and Moriarty 1994; Ernst and Lovich 2009).

Juvenile smooth softshell turtles do not differ in coloration from adults. Hatchlings have a brown or olive carapace with many markings on the carapace (Oldfield and Moriarty 1994; Ernst and Lovich 2009).

Male smooth softshell turtles have thicker tails than females, a trait commonly observed in turtle species (Ernst and Lovich 2009). In males, the anal vent is located near the tip of the tail, while in females, the anal vent is usually located near the edge of or under the carapace (Ernst and Lovich 2009). As with other species of turtles, female smooth softshells have longer hind claws than males, which have longer foreclaws than females (Ernst and Lovich 2009).

Two subspecies of smooth softshell turtles have been identified, midland smooth softshell turtles, Apalone mutica mutica, and Gulf coast smooth softshell turtles Apalone mutica calvata. In addition to habitat, juvenile color patterns help to distinguish the two subspecies in the field.

Smooth softshell turtles are the most aquatic of all North American softshells (Ernst and Lovich 2009). Their aquatic nature is made possible by a variety of behavioral and morphological adaptations. The skin covering the shell causes a high rate of water exchange (Stone and Iverson 1999). Water exchange in freshwater is typically 6.3 mL/100g wet BM/hour (Ernst and Lovich 2009). The lining of the cloaca and pharynx enables uptake of oxygen from the water (Oldfield and Moriarty 1994). Furthermore, the surface of their shell and skin is cutaneous, increasing the permeability of gases and water (Stone and Iverson 1999). For instance, smooth softshell turtles lose about 64% of respiration-produced carbon dioxide through their skin (Jackson et al. 1976). Their long neck and snout contribute to the ability to remain submerged for extensive periods of time (Oldfield and Moriarty 1994).

Smooth softshell turtles are mostly easily confused with spiny softshells, Apalone spinifera. The two species, however, can be distinguished by examining the carapace. Spiny softshells have spines along the front edge of their carapace, and the carapace usually has a sandpaper texture. Smooth softshells lack these characteristics. Spiny softshells, as with most softshell turtles, also have a septal ridge in the nose. However, smooth softshells lack a septal ridge. Distinguishing features of other softshell species include heavily marked limbs and spines on the carapace (Ernst and Lovich 2009).

Range length: males 11.5 cm; females 16.5 to males 26.6 cm; females 35.6 cm.

Sexual Dimorphism: female larger; sexes colored or patterned differently

  • Jackson, D., J. Allen, P. Strupp. 1976. The contribution of non-pulmonary surfaces to CO2 loss in 6 species of turtles at 20 C. Comparative Biochemistry and Physiology, 55A: 243-246.
  • Minnesota Department of Natural Resources, 2011. "Apalone mutica" (On-line). Minnesota Department of Natural Resources. Accessed April 03, 2011 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=ARAAG01020.
  • Stone, P., J. Iverson. 1999. Cutaneous surface area in freshwater turtles. Chelonian Conservation and Biology, 3: 512-515.
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Size

Length: 36 cm

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Type Information

Paratype for Apalone mutica calvata
Catalog Number: USNM 7655
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: ; Juvenile
Preparation: Ethanol
Locality: Monticello, Lawrence, Mississippi, United States, North America
  • Paratype: Webb, R. G. 1959. Univ. Kansas Publ., Mus. Nat. Hist. 11 (9).
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Ecology

Habitat

Comments: Large rivers and streams; in some areas also found in lakes, impoundments, and shallow bogs (Ernst and Barbour 1972). Usually in water with sandy or mud bottom and few aquatic plants. Often basks on sand bars and mudflats at edge of water. Eggs are laid in nests dug in high open sandbars and banks close to water, usually within 90 m of water (Fitch and Plummer 1975).

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Habitat and Ecology

Habitat and Ecology
Apalone mutica typically occur in medium-sized to large rivers with moderate to fast currents, but also occur in standing water bodies like lakes, ponds and marshes as long as these are connected to the river at least during floods. Soft bottoms are preferred, and accessible sandbanks must be present. Smooth Softshells are preferentially carnivorous omnivores, feeding mainly on insects but also taking other kinds of animal food as well as plant seeds and fruits.

Males reach 27 cm carapace length (CL); females 36 cm CL. Maturity is reached at four years in males, nine years in females; size at maturity is apparently unknown. Longevity probably exceeds 20 years. Generation time has not been calculated.

Females produce two to three clutches of about 14 (1–33) eggs. Incubation takes about 63 (44–82) days. Hatchlings measure 30–37 mm (reviews by Moler 2006, Ernst and Lovich 2009).

Systems
  • Terrestrial
  • Freshwater
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Smooth softshell turtles are typically found along major riverine systems such as the Ohio, Missouri, and Mississippi rivers (Oldfield and Moriarty 1994). They prefer large rivers and streams with medium to fast currents (Bodie et al. 2000). Within river systems, smooth softshell turtles had highest populations in the open side channels and main channels of the Mississippi and Ohio Rivers in southern Illinois (Barko and Briggler 2006). Despite their preference for riverine systems, smooth softshell turtles have also been found in lakes, bogs, ponds, and drainage ditches (Ernst and Barbour 1989; Oldfield and Moriarty 1994; Ernst and Lovich 2009). They generally prefer areas of sandy or mucky bottoms with little aquatic vegetation, and they avoid aquatic systems with a rocky substrate.

Smooth softshell turtles have microhabitat preferences within the Kansas River in Kansas (Plummer 1977). Males were observed more frequently than subadult and adult females in shallow depths along the river. Hatchlings also preferred shallow areas along the river, most likely to avoid larger aquatic predators.

Of the subspecies of smooth softshell turtles, Gulf coast smooth softshells, Apalone mutica calvata, have been found only in riverine and stream systems, while midland smooth softshells, Apalone mutica mutica, have also been observed inhabiting lakes, bogs, drainage ditches, and ponds (Oldfield and Moriarty 1994; Ernst and Lovich 2009).

Range elevation: 1300 (high) m.

Habitat Regions: temperate ; freshwater

Aquatic Biomes: lakes and ponds; rivers and streams

Wetlands: marsh ; swamp ; bog

Other Habitat Features: riparian

  • Barko, V., J. Briggler. 2006. Midland smooth softshell (Apalone mutica) and spiny softshell (Apalone spinifera) turtles in the middle Mississippi River: Habitat associations, population structure, and implications for conservation. Chelonian Conservation and Biology, 5: 225-231.
  • Bodie, J., R. Semlitsch, R. Renken. 2000. Diversity and structure of turtle assemblages: Associations with wetland characters across floodplain landscape. Ecography, 23: 444-456.
  • Plummer, M. 1977. Activity, habitat, and population structure in the turtle, Trionyx muticus. Copeia, 3: 431-440.
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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

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.

In a Kansas river (Plummer and Shirer 1975), individual smooth softshells moved 2-4 km upstream or downstream in one day, and they were often recaptured in areas extending 2-3 river km. An adult female moved 7.8 km upstream in two days. Only one long-distance movement exceeded 8 km. Mean short-term home range length was 1.2 km (range up to about 2.4 km in adult females, 0.5 km (up to about 1.1 km) in males, but both sexes made long but brief movements out of their home ranges, and sometimes they shifted home range location during a single season.

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Trophic Strategy

Comments: Eats insects, crayfish, snails, worms, fish, and amphibians; males forage more along shore than do females (Collins 1982). Also reported to eat fruits and cottonwood seeds.

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Food Habits

Smooth softshell turtles are carnivorous, eating a variety of organisms including fish, amphibians (adults and larvae), arthropods, spiders (Araneae), snails (Campeloma), mollusks, isopods (Isopoda), millipedes (Diplopoda), and worms (Annelida) (Oldfield and Moriarty 1994, Ernst and Lovich 2009). Although A. mutica is a dietary generalist, it can be classified as an insectivore.

Arthropods typically consumed by smooth softshell turtles are aquatic and larval forms of Coleoptera, Diptera, Calliphoridae, Chironomidae, Cyclorrhapha, Empidae, Muscidae, Ephemeroptera, Tipulidae (Tipulo bicornis), Hemiptera, Hymenoptera, Homoptera, Isoptera, Lepidoptera, Ichneumonidae, Odonata, Neuroptera, Orthoptera, Plecoptera, and Trichoptera (Oldfield and Moriarty 1994, Ernst and Lovich 2009).

Fish species consumed by smooth softshell turtles include Castostomus commersoni, Cyprinella whipplei, Cyprinella spiloptera, Lepomis macrochirus, Morone chrysops, Hypentilium nigricans, Perca flavescens, and Salvelinus fontinalis (Ernst and Lovich 2009).

Although carnivorous, smooth softshell turtles occasionally eat vegetation such as algae, potatoes, seeds, stems, mulberry (Morus), fruits, and hard nuts (Ernst and Lovich 2009).

Smooth softshell turtles hunt on both land and in water (Oldfield and Moriarty 1994, Ernst and Lovich 2009). They are ambush predators; while concealed in substrate, they use their long neck to grab passing prey (Oldfield and Moriarty 1994, Ernst and Lovich 2009). They have also been observed pharyngeal gulping, in which they suck in nearby small prey organisms (Ernst and Lovich 2009). They also use their nose to seek food in sediment and vegetation (Oldfield and Moriarty 1994, Ernst and Lovich 2009).

Females generally utilize deeper water to obtain food, while males tend to forage in shallow water near the shore (Plummer and Farrar 1981). Although foraging area differs between sexes, food size does not vary with size or sex (Ernst and Lovich 2009).

Animal Foods: birds; mammals; amphibians; fish; carrion ; insects; terrestrial non-insect arthropods; mollusks; terrestrial worms; aquatic crustaceans

Plant Foods: leaves; roots and tubers; wood, bark, or stems; seeds, grains, and nuts; fruit; algae

Primary Diet: carnivore (Insectivore )

  • Plummer, M., D. Farrar. 1981. Sexual dietary differences in a population of Trionyx muticus. Journal of Herpetology, 15: 175-179.
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Associations

Ecosystem Roles

Smooth softshell turtles are aquatic predators and fall prey to a variety of organisms (Ernst and Lovich 2009). Eggs of this speices are parasitized by fly larvae (Sarcophagidae).

Commensal/Parasitic Species:

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Predation

Smooth softshell turtles are wary and abandon their basking place if danger is perceived (Oldfield and Moriarty 1994, Ernst and Lovich 2009). They are highly agile, both in water and on land, which permits quick escape from predators. They also use their strong diving ability to flee predators and conceal themselves in mud (Oldfield and Moriarty, Ernst and Lovich 2009). When caught by predators, a smooth softshell turtle pulls itself into its shell (Ernst and Lovich 2009).

Due to their high agility on land and water and these avoidance strategies, adults have few natural predators (Ernst and Lovich 2009). Humans and alligators are the main predator of adults (Ernst and Lovich 2009).

Predators of hatchlings include fish, other turtles (common snapping turtles, alligator snapping turtles, possibly adult Apalone), water snakes, shoreline birds, bald eagles, and other mammals (Oldfield and Moriarty 1994, Ernst and Lovich 2009).

Nest predation is usually from raccoons, skunks (Memphitis and Spilogale), crows, fire ants (Solenopsis invicta), fly larvae (Sarcophagidae), dogs, red foxes, moles (eastern moles, and other small mammals (Fitch and Plummer 1975, Oldfield and Moriarty 1994, Doody 1996, Watermolen 2004, Ernst and Lovich 2009).

Known Predators:

  • Fitch, H., M. Plummer. 1975. A preliminary ecological study of the soft-shelled turtle Trionyx muticus in the Kansas River. Israel Journal of Zoology, 24: 28-32.
  • Watermolen, D. 2004. Softshell turtles (g. Apalone) as bald eagle prey. Bulletin of Chicago Herpetological Society, 39: 69-70.
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General Ecology

Along the Kansas River in Kansas, Plummer (1977) estimated population density to be 1,900 individuals per 1.5 km of river (based on study of a major sandbar of that length); however, this estimate was influenced by temporary emigration and immigration from areas upstream and downstream; over the entire 14-km study area, Plummer made approximately 3,700 captures of 2,700 turtles; at least two-thirds of the population consisted of adults. Nest survivorship in Kansas was 0.43 (Fitch and Plummer 1975).

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Life History and Behavior

Behavior

Communication and Perception

Smooth softshell turtles primarily interact through visual and tactile cues. When seeking out mates, males physically investigate females. Although little information was found regarding perception and communication by this species, a close relative, Apalone spinifera, perceives its environment using chemical, visual, and tactile cues, vibrations (Bartholomew 2002) and communicates using tactile cues.

Communication Channels: tactile

Perception Channels: visual ; tactile ; vibrations ; chemical

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Cyclicity

Comments: Active from April to October in ne. Kansas (Collins 1982).

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Life Cycle

Development

Embyonic development of smooth softshell turtles is categorized into three stages: division of cells and tissue development, organogenesis, and the growth of the embryo before the hatching stage (Nagle et al. 2003). The timing of these three stages is related to three equal corresponding periods during incubation (Ewert 1985). Sex determination is not temperature dependent, and relatively equal proportions of hatchlings are male and female (Ernst and Lovich 2009).

With time, the round shape of a hatchling smooth softshell turtle's carapace changes to an oval shape through allometric growth. There is no change, however, in plastron shape as the hatchling grows, making for little change in the straight carapace length/plastron length (SCL/PL) ratio. Once the plastron has reached a minimum length of 60 mm, individuals can be sexed using physical characteristics described above. Unlike many other species of turtles, smooth softshell turtles do not form growth annuli on their shells, making them difficult to age in the field (Ernst and Lovich 2009).

Growth of smooth softsell turtles typically occurs from May to September, and growth rates are usually highest from June to August (Plummer 1977). Males grow on average 1.95 mm/month when between lengths of 61 and 65 mm (Ernst and Lovich 2009). At a plastron length (PL) of 66 to 75 mm, males grow at a rate of 2.1 to 2.5 mm/month. This rate decreases to 0.09 mm/month when males reach a PL of 111 to 115 mm (Ernst and Lovich 2009). Females exhibit a faster growth rate than males. In females with a PL of 61 to 70 mm, growth rate is 2.8 mm/month. This decreases to 0.7 mm/month at a PL of 151 to 160 mm. Most species of turtles experience indeterminate growth (Browne and Hecnar 2007), although this has not verified for this species.

Development - Life Cycle: indeterminate growth

  • Browne, C., S. Hecnar. 2007. Species loss and shifting population structure of freshwater turtles despite habitat protection. Biological Conservation, 138: 421-429.
  • Ewert, M. 1985. Embryology of turtles. Pp. 75-268 in C Gans, F Billett, P Maderson, eds. Biology of the Reptilia, Vol. 14. New York, New York: John Wiley and Sons.
  • Nagle, R., M. Plummer, J. Congdon, R. Fischer. 2003. Parental investment, embryo growth, and hatchling lipid reserves in softshell turtles (Apalone mutica) from Arkansas. Herpetologica, 59: 145-154.
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Life Expectancy

Lifespan/Longevity

Unlike many other species of turtles, smooth softshell turtles do not form growth annuli on their shells, which makes them very difficult to age in the field (Ernst and Lovich 2009). The lifespan of this species is unrecorded (Ernst and Lovich 2009). Individuals in captivity have lived over 11 years, and they are believed to be capable of living 20 years (Ernst and Lovich 2009). Florida softshell turtles, Apalone ferox, and spiny softshell turtles, Apalone spinifera, can live up to 25 years in captivity (Snider and Bowler 1992).

Average lifespan

Status: captivity:
11 years.

  • Snider, A., J. Bowler. 1992. Longevity of Reptiles and Amphibians in North American Collections. Pp. 1-44 in J Collins, ed. Herpetological Circular, Vol. 21. Utah: Society for the Study of Amphibians and Reptiles.
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Lifespan, longevity, and ageing

Observations: In captivity animals may live up to 11 years. Still, longevity in the wild should be higher and some animals are estimated to live over 20 years (http://www.pwrc.usgs.gov/neparc/).
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Reproduction

Lays 1-3 clutches of 4-33 eggs, May to July. Eggs hatch in 2 to 2.5 months. Females sexually mature in about 6-9 years, males in 4 years (Collins 1982).

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Breeding activity of smooth softshell turtles occurs from April to June and possibly into September (Ernst and Lovich 2009). Males seek out females by approaching other adults (Oldfield and Moriarty 1994; Ernst and Lovich 2009). If the approached individual is male, the response to the investigation is usually passive but can be aggressive on occasion (Ernst and Lovich 2009). Non-receptive females are often aggressive; during the breeding season many males are observed with wounds inflicted by females. Receptive females, on the other hand, are passive to the advances of a male (Ernst and Lovich 2009). Many males may be present near a receptive female, and all may attempt to mate with her. When there is only one male present, the female may chase the male (Ernst and Lovich 2009).

Copulation almost always occurs in the water, and a sexually receptive female is mounted from behind (Ernst and Barbour 1972). Deep water is usually needed to successfully mount a female and a male must swim in place for upwards of 20 min to keep his position (Ernst and Lovich 2009). During this time, the male needs to keep its vents aligned (Ernst and Lovich 2009).

Mating System: polygynous

Smooth softshell turtles nest between late May and July (Ernst and Lovich 2009). In more northern locations such as Minnesota and Wisconsin, nesting typically takes place from June to early July (Vogt 1981). Any disturbance can cause early abandonment of the nest by wary females (Oldfield and Moriarty 1994).

Females dig a nest cavity 15 to 30 cm deep with their hind feet. Nests are typically located on a sand bar with little vegetation, although some nests have been found in dense vegetation (Ernst and Lovich 2009). Nests are generally located within 18 m of the water and only rarely are more than 30 m away from water (Oldfield and Moriarty 1994; Ernst and Lovich 2009). Nests are usually 0.5 to 6.1 m above the water. Nest density can be quite high, and in some cases there are connecting chambers between nests (Ernst and Lovich 2009).

Oviposition usually occurs in the early morning (Ernst and Lovich 2009). Eggs are laid in two layers in the nesting chamber. Females cover their eggs with sand using their hind feet. A female then usually burrows a tunnel and places herself on the opposite end of the nest. This tunnel can be up to 4 m in length (Plummer 1976).

Female smooth softshell turtles lay only one clutch per year ("Smooth softshell (Apalone mutica)" 2009). Average clutch size is 15 to 25 eggs. The minimum observed clutch size is 1 egg while the maximum clutch size observed is 33 eggs (Ernst and Barbour 1972). Clutches laid later in the season are usually smaller in size than early season clutches (Ernst and Lovich 2009). The size of a clutch is proportional to the straight carapace length (SCL) of the female. Eggs are a spheroidal shape and resemble ping-pong balls (Oldfield and Moriarty 1994). In a typical clutch, 75% of eggs are likely to survive. Predation and flooding can have large effects on egg survival (Plummer 1976; Oldfield and Moriarty 1994; Doody 1996).

Eggs generally hatch in 8 to 12 weeks. Hatching frequency is highest in August to September (Ernst and Lovich 2009). Hatchlings use their front claws to break through the egg, relying on their claws more than their caruncle (egg tooth), which is less used in comparison to other species (Oldfield and Moriarty 1994). Hatchlings generally emerge from the nest around sunset (Ernst and Lovich 2009).

Hatchlings are completely independent upon the moment of hatching. Recently hatched smooth softshell turtles average 4 cm in straight carapace length (SCL; Oldfield and Moriarty 1994) and have a body mass of 3.0 to 7.5 g (mean 5.4 g). Caruncles drop off in a week, and the umbilical scar is usually 2 mm in diameter (Ernst and Lovich 2009).

Male smooth softshell turtles become sexually mature during their fourth year with mean plastron length (PL) ranging from 80 to 85 mm. Females become sexually mature during their ninth year with mean PL ranging from 140 to 150 mm (Ernst and Lovich 2009). Mature individuals attempt to mate immediately upon emergence from hibernation (Plummer and Shirer 1975; Plummer 1977; Oldfield and Moriarty 1994). The volume of mature male testes varies with season, with testes reaching a maximum diameter immediately before hibernation. In April and May, the vas deferens of males become swollen, 2 mm in diameter (Ernst and Lovich 2009). The vas deferens is no longer swollen by June but become swollen with sperm once more by October. Vitellogenesis in females begins in July in Kansas (Ernst and Lovich 2009).

Breeding interval: Female smooth softshell turtles have one clutch per year.

Breeding season: In Minnesota, breeding occurs in May and June, and nesting occurs in June and July.

Range number of offspring: 1 to 33.

Average number of offspring: 15 to 25.

Range gestation period: 8 to 12 weeks.

Range birth mass: 3 to 7.5 g.

Average birth mass: 5.4 g.

Range age at sexual or reproductive maturity (female): 7 (low) years.

Average age at sexual or reproductive maturity (female): 9 years.

Average age at sexual or reproductive maturity (male): 4 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous

Smooth softshell turtles provide pre-natal care for their offspring. Females produce high levels of non-polar lipids that provide energy for their growing embryos (Nagle et al. 2003). They produce energy at a level much higher than what is necessary to keep the embryos alive, which is known as parental investment in embryogenesis (PIE; Nagle et al. 2003).

Hatchlings are born with high concentrations of lipids, which act as a food source until they are mature enough to begin feeding (Nagle et al. 2003, Ernst and Lovich 2009). This allocation of energy into high storage reserves for hatchlings represents parental investment in care (PIC; Nagle et al. 2003). This provisioning of lipids enables hatchlings to survive in areas that have low resource availability.

Parental Investment: pre-hatching/birth (Provisioning: Female)

  • 2009. "Smooth softshell (Apalone mutica)" (On-line). Wisconsin Department of Natural Resources. Accessed April 15, 2011 at http://dnr.wi.gov/org/land/er/biodiversity/index.asp?mode=info&Grp=49&SpecCode=ARAAG01020.
  • Doody, J. 1996. Summers with softshells. Bulletin of Chicago Herpetological Society, 31: 132-133.
  • Ernst, C., R. Barbour. 1972. Turtles of the United States. Lexington, Kentucky: University Press Kentucky.
  • Ernst, C., J. Lovich. 2009. Turtles of the United States and Canada. Baltimore, Maryland: The John Hopkins University Press.
  • Nagle, R., M. Plummer, J. Congdon, R. Fischer. 2003. Parental investment, embryo growth, and hatchling lipid reserves in softshell turtles (Apalone mutica) from Arkansas. Herpetologica, 59: 145-154.
  • Oldfield, B., J. Moriarty. 1994. Amphibians & Reptiles Native to Minnesota. Minneapolis, Minnesota: University of Minnesota Press.
  • Plummer, M. 1977. Activity, habitat, and population structure in the turtle, Trionyx muticus. Copeia, 3: 431-440.
  • Plummer, M. 1976. Some aspects of nesting success in the turtle, Trionyx muticus. Herpetologica, 32: 353-359.
  • Plummer, M., H. Shirer. 1975. Movement patterns in a river population of the softshell turtle Trionyx muticus. University of Kansas Museum of Natural History Occasional Papers, 43: 1-26.
  • Vogt, R. 1981. Natural History of Amphibians and Reptiles of Wisconsin. Wisconsin: Milwaukee Public Museum.
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N5 - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2011

Assessor/s
van Dijk, P.P.

Reviewer/s

Contributor/s

Justification
Apalone mutica is a reasonably widespread, fairly cryptic, and locally common species with high reproductive potential by turtle standards. Extensive areas of suitable habitat exist and are likely to remain for the foreseeable future. Harvest rates appear not significant enough to have led to documented localised declines. Nevertheless, this assessment is more an issue of lack of data documenting a decline than available data indicating stable populations; population monitoring is highly desirable as the species can be argued to warrant Near Threatened. It is however currently listed as Least Concern.
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Although smooth softshell turtles are listed as a speices of least concern by the IUCN, little data is available to make a confident assessment. Currently, this species is widespread and locally common, suitable habitat is present, and harvest rates do not contribute to decline.

However, their ability to absorb oxygen from the water has made smooth softshell turtles susceptible to water pollution (Pappas et al. 2001, Trauth et al. 2004, Ernst and Lovich 2009). Other negative impacts include habitat degradation, harvesting for food, changes in hydrological regimes (construction of dams and locks), and an increase in human disturbances at nesting sites (Moll and Moll 2000, Ernst and Lovich 2009). Human disturbance includes boating near nest sites, with waves resulting from boat use causing erosion and egg exposure (Minnesota Department of Natural Resources 2011). This species is also caught as bycatch (capture of non-target species) in the commercial fishing industry (Pappas et al. 2001).

Efforts to conserve smooth softshell turtle should include the protection of waterways and surrounding terrestrial land that are known to support large populations of this species (Ernst et al. 1994). Upstream sites should also be protected (Moll and Moll 2000). Protected areas ideally should include basking and nesting habitats with high densities of prey, hibernation areas, and be of ample size to support home ranges (Minnesota Department of Natural Resources 2011).

Smooth softshell turtles are listed as a species of special concern in the state of Minnesota. Their slow maturation rate increases time necessary to restore populations (Minnesota Department of Natural Resources 2011).

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: no special status

  • Moll, E., D. Moll. 2000. Conservation of river turtles. Pp. 126-155 in M Klemens, ed. Turtle Conservation. Washington D.C.: Smithsonian Institution Press.
  • Pappas, M., J. Congdon, A. Pappas. 2001. Weaver Bottoms 2001 turtle survey: management and conservation concerns. Nongame Wildlife Survey, Minnesota Department of Natural Resources and U.S. Fish and Wildlife Service.
  • van Dijk, P. 2010. "Apalone mutica" (On-line). In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.1. Accessed July 05, 2011 at http://www.iucnredlist.org/apps/redlist/details/165596/0.
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Population

Population
Apalone mutica can reach substantial densities, up to 1.2 individuals per linear meter of river, and a basking aggregation of 88 animals was reported (Plummer 1977, Trauth et al. 2004). However, there have been anecdotal observations of declining populations, at least locally, as well as consistently failing recruitment as a result of water level regulation in large rivers flooding nesting banks (Janzen pers. comm. 2010).

Population Trend
Unknown
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Threats

Major Threats
The impact of commercial exploitation appears undocumented and unquantified, though bycatch in commercial fisheries and recreational fishing has been suspected to be a factor in the observed decline in at least some populations (Janzen pers. comm. 2010).

Water pollution has been implicated in population reductions (Trauth et al. 2004). Increasingly frequent flooding events, resulting from a combination of anthropogenic activities upstream (increased hard surface area, increased stormwater runoff volumes and speed) and changing, more pulsed, precipitation patterns, consistently impact nesting areas and may preclude successful reproduction (e.g., Cedar River, Iowa) (Janzen pers. comm. 2010).
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Management

Conservation Actions

Conservation Actions
Apalone mutica is subject to a variety of State legislation and regulations, and likely occurs in several protected areas.
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Although smooth softshell turtles may prey upon game fish, their impact on fish populations is believed to be insignificant (Ernst and Barbour 1972). There are no known adverse effects of Apalone mutica on humans, although they may bite when handled.

Negative Impacts: injures humans (bites or stings)

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Economic Importance for Humans: Positive

In some regions, adults and eggs are gathered for food (Ernst and Lovich 2009). Additionally, this species is occasionally a part of the pet trade.

Positive Impacts: pet trade ; food

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Wikipedia

Smooth softshell turtle

The smooth softshell turtle (Apalone mutica) is a softshell turtle of the family Trionychidae. It is endemic to North America.

Contents

Geographic range

It lives mainly in the Mississippi River drainage, including the Ohio River and the lower Allegheny River.

Description

The smooth softshell turtle is usually brown or olive-colored, often with darker dots or dashes. It is the only softshell without ridges in the nostrils. Females are 18-35.6 cm (7-14 inches); males, 12.5-17.8 cm (5-7 inches).

Reproduction

From May to July, the females lay bunches of three to 28 eggs about 100 m from water in sandy areas.[3]

Sympatric species

Apalone mutica is sympatric with the spiny softsl turtle (Apalone spinifera) over much of its range.[4]

References

  1. ^ ITIS.gov
  2. ^ Fritz Uwe; Peter Havaš (2007). "Checklist of Chelonians of the World". Vertebrate Zoology 57 (2): 306. ISSN 18640-5755. Archived from the original on 2010-12-17. http://www.webcitation.org/5v20ztMND. Retrieved 29 May 2012.
  3. ^ DNr.wi.gov
  4. ^ JSTOR.org
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Names and Taxonomy

Taxonomy

Comments: Removed from genus Trionyx and placed in genus Apalone by Meylan (1987). North American softshell turtles were retained in Trionyx by Webb (1990) and Ernst et al. (1994).

Molecular data indicate a genetic dichotomy between populations north and west of Louisiana and populations from the Gulf Coast in southeastern North America (Weisrock and Janzen 2000).

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