Smooth softshell turtles are aquatic predators and fall prey to a variety of organisms. Eggs of this speices are parasitized by fly larvae (Sarcophagidae).
Commensal/Parasitic Species:
Due to their high agility on land and water and these avoidance strategies, adults have few natural predators. Humans and alligators are the main predator of adults. 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. 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.
Smooth softshell turtles are wary and abandon their basking place if danger is perceived. 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. When caught by predators, a smooth softshell turtle pulls itself into its shell.
Known Predators:
Smooth softshell turtles are medium to large freshwater turtles. Females have a back shell that is 16.5 to 35.6 cm long. Females are larger than males, who have a shell that is 11.5 to 26.6 cm long. Like other softshell turtles, smooth softshell turtles have a carapace that is covered by skin instead of the hard scutes commonly observed in other turtle species. The carapace is ovoid and lacks spines on the front edge. The coloring of the carapace ranges from olive to orange. Females typically have a tan or brown carapace, while males have a brown or gray carapace. 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. 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. Juvenile smooth softshell turtles do not differ in coloration from adults, but juveniles of subspecies are used to tell them apart in the field. Hatchlings have a brown or olive carapace with many markings on the carapace.
Smooth softshell turtles have a tubular snout with round nostrils that are usually positioned inferior, and they lack a septal ridge. Male smooth softshell turtles have thicker tails than females, a trait commonly observed in turtle species. 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. As with other species of turtles, female smooth softshells have longer hind claws than males, which have longer foreclaws than females.
Smooth softshell turtles are the most aquatic of all North American softshells. 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. Water exchange in freshwater is typically 6.3 mL/100g wet BM/hour. The lining of the cloaca and pharynx enables uptake of oxygen from the water. Furthermore, the surface of their shell and skin is cutaneous, increasing the permeability of gases and water. For instance, smooth softshell turtles lose about 64% of respiration-produced carbon dioxide through their skin. Their long neck and snout contribute to the ability to remain submerged for extensive periods of time.
Smooth softshell turtles are mostly easily confused with spiny softshell turtles (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.
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
Other Physical Features: ectothermic ; bilateral symmetry
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. The lifespan of this species is unrecorded. Individuals in captivity have lived over 11 years, and they are believed to be capable of living 20 years. Florida softshell turtles (Apalone ferox) and spiny softshell turtles (Apalone spinifera) can live up to 25 years in captivity.
Average lifespan
Status: captivity: 11 years.
Smooth softshell turtles are typically found along major riverine systems such as the Ohio, Missouri, and Mississippi rivers. They prefer large rivers and streams with medium to fast currents . 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. Despite their preference for riverine systems, smooth softshell turtles have also been found in lakes, bogs, ponds, and drainage ditches. 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. 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.
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
Smooth softshell turtles are native to temperate areas of North America, ranging throughout the central and south-central United States. Their range extends from Pennsylvania to New Mexico and south to the Florida panhandle. This species is thought to have been extirpated from Pennsylvania. Smooth softshell turtles are believed to have occurred in North America since the Cretaceous Period, although this is not yet supported by fossil evidence. 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.
Biogeographic Regions: nearctic (Native ); palearctic (Introduced )
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). 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. 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. Although primarily carnivorous, smooth softshell turtles occasionally eat vegetation such as algae, potatoes, seeds, stems, mulberry (Morus), fruits, and hard nuts.
Smooth softshell turtles hunt on both land and in water. They are ambush predators; while concealed in substrate, they use their long neck to grab passing prey. They have also been observed pharyngeal gulping, in which they suck in nearby small prey organisms. They also use their nose to seek food in sediment and vegetation. Females generally utilize deeper water to obtain food, while males tend to forage in shallow water near the shore. Although foraging area differs between sexes, food size does not vary with size or sex.
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 )
In some regions, adults and eggs are gathered for food. Additionally, this species is occasionally a part of the pet trade.
Positive Impacts: pet trade ; food
Although smooth softshell turtles may prey upon game fish, their impact on fish populations is believed to be insignificant. There are no known adverse effects of smooth softshell turtles on humans, although they may bite when handled.
Negative Impacts: injures humans (bites or stings)
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. The timing of these three stages is related to three equal corresponding periods during incubation. Sex determination is not temperature dependent, and relatively equal proportions of hatchlings are male and female.
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.
Growth of smooth softsell turtles typically occurs from May to September, and growth rates are usually highest from June to August. Males grow on average 1.95 mm/month when between lengths of 61 and 65 mm. 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. 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, although this has not verified for this species.
Development - Life Cycle: indeterminate growth
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. 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.
Their ability to absorb oxygen from the water has made smooth softshell turtles susceptible to water pollution. 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. Human disturbance includes boating near nest sites, with waves resulting from boat use causing erosion and egg exposure. This species is also caught as bycatch (capture of non-target species) in the commercial fishing industry.
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. Upstream sites should also be protected. 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.
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
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, spiny softshell turtles (Apalone spinifera), perceives its environment using chemical, visual, and tactile cues, vibrations and communicates using tactile cues.
Communication Channels: tactile
Perception Channels: visual ; tactile ; vibrations ; chemical
Apalone mutica was previously known as Trionyx muticus.
Breeding activity of smooth softshell turtles occurs from April to June and possibly into September. Males seek out females by approaching other adults. If the approached individual is male, the response to the investigation is usually passive but can be aggressive on occasion. 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. 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.
Copulation almost always occurs in the water, and a sexually receptive female is mounted from behind. 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. During this time, the male needs to keep its vents aligned.
Mating System: polygynous
Smooth softshell turtles nest between late May and July. In more northern locations such as Minnesota and Wisconsin, nesting typically takes place from June to early July. Any disturbance can cause early abandonment of the nest by wary females. 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. Nests are generally located within 18 m of the water and only rarely are more than 30 m away from water. 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. Oviposition usually occurs in the early morning. 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.
Female smooth softshell turtles lay only one clutch per year. 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. Clutches laid later in the season are usually smaller in size than early season clutches. 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. In a typical clutch, 75% of eggs are likely to survive. Predation and flooding can have large effects on egg survival.
Eggs generally hatch in 8 to 12 weeks. Hatching frequency is highest in August to September. 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. Hatchlings generally emerge from the nest around sunset. At the moment of hatching, hatchlings are completely independent. Recently hatched smooth softshell turtles average 4 cm in straight carapace length 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.
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. Mature individuals attempt to mate immediately upon emergence from hibernation. 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. 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.
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 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 prenatal care for their offspring. Females produce high levels of non-polar lipids that provide energy for their growing embryos. 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. At birth, hatchlings have high concentrations of lipids. These act as a food source until they are mature enough to begin feeding. This allocation of energy into high storage reserves for hatchlings represents parental investment in care. This provisioning of lipids enables hatchlings to survive in areas that have low resource availability.
Parental Investment: pre-hatching/birth (Provisioning: Female)
The smooth softshell turtle (Apalone mutica) is a species of softshell turtle of the family Trionychidae. The species is endemic to North America.
A. mutica is native to North America. It is distributed throughout the central and southcentral United States as its geographic range extends from western Pennsylvania to New Mexico and south to the Florida panhandle. Smooth softshells turtles inhabit the Mississippi River drainage from Louisiana up to North Dakota and Pennsylvania, as well as the Colorado, Brazos, Sabine, and Pearl, Alabama and Escambia river systems.[1] Two subspecies of A. mutica have been identified. The midland smooth softshell, Apalone mutica mutica, is found throughout the central United States. The other subspecies, Apalone mutica calvata, is found ranging from Louisiana to the panhandle of Florida.[4]
Both subspecies of A. mutica are typically found in medium to large unpolluted rivers with moderate to fast currents, but are also found in standing water bodies like lakes, ponds and marshes. They prefer water with sand or mud bottoms, without rocky areas or dense vegetation. Sandbanks must also be present.[1]
The smooth softshell turtle has an anapsid skull. This kind of skull is present among the earliest reptiles and is retained by turtles today. The anapsid skull lacks openings behind the orbits.[5] The smooth softshell turtle has a smooth, flexible and leather like carapace that is covered by skin instead of the hard scutes commonly observed in other turtle species.[6] The plastron is light (white or gray) with no markings, and the underlying bones are visible.[7] Smooth softshell turtles have a tubular snout with round nostrils.[8]
There is sexual dimorphism between females and males of A. mutica as females are larger than males. A female has a carapace length of 16.5–35.6 cm (6.5–14.0 in) compared to a carapace length of 11.4–17.8 cm (4.5–7.0 in) for males.[6] Additionally, the female smooth softshell turtle is usually brown or olive-colored with irregular dark brown blotches, while the carapace of males and juveniles is a brown or grayish color with dark dots or dashes.[1] Sexual dimorphism is also apparent in the size of the tails and claws. Males have thicker tails than females, but females have longer hind claws than males.[8]
The smooth softshell turtle may be easily confused with the spiny softshell turtle (Apalone spinifera), as the differences between the two species are subtle. The spiny softshell turtle has a rough carapace with spines along the front edge while, as the name implies, the smooth softshell turtle lacks such spines.[9] Additionally, the white chin and throat of the smooth softshell are unmarked, compared to the splotchy chin and throat of the spiny softshell.[9] A. mutica is the only species of North American softshell with round nostrils; all other species have ridges on the nasal septum which make the nostrils C-shaped.[10]
The smooth softshell turtle is mostly carnivorous, eating aquatic insects, crayfish, fish and amphibians.[11] Although primarily carnivorous, it sometimes resorts to eating vegetation such as algae, vegetables, fruits, and nuts.[7]
Breeding of the smooth softshell turtle occurs from April to June. The mating system utilized by these turtles is polygyny, meaning that males will mate with more than one female. Males actively seek out females by approaching other adults. If the other party is male or a non-receptive female, aggression may be displayed. However, if the other party is a receptive female, she remains passive to the advancements of the males. Copulation usually occurs in deep pools as the male mounts the female.[8] The nesting period is usually from May to July as females only lay eggs once a year.[7] During this period, adult females of A. mutica lay clutches of 3 to 28 eggs not more than 100 m (330 ft) from water in sandy areas.[12] Eggs generally hatch 8 to 12 weeks later with the highest frequency of hatching being between August and September. Hatchlings average a weight of 5.4 g (0.19 oz) and have a carapace length of 4 cm (1.6 in). Male smooth softshell turtles become sexually mature during their fourth year and females become sexually mature during their ninth year.[4]
Female turtles offer prenatal care for their offspring. They produce high levels of non-polar lipids that provide energy for their growing embryos.[13] This energy is more than enough to keep the embryos alive. The high concentration of lipids also offer an advantage at birth as it acts as a food source until they hatchlings become mature enough to commence feeding. This type of care is also known as parental investment in embryogenesis. However, after hatching no physical parental care is given.[13]
The smooth softshell turtle is the most aquatic of the softshell turtles as it is often referred to as a "swimmer".[14] It is able to stay underwater for extended periods of time due to its long neck and tubular snout. It often buries itself in the sand substrate at the bottom of a river or pool just deep enough so that its snout barely reaches the surface.[7] Additionally, the skin covering the shell allows for a high rate of gas exchange. This enables the turtle to stay submerged for a long period of time. In this position, it often waits for prey to pass and utilizes its long neck to capture the prey.[6]
The smooth softshell turtle hibernates in the months of October to March. It hibernates by burying itself in substrate underwater. After emerging from hibernation, it is often found on land basking in the sun. Given that its shell is a soft shell, it is unable to stay in the sun for extended periods of time.[14] When basking, it is wary of its surroundings, and if any threat presents itself, it is quick to abandon its basking site to seek safety. Its agility on land and water makes it a difficult prey item for predators such as raccoons, humans, alligators and snapping turtles.[8] It seeks shelter from these threats by diving and concealing itself in mud.[8]
Currently, the smooth softshell turtle is considered a species of least conservation concern. However, the species is still facing some wide-ranged threats.[1] These threats include habitat degradation, harvesting for food, and an increase in human disturbances at nesting sites. Additionally, due to its skin's high rate of gas exchange, it is very susceptible to polluted waters.[6] As a result of all of these factors, the smooth softshell turtle has been listed as a species of special concern in Minnesota and Wisconsin.[6][15]
Two subspecies are recognized, including the nominotypical subspecies.[16]
Nota bene: A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Apalone.
Apalone mutica is sympatric with the spiny softshell turtle (Apalone spinifera) over much of its range.[17]
The smooth softshell turtle (Apalone mutica) is a species of softshell turtle of the family Trionychidae. The species is endemic to North America.
