Apalone mutica

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. (Ernst and Lovich, 2009; Hulse, et al., 2001; Oldfield and Moriarty, 1994; Quammen, 1992)

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). (Ernst, et al., 1994)

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. (Barko and Briggler, 2006; Bodie, et al., 2000; Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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. (Plummer, 1977)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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. (Ernst and Lovich, 2009; Minnesota Department of Natural Resources, 2011; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (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. (Ernst and Lovich, 2009)

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). (Ernst and Lovich, 2009; Jackson, et al., 1976; Oldfield and Moriarty, 1994; Stone and Iverson, 1999)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Ewert, 1985; Nagle, et al., 2003)

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). (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. (Browne and Hecnar, 2007; Ernst and Lovich, 2009; Plummer, 1977)

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). (Ernst and Barbour, 1972; Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994; Plummer, 1976; Vogt, 1981)

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). ("Smooth softshell (Apalone mutica)", 2009; Doody, 1996; Ernst and Barbour, 1972; Ernst and Lovich, 2009; Oldfield and Moriarty, 1994; Plummer, 1976)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Plummer and Shirer, 1975; Plummer, 1977)

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. (Ernst and Lovich, 2009; Nagle, et al., 2003)

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). (Ernst and Lovich, 2009; Snider and Bowler, 1992)

Smooth softshell turtles are the most aquatic of all North American softshells (Ernst and Lovich 2009). Behavioral and morphological adaptations permit their aquatic nature. Smooth softshell turtles are able to remain submerged for extensive periods of time, which is made possible in part by their long neck and snout (Oldfield and Moriarty 1994). They often bury themselves in the substrate of a body of water deep enough so their snout just barely reaches the surface (Ernst and Lovich 2009). To achieve this position, a smooth softshell turtle pushes itself head-first into the sediment; it pulls itself with its frontlimbs while pushing with its hindlimbs. When its body is positioned tilting downward toward the front, it stirs up the sediment. The falling material covers the turtle so only its head is visible (Ernst and Lovich 2009). (Ernst and Lovich, 2009; Jackson, et al., 1976; Oldfield and Moriarty, 1994)

Smooth solfshell turtles hibernate by burying themselves in substrate underwater (Ernst and Lovich 2009). They emerge from winter hibernation in March or early April in Kansas and in May in northern areas such as Minnesota and Wisconsin (Vogt 1981). Activity of smooth softshell turtles is typically observed from May through September (Plummer 1977, Vogt 1981). In more southern regions such as New Mexico, members of this species are usually active from April to October (Degenhardt et al. 1996).

After emerging from hibernation, smooth softshell turtles are often observed basking on sand bars or in shallow water between 0700 and 1700 hours (Lindeman 2000). Sandy and muddy bars within a few meters of the water's edge are preferred basking sites, although logs and rocks near the water may also be used. When basking, smooth softshell turtles extend their neck and tuck their limbs into their shell (Ernst and Lovich 2009). (Degenhardt, et al., 1996; Ernst and Lovich, 2009; Lindeman, 2000; Plummer, 1977; Vogt, 1981)

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 as well as feeding on fast-moving prey (Oldfield and Moriarty 1994, Ernst and Lovich 2009). Members of this species are generally solitary. (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

Due to the high frequency of time spent in water, most recorded movements of smooth softshell turtles are aquatic-based. During the breeding season, females move around land bars during their search for suitable nesting habitat (Ernst and Lovich 2009).

In a study conducted by Plummer and Shirer (1975), radio-equipped males in Kansas had a mean linear home range of 474 m. The mean linear home range of subadult females was 750 m and of adult females was 1,228 m. Adult females had the greatest activity within their home range (Plummer and Shirer 1975) (Ernst and Lovich, 2009; Plummer and Shirer, 1975)

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. (Bartholomew, 2002; Ernst and Lovich, 2009)

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. (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994)

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). (Ernst and Lovich, 2009; Oldfield and Moriarty, 1994; Plummer and Farrar, 1981)

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). (Doody, 1996; Ernst and Lovich, 2009; Fitch and Plummer, 1975; Oldfield and Moriarty, 1994; Watermolen, 2004)

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). (Ernst and Lovich, 2009)

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. (Ernst and Lovich, 2009)

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. (Ernst and Barbour, 1972)

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). (Ernst and Lovich, 2009; Minnesota Department of Natural Resources, 2011; Moll and Moll, 2000; Pappas, et al., 2001; van Dijk, 2010)

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). (Ernst, et al., 1994; Minnesota Department of Natural Resources, 2011; Moll and Moll, 2000)

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). (Minnesota Department of Natural Resources, 2011)

Apalone mutica was previously known as Trionyx muticus (Ernst and Lovich 2009). (Ernst and Lovich, 2009)