Spiny Softshell - Apalone spinifera
The shell of the Spiny Softshell is flattened (pancake-like), with flexible edges and covered with leathery skin; small conical tubercles or "spines" are present on the front edge of the carapace above the neck. The snout is tubular, with a ridge along the inner margin of each nostril, which allows this turtle to remain beneath the surface with just the snout exposed. In mature males, the carapace is like sandpaper, and marked with small dark spots or circles. The tail is thick and long, with the vent well beyond the rear edge of the carapace. In mature females, the carapace is not notably like sandpaper, is more generally mottled or marked with blotches, the tubercles at the front edge of the carapace are more prominent than in males, and the tail is relatively short. Juveniles have characteristics that are female-like, except the carapace coloration, which is male-like. In hatchlings, the carapace is olive to tan, with small dark circles, spots, or dashes, and a yellowish margin bordered by a black line. The eggs are hard and white, smooth, thick-shelled, and about 24 to 32 millimeters in diameter. Adult females can reach 52 centimeters in carapace length, but much less in adult males (which average about 10 centimeters shorter); hatchlings are about 3 to 4 centimeters in carapace length.
The Spiny Softshell differs from other Montana turtles by having a flattened and leathery shell that is soft and lacks horny plates, and a pointed snout with tubular nostrils. The Smooth Softshell (A. muticus), which occurs in the Missouri River in southern North Dakota, differs by lacking the ridge on the inner margin of each tubular nostril and the absence of tubercles or spines along the front edge of the carapace.
Western Hemisphere Range
Observations in Montana Natural Heritage Program Database
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(Observations spanning multiple months or years are excluded from time charts)
No specific information is available for Montana. In Vermont, Spiny Softshells migrated about 3 kilometers between riverine wintering sites and river mouth nesting sites near Lake Champlain; migratory movements were most extensive in spring and late summer (Graham and Graham 1997). Annual home range size in Arkansas was 784 to 2,310 meters of stream length for males and 683 to 2,145 meters for females (Hammerson 1999).
Habitat use by Spiny Softshells in Montana is probably similar to elsewhere in the range, but studies are lacking and there is little qualitative information available. They occupy larger rivers and tributaries. Both sexes have been observed basking together on partially submerged logs in backwater sites of slow-moving water, and on sandy or muddy riverbanks.
Generally, the Spiny Softshell is primarily a riverine species, occupying large rivers and river impoundments, but also occurs in lakes, ponds along rivers, pools along intermittent streams, bayous, irrigation canals, and oxbows. It usually is found in areas with open sandy or mud banks, a soft bottom, and submerged brush and other debris. Spiny Softshells bask on shores or on partially submerged logs. They burrow into the bottoms of permanent water bodies, either shallow or relatively deep (0.5 to 7.0 meters), where they spend winter. Eggs are laid in nests dug in open areas in sand, gravel, or soft soil near water (Baxter and Stone 1985, Ernst et al. 1994, Hammerson 1999, Stebbins 2003).
Ecological Systems Associated with this Species
- Details on Creation and Suggested Uses and Limitations
How Associations Were Made
We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.
In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.
However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if
point observations were associated with that system.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.
The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
Suggested Uses and Limitations
Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.
These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: mtnhp.org/requests
) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.
Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.
Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.
Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).
Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
- Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
- Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
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- Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
- Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
- Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
- Commonly Associated with these Ecological Systems
Wetland and Riparian Systems
- Occasionally Associated with these Ecological Systems
Recently Disturbed or Modified
Wetland and Riparian Systems
The food habits in Montana have not been studied.
Generally, Spiny Softshells forage in the water, often in shallows with vegetation. They are considered to be generalist carnivores, and usually feed on the bottom. Major foods are crayfish, aquatic insects (of at least seven orders), and fishes, but mollusks, worms, isopods, amphibians, carrion, and vegetation also are eaten (Ernst et al. 1994, Hammerson 1999). The diet in an Iowa study was about 25% insects, 36.5% fish as carrion, 5.8% small fish as live prey, and 55% crayfish, with plant material in 61% of the stomachs sampled; this breakdown of categories appears representative for other states (Ernst et al. 1994). Prey may be chased, ambushed, or flushed and pursued.
Animals are active from April to October (usually May to September) in Kentucky and Colorado (Ernst et al. 1994, Hammerson 1999). Water temperatures of 12 degrees C. appear to determine when animals enter or emerge from hibernation in Vermont (Graham and Graham 1997). Adults emerge earlier from hibernation, and remain active longer into the fall, than juveniles. The period of activity in Montana is poorly documented, with records from early June to late July (Hendricks and Reichel 1996, Hendricks 1999). Egg predators include Striped and Spotted Skunks, Raccoon, Red Foxes, and probably Coyotes; young Spiny Softshells are captured and eaten by predatory fish, wading birds, and Muskrats (Ernst et al. 1994, Hammerson 1999). Some individuals are caught by anglers using live or dead bait, and then killed. No information on predators is available from Montana, but some adults are incidentally captured and killed by anglers.
Males reach maturity at about 8-9 cm plastron (belly shell) length, females at 18-20 cm. Mating occurs in April or May, and nesting may begin in late May and extend into August, but usually occurs in June and July in Colorado. Eggs are laid in one or more clutches in flask-shaped ground nests excavated in course sand or fine gravel to depths of 10-25 cm deep; Colorado nests contained 15-39 eggs, some clutches elsewhere contained as few as 4 eggs. Eggs hatch in about 60-80 days; hatching occurs in August to September in Colorado. Some hatchlings may overwinter in the nest and emerge the following spring (Ernst et al. 1994; Hammerson 1999). Individuals may live up to 50 years (based on rates of growth and observed carapace size), with ten-year old females having a carapace length of about 25 cm, and carapace length of ten-year old males about 16 cm; the oldest female on record (a captive zoo animal) lived 25 years.
Montana populations of the Spiny Softshell are poorly understood, making management of them more difficult. It is apparent that the construction of dams and large reservoirs on rivers (e.g. Fort Peck Dam and Reservoir) is detrimental to population continuity, effectively creating smaller isolated populations. Impacts of other habitat disturbances are not clear. Studies of nesting success, population structure, dispersal, and population size need to be conducted throughout the range of both Montana sub-populations (Missouri River and Yellowstone River). Routine surveys for Spiny Softshells in appropriate habitats could be made a standard part of the field duties of agency fishery biologists. Records should be maintained of the incidental "take" by anglers, who should be encouraged to report any captured Spiny Softshell; killed animals should be examined by agency fishery or wildlife biologists if possible so that data on sex, size, and food habits can be gathered and a base of information on the biology of this species developed. Nesting sites need to be identified and protected from disturbance by human activities.
- Literature Cited AboveLegend: View Online Publication
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- Additional ReferencesLegend: View Online Publication
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