Spiny softshell turtle (Apalone spinifera)

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Spiny softshell turtle, front view
IUCN Red List species status – Least Concern LEAST
CONCERN

Top facts

  • The spiny softshell turtle is an unusual-looking freshwater turtle with a round, flat, pancake-like shell.
  • Unlike the hard shell of most other turtles, the shell of the spiny softshell turtle is soft and leathery, with a sandpaper-like surface.
  • The spiny softshell turtle spends most of its life in water, often lying buried in the sandy or muddy bottom with only its head and neck protruding.
  • In parts of its range, the spiny softshell turtle hibernates in the bottom mud for around six months of the year.
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Spiny softshell turtle fact file

Spiny softshell turtle description

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderTestudines
FamilyTrionychidae
GenusApalone (1)

The spiny softshell turtle (Apalone spinifera) is a medium to large freshwater turtle species with an unusually flat, round, leathery shell. The front edge of the upper shell, or carapace, bears small spines, while the surface of the shell is covered with soft skin and has a sandpaper-like texture (2) (4) (5) (7) (8).

This species has a distinctive tubular snout, which ends in large nostrils (4) (7) (8). The spiny softshell turtle’s feet are webbed, and the webbing on the hind feet extends onto the hind limbs (4) (8). Each foot bears three claws (5).

The carapace of the spiny softshell turtle is usually an olive to yellowish-brown colour, patterned with black, eye-like spots or dark blotches, and with a dark line around the outer edge (2) (3) (4) (5) (7). The lower shell, or plastron, is typically white or yellow (7), while the head and limbs are olive to grey with dark spots (3) (4) (7) (8). The spiny softshell turtle’s head is marked with two pale lines which are bordered with black and extend backwards from the eye and jaw (4) (7).

Juvenile spiny softshell turtles resemble the adult male in appearance, but adult females generally lose their black spots and instead develop a mottled or blotched pattern with age (2) (4) (5) (7) (8). Adult females are also much larger than males, and have a relatively short tail in comparison to the long, thick tail of the male (2) (4). In addition, the female’s shell may have a smoother texture than the male’s (2) (3).

A number of subspecies of spiny softshell turtle are recognised, which vary slightly in their markings. Some subspecies also have small white spots on the carapace (2) (7).

Also known as
black spiny softshell, Cuatro Cienegas softshell, eastern spiny softshell, Guadalupe spiny softshell, Gulf Coast spiny softshell, pallid spiny softshell, spiny softshell, Texas spiny softshell, western spiny softshell.
Synonyms
Amyda spinifera, Apalone hudsonica, Aspidonectes asper, Aspidonectes emoryi, Platypeltis agassizii, Trionyx ater, Trionyx spinifer, Trionyx spiniferus.
Size
Male carapace length: 12.5 - 23.5 cm (2) (3)
Female carapace length: 18 - 54 cm (2) (3)
Hatchling carapace length: 3 - 4.4 cm (4)
Female weight: up to 12 kg (3)
Hatchling weight: 8 - 10 g (5)
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Spiny softshell turtle biology

The spiny softshell turtle is mainly carnivorous, feeding on crustaceans such as crayfish, as well as insects, small fish, worms, molluscs, tadpoles and frogs (1) (4) (5) (7) (9). It also occasionally eats some plant material, though possibly by accident (7). The spiny softshell turtle may actively hunt along the bottom of its watery habitat, searching for prey beneath objects or in clumps of vegetation, or it may conceal itself in the bottom mud and ambush passing prey (5).

This species spends almost its entire life in water, and often lies buried in the soft bottom with only its head and neck protruding into the water column. The spiny softshell turtle often buries itself in shallow water where its nostrils can reach the surface (2) (4) (7), but it will also bury itself in deeper water (4) (7). This turtle has a remarkable ability to extract oxygen from the water through its skin, allowing it to stay underwater for extended periods (4). The spiny softshell turtle also frequently basks on shore, on floating logs or on rocks, helping it to regulate its body temperature (5) (8) (9).

In parts of its range, the spiny softshell turtle hibernates in winter, burying itself in the bottom substrate in areas of deep, well-oxygenated water where it is at less risk of freezing (3) (5) (8). In Canada, this species hibernates for around six months of the year, typically emerging again in early May (5).

The spiny softshell turtle usually mates in the spring, with most nests being built around June and July (1) (3) (7) (8) (9). The female typically digs the nest in an open, sunny area of sand, gravel or soil close to water (5) (8) (9), and the eggs have hard shells which help to prevent them drying out (3). Each clutch consists of around 4 to 32 white eggs (5) (7), and females may sometimes lay two clutches a year (1) (7) (8) (9). The young turtles hatch from August to October (5) (7) (9). Unusually among turtles, the sex of the spiny softshell turtle hatchlings is not dependent on the temperature at which the eggs were incubated (4) (7) (10).

The male spiny softshell turtle is reported to reach sexual maturity at a shell length of just 9 to 10 centimetres, whereas the female matures at a shell length of around 18 to 20 centimetres (5), when it is approximately 12 years old (3) (5). The eggs and young of the spiny softshell turtle are vulnerable to a range of predators, including raccoons and foxes, as well as to infestation by fly maggots (3) (5) (8). However, adults of this species have few natural predators and are thought to potentially live to over 50 years old (5).

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Spiny softshell turtle range

The spiny softshell turtle is found across a large part of North America, from southernmost Ontario and Quebec in Canada, through most of the United States east of the Rocky Mountains, and as far south as the Gulf Coast of Mexico (1) (3) (7) (9). This species has also been introduced in some U.S. states, such as New Jersey and Virginia (7) (9).

In Canada, the spiny softshell turtle formerly occurred throughout the Great Lakes-St Lawrence watershed, but is now found only in two isolated populations in this area (3) (8). Each subspecies of the spiny softshell turtle occupies a slightly different geographical range, and that of the Cuatro Cienegas softshell (A. s. atra) is particularly restricted, being confined to the Cuatro Cienegas basin of Coahuila, Mexico (1).

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Spiny softshell turtle habitat

A highly aquatic species, the spiny softshell turtle lives in a variety of freshwater habitats, including fast-flowing rivers, lakes, creeks, ponds and even ditches. It appears to require water bodies with a soft bottom and some aquatic vegetation, as well as open sandy or muddy banks for basking and nesting (1) (2) (3) (7) (8) (9).

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Spiny softshell turtle status

The spiny softshell turtle is classified as Least Concern (LC) on the IUCN Red List and the Cuatro Cienegas softshell (subspecies Apalone spinifera atra) is listed as Critically Endangered (CR) (1). The Cuatro Cienegas softshell is also listed on Appendix I of CITES (6).

IUCN Red List species status – Least Concern

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Spiny softshell turtle threats

The spiny softshell turtle is widespread and generally quite common (1) (9). However, although the species as a whole is not currently considered to be threatened, some populations and subspecies face a number of localised threats, including bycatch by fishermen, collisions with boats, pollution, water diversion and the building of water infrastructure (1) (3) (5) (8) (11) (12). In some areas, this species has also been caught as food (4).

The isolated populations of spiny softshell turtles in southern Canada and Vermont are considered to be threatened by extensive habitat loss and degradation, mainly through development and recreation, which disturb or damage the species’ nesting, feeding, basking and hibernation sites (3) (5) (8) (12).

Human activities may also have increased the populations of raccoons and other species which predate the nests of the spiny softshell turtle, while environmental pollutants could be a further cause of nest failure (8). Adult spiny softshell turtles are thought to be particularly sensitive to pollution due to their fairly permeable shells. Other potential threats to the spiny softshell turtle include the legal and illegal trade in pet turtles, which can result in the release of captive turtles into the wild and increase the risk of disease transmission to wild populations (5).

The Cuatro Cienegas softshell (subspecies A. s. atra) is found in a very restricted area in Mexico, where it is under threat from changes to the water system, including the building of irrigation systems and the digging of canals. This subspecies is also threatened by the building of infrastructure for industry, tourism and recreation (1).

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Spiny softshell turtle conservation

Across its large range, the spiny softshell turtle occurs in a number of sites and habitats under various degrees of protection (1). In Canada, the spiny softshell turtle is listed as Threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), which determines the status of species that are considered to be at risk in the country (12). This species is also protected under the Species at Risk Act (SARA) (3).

Some of the spiny softshell turtle’s nesting sites in Canada are protected (3) (8), although high levels of recreational activity are still a problem at some locations (3). The Nature Conservancy of Canada (NCC) is undertaking a number of conservation measures for the spiny softshell turtle, including habitat protection, nest monitoring and educational activities (13).

In Vermont, a recovery plan for the spiny softshell turtle outlines a number of recommended conservation measures, including protecting and improving its habitat, and raising public awareness of this unusual reptile. A number of studies have been done into the species’ movements and habitat use, while trapping of predators and fencing of nests has been used to try and increase nesting success (5).

The Cuatro Cienegas softshell (A. s. atra) is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), meaning that international trade in this subspecies is prohibited (6). It is also protected under national legislation in Mexico, and its entire range is within the Cuatro Cienegas Flora and Fauna Protection Area (1).

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Find out more

Find out more about the spiny softshell turtle and other turtle species:

More information on turtle conservation:

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Glossary

Bycatch
In the fishing industry, the part of the catch made up of non-target species.
Carapace
The top shell of a turtle or tortoise.
Carnivorous
Feeding on flesh.
Crustaceans
Diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.
Hibernation
A winter survival strategy in which the animal passes the winter in a resting state. This period of inactivity is characterised by specific biological and biochemical changes including lowered blood pressure and respiration rate. In reptiles, this is also known as brumation.
Incubate
To keep eggs warm so that development is possible.
Molluscs
A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
Plastron
The lower shell of a turtle or tortoise.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
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References

  1. IUCN Red List (August, 2013)
    http://www.iucnredlist.org/
  2. Conant, R. and Collins, J.T. (1998) A Field Guide to Reptiles and Amphibians of Eastern and Central North America. Third Edition. Houghton Mifflin Company, New York.
  3. Government of Canada: Species at Risk Public Registry - Spiny softshell (August, 2013)
    http://www.sararegistry.gc.ca/species/speciesDetails_e.cfm?sid=278
  4. Ernst, C.H. and Lovich, J.E. (2009) Turtles of the United States and Canada. Second Edition. The Johns Hopkins University Press, Baltimore.
  5. Vermont Fish and Wildlife Department (2009) Vermont Eastern Spiny Softshell Turtle Recovery Plan. Vermont Fish and Wildlife Department, Waterbury. Available at:
    http://www.vtfishandwildlife.com/library/reports_and_documents/nongame_and_Natural_Heritage/Recovery%20Plans/Eastern_Spiny_Softshell_Turtle_Recovery_Plan.pdf
  6. CITES (August, 2013)
    http://www.cites.org/
  7. Ernst, C.H., Altenburg, R.G.M. and Barbour, R.W. (1997) Turtles of the World. ETI Information Systems Ltd, Netherlands. Available at:
    http://wbd.etibioinformatics.nl/bis/turtles.php
  8. COSEWIC (2002) COSEWIC Assessment and Update Status Report on the Spiny Softshell Turtle Apalone spinifera in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa. Available at:
    http://publications.gc.ca/collections/Collection/CW69-14-257-2003E.pdf
  9. NatureServe Explorer - Apalone spinifera (August, 2013)
    http://www.natureserve.org/explorer/index.htm
  10. Greenbaum, E. and Carr, J.L. (2001) Sexual differentiation in the spiny softshell turtle (Apalone spinifera), a species with genetic sex determination. Journal of Experimental Zoology, 290: 190-200.
  11. Galois, P. and Quellet, M. (2007) Traumatic injuries in eastern spiny softshell turtles (Apalone spinifera) due to recreational activities in the northern Lake Champlain basin. Chelonian Conservation and Biology, 6(2): 288-293.
  12. Committee on the Status of Endangered Wildlife in Canada (COSEWIC) - Spiny softshell (August, 2013)
    http://www.cosewic.gc.ca/
  13. Nature Conservancy Canada - Spiny softshell turtle (August, 2013)
    http://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/spiny_softshell_turtle.html
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Spiny softshell turtle, front view  
Spiny softshell turtle, front view

© Rolf Nussbaumer / naturepl.com

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