Species accounts

Snapping turtle

Chelydra serpentina

TAXONOMY

Testudo serpentina Linnaeus, 1758, "Calidus regionibus" (warm regions). Two subspecies are recognized.

OTHER COMMON NAMES

English: Common snapping turtle; snapper; French: Chélydre serpentine; German: Schnappschildkröte; Spanish: Tortuga-lagarto común.

PHYSICAL CHARACTERISTICS The carapace of these large turtles, to 19.3 in (49 cm), bears three low, knobby keels (except in the oldest individuals). The shell is dark, although it may range from brown to olive to black. The head is large, the upper jaw is somewhat hooked anteriorly, and the eyes open dorsolaterally (toward the top and side of the head).

DISTRIBUTION

Ranges extend from southern Canada across the United States east of the Rocky Mountains to New Mexico, Texas, and

I Chelydra serpentina I Macrochelys temminckii

Florida. Tropical snapping turtle populations (until recently considered subspecies of the snapping turtle) range from Veracruz, Mexico, through Central America to western Ecuador in northwestern South America.

HABITAT

Snapping turtles inhabit nearly any body of freshwater within their range, although they also invade brackish water environments in many areas. They seem to prefer warm, shallow, still water, with soft bottoms and abundant aquatic vegetation.

BEHAVIOR

Snapping turtles are highly aquatic, spending most of their time lying camouflaged in the mud in shallow water. Most active during the morning and early evening, these turtles are often active at night in the south, but rarely so in the north. When active, they are primarily bottom-walkers, slowly moving over the bottom in search of food or mates. Most thermoregulation is done by selecting warm, shallow, submerged sites; however, they occasionally bask by floating on the water's surface or even by climbing out of the water onto emergent logs or other objects. They may be active year-round in the south, but hibernate for half the year or more in the north. However, some individuals may be active in the north in midwinter under thick ice cover. In addition to nesting forays by females, snappers frequently travel great distances overland between bodies of water (often almost a mile). They also make equally impressive movements in the water, one observed female moved 2.1 mi (3.4 km) in just 10 days.

FEEDING ECOLOGY AND DIET

Although snapping turtles are probably carnivorous by preference, they can subsist on diets ranging from completely carnivorous to completely herbivorous. Animal foods include sponges, flatworms (planarians), earthworms, leeches, clams, snails, crustaceans, spiders, insects, amphibians and their eggs and larvae, snakes, other turtles, birds, small mammals, and carrion. Snapping turtles also eat algae, duckweed, and other submergent and emergent aquatic plants and their seeds.

REPRODUCTIVE BIOLOGY

Mating is known to occur from April to November, but probably peaks in the spring and fall. Courtship is highly variable, from the male directly mounting the female from behind, to the male trailing along after the female for several minutes before mounting, to face-offs, head-swaying, and/or water gulping and belching before mounting. Eventually the male mounts atop the female's shell and swings his tail under hers to mate. At high latitudes, nesting begins in early June and may extend to early July, whereas at low latitudes it may extend from late April to early June. Females may nest within a few feet of the water's edge or travel overland as far as 9.9 mi (16 km) to nest. The nest is dug (and covered) with the hind feet, and because of its size and depth (to 9.8 in [25 cm]), even a covered nest is quite obvious. Consequently, nests are heavily predated by animals, most within 24 hours of construction.

Females produce at most one clutch per year, with some females apparently skipping some years. They lay spherical, hard-shelled eggs that average 1.1 in (2.8 cm) in diameter and 0.4 oz (11 g) in mass. Egg size does not seem to increase significantly with female size. Clutch size is highly variable, rang

Chelydra serpentina

ing from six to 109, averaging about 32 across the range, and is positively correlated with female body size, latitude, longitude, and elevation (the largest clutches are laid in western Nebraska). Incubation in nature requires 55-125 days (more typically 75-95) depending on nest temperature (development being faster at higher temperatures) and geography (incubation times being longer in the south). Hatchling snapping turtles usually emerge from the nest in the late summer and fall (August to October) and move directly to the water. Hatchlings in northern populations that do not emerge in the fall before the onset of cold weather almost never survive the winter, probably because of their low tolerance of subfreezing body temperatures. High and low incubation temperatures result in the production of all-female offspring, and intermediate temperatures produce all males. Because their clutches are so large, eggs in different parts of the same nest may produce different sex ratios, e.g., all females at the top and all males at the bottom.

CONSERVATION STATUS

This species has such an extensive range and is so prolific that it has so far been able to persist even in habitats significantly altered by humans.

SIGNIFICANCE TO HUMANS

Snapping turtles are exploited by humans primarily for their meat, although some small individuals make their way into the pet trade. ♦

Alligator snapping turtle

Macrochelys temminckii

TAXONOMY

Chelonura temminckii Harlan, 1835, tributary stream of the Mississippi, which enters the river above Memphis, in west Tennessee. No subspecies are recognized.

OTHER COMMON NAMES

English: Alligator snapper; French: Macroclemyde de Temminck; German: Geierschildkröte.

PHYSICAL , CHARACTERISTICS

Alligator snapping turtles are the largest freshwater turtles in North America (up to 31.5 in [80 cm]; 250 lb [113 kg]). The carapace bears three prominent knobby keels. The head is very large, has a strongly hooked beak, and eyes that open laterally (toward the side of the head). Three to eight small supramarginal scutes are present laterally between the marginal and pleural scutes. The turtles have a pink, wormlike projection on the tongue, which they can wriggle to lure prey.

DISTRIBUTION

Snapping turtles occur in the Gulf of Mexico drainages in the southeastern United States.

HABITAT

These turtles are primarily found in rivers and large streams, but also in lakes, ponds, swamps, and even brackish water.

BEHAVIOR

Alligator snapping turtles are highly aquatic, almost never leaving the water except to nest. They are capable of making extremely long underwater movements, up to 4.2 mi (6.8 km) in a week, or to 18.7 mi (30 km) or more over several years.

FEEDING ECOLOGY AND DIET

These turtles are primarily carnivorous. In addition to luring fish with their tongue, they also eat crayfish, crabs, clams, snails, salamanders, turtles, snakes, small alligators, birds, and mammals, as well as plant roots, fruits, and seeds (e.g., grapes and acorns).

REPRODUCTIVE BIOLOGY

Mating may occur in the spring or the fall. Courtship is poorly developed and males climb onto the female's shell from behind for mating. Nesting occurs between late April and early June, and most nests are laid within 236 ft (72 m) of the water. The eggs are spherical and 1.3-1.6 in (3.3-4.1 cm) in diameter. Females lay a single clutch each year of nine to 61 eggs (about 35 being typical), larger females producing larger clutches. Laboratory incubation of eggs to hatching requires 79-113 days, depending on temperature. Warm incubation temperatures result in the production of all females, low incubation temperatures produce nearly all females, and intermediate temperatures produce mostly males.

CONSERVATION STATUS

Alligator snapping turtles have declined significantly due to overharvesting, and hence are cited as Vulnerable on the IUCN Red List.

SIGNIFICANCE TO HUMANS

Humans heavily exploit these turtles for their meat, and hatch-lings are produced for the pet trade. ♦

Resources

Books

Pritchard, P. C. H. The Alligator Snapping Turtle, Biology and Conservation. Milwaukee: Milwaukee Public Museum, 1989.

Periodicals

Congdon, J. D., A. E. Dunham, and R. C. van Loben Sels. "Demographics of Common Snapping Turtles (Chelydra serpentina): Implications for Conservation and Management of Long-Lived Organisms." American Zoologist 34, no. 3 (1994): 397-4Q8.

Ewert, M. A., and D. R. Jackson. "Nesting Ecology of the Alligator Snapping Turtle (Macroclemys temminckii) along the Lower Apalachicola River, Florida." Florida Game and Fresh Water Fish Commission Non-Game Wildlife Program Final Report (1994): 1-45.

Resources

Iverson, J. B., H. Higgins, A. G. Sirulnik, and C. Griffiths. "Local and Geographic Variation in the Reproductive Biology of the Snapping Turtle (Chelydra serpentina)." Herpetologica 53 (1997): 96-117.

"Conservation Genetics of the Common Snapping Turtles

(Chelydra serpentina)." Conservation Biology 10 (1996): 397-405.

Walker, D., P. E. Moler, K. A. Buhlmann, and J. C. Avise. "Phylogeographic Uniformity in Mitochondrial DNA of the Snapping Turtle (Chelydra)." Animal Conservation 1 (1998): 55-60.

John B. Iverson, PhD

Central American river turtles

(Dermatemydidae)

Class Reptilia Order Testudines Suborder Cryptodira Family Dermatemydidae

This is a large aquatic turtle whose dark shell appears leathery in adults, whose plastron and bridge are both large, and whose head is relatively small with a pointed snout; a row of inframarginal scutes separates the scutes of the carapace from those on the plastron

Size

Up to 26 in (65 cm) and 49 lb (22 kg)

Number of genera, species

1 genus; 1 species

Habitat

Permanent rivers and lakes

Endangered

Caribbean Sea and Gulf of Mexico drainages of Mesoamerica

Evolution and systematics

These river turtles (Dermatemys mawii) are most closely related to the mud and musk turtles (family Kinosternidae). The fossil record of this family is extensive, with the earliest material being from the Lower Cretaceous in Asia, and abundant remains in North and Central America, Europe, and Africa during the Tertiary. The Central American river turtle is also commonly known as hickety (Belize), jicotea, tortuga aplanada (Mexico), tortuga blanca (Mexico, Guatemala), and tortuga plana (Mexico). No subfamilies are recognized.

The taxonomy of this species is Dermatemys mawii Gray, 1847, South America (in error); restricted to Alvarado, Veracruz, Mexico, by Smith and Taylor, 1950.

Physical characteristics

These large turtles (up to 49 lb [22 kg]) have a low, dark, carapace that is unicarinate in juveniles, but smooth and leathery in adults. Females reach larger sizes than males. The posterior margin of the shell is smooth and not serrated. The yellow or cream-colored plastron is large, unhinged, and connected to the carapace by a broad bridge on which four or five inframarginal scutes are located (separating the plastral from the carapacial scutes). The snout is pointed, no chin barbels are present, and the toes are strongly webbed. The top of the head in adult males is yellowish and that in adult females and juveniles is gray.

Central American river turtle (Dermatemys mawii). (Illustration by Bruce Worden)

Distribution

Atlantic lowlands from southern Veracruz in Mexico through the southern Yucatán Peninsula, northern Guatemala, and Belize.

Habitat

Permanent water in rivers and large freshwater lakes, occasionally entering brackish water as evidenced by the finding of barnacles on some individuals.

Behavior

This turtle is highly aquatic, is capable of remaining submerged for very long periods, and has a very difficult time moving on land. It is primarily nocturnal, but it can sometimes be seen basking at the surface of the water during the day. It does not bask out of the water.

Feeding ecology and diet

It is almost completely herbivorous, feeding on fruits (e.g., figs), aquatic grasses, and fallen leaves. Insects, fish, and mol-lusks are occasionally consumed.

Reproductive biology

Courtship and mating apparently occur from March to September, and nesting occurs primarily during the rainy season, from late September to December. However, nesting sometimes occurs from late August to March or April. Females produce one to four clutches per year, with two being usual. Nests are excavated in the soil, usually within 10 ft (3 m) of the water, and are often inundated by rising water. Eggs have been found to be viable after being submerged for up to 28 days. Eggs are brittle-shelled, oblong, 2.1-2.8 in X 1.2-2 in (54-72

mm X 30-50 mm), and weigh 1.2-2.5 oz (34-70 g). Clutch sizes range from two to 20, with eight to 14 being typical. Large females have greater annual reproductive potential than small females. Incubation requires seven to 10 months, and hatching occurs in late May through July, at the beginning of the next rainy season. The sex is determined by nest temperature during the middle third of incubation, with high temperatures producing females and low temperatures producing males.

Conservation status

Listed as Endangered on the IUCN Red List, as Endangered by the U.S. Fish and Wildlife Service, and in Appendix II of the CITES.

Significance to humans

Central American river turtles are intensively exploited for food by indigenous peoples throughout their range, even in areas where the species is legally protected. The flesh is considered a delicacy.

Central American river turtle (Dermatemys mawii) in Tabasco, Mexico. (Photo by Jean-Gérard Sidaner/Photo Researchers, Inc. Reproduced by permission.)

Resources

Books

Lee, Julian C. The Amphibians and Reptiles of the Yucatán Peninsula. Ithaca, NY: Comstock, 1996.

Polisar, John. "Effects of Exploitation on Dermatemys mawii Populations in Northern Belize and Conservation Strategies for Rural Riverside Villages." In Proceedings: Conservation, Restoration, and Management of Tortoises and Turtles: An International Conference, 11 to 16 July 1993, State University of New York, Purchase, New York, edited by Jim Van Abbema. Bronx, NY: New York Turtle and Tortoise Society, 1997.

Periodicals

Polisar, John. "Reproductive Biology of a Flood-Season Nesting Freshwater Turtle of the Northern Neotropics: Dermatemys mawii in Belize." Chelonian Conservation and Biology 2, no. 1 (1996): 13-25.

Polisar, J., and R. H. Horwich. "Conservation of the Large, Economically Important River Turtle Dermatemys mawii in Belize." Conservation Biology 8, no. 2 (1994): 338-340.

Vogt, R. C., and O. Flores-Villela. "Effects of Incubation Temperature on Sex Determination in a Community of Neotropical Freshwater Turtles in Southern Mexico." Herpetologica 48, no. 3 (1992): 265-270.

John B. Iverson, PhD

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