Northern Map Turtle
Graptemys geographica

Common Name:

Northern Map Turtle

Scientific Name:

Graptemys geographica

Etymology:

Genus:

Graptemys is derived from the Greek word grapho which means "write" and emys which means "freshwater tortoise".

Species:

geographica is from the Greek word geo which means "earth" and grapho which means "write". referring to the reticulated pattern on the carapace.

Average Length:

females 7 - 10.8 in. (18 - 27.3 cm), males 3.5 - 6.3 in. (9 - 15.9 cm)

Virginia Record Length:

9.6 in. (24.4 cm)

Record length:

10.8 in. (27.3 cm)

Systematics: Described originally as Testudo geographica by Charles Alexandre LeSueur in 1817, based on a specimen or specimens he saw from a "marsh on border of Lake Erie." Agassiz (1857) was the first to use the genus Graptemys for this species. McDowell (1964) considered Graptemys to be congeneric with Malaclemys and used the combination Malaclemys geographica. This suggestion has not been followed by most of the herpetological community because the evidence was not compelling (Wood, 1977). However, in the Virginia literature, Jopson (1972) and Hardy (1972) used M. geographica. All other Virginia authors have followed the current nomenclature. There are no subspecies.

Description: A large freshwater turtle reaching a maximum carapace length (CL) of 273 mm (10.7 inches) (Conant and Collins, 1991). In Virginia, known maximum CL is 244 mm, maximum plastron length (PL) is 213 mm, and maximum body mass is 1,460 g.

Morphology: Carapace smooth, keeled, and serrated along posterior margin; marginals 12/12, pleurals 4/4, and vertebrals 5; hingeless plastron 85-87% of CL.

Coloration and Pattern: Carapace brown to olive with a pattern of fine yellow reticulations; marginals with yellow reticulations dorsally, but yellow with a circular blotch ventrally; bridge with longitudinal yellow and dark-olive lines; plastron immaculate yellow that fades to cream in old adults; transverse seams of plastral scutes lined in black in small individuals; skin brown to olive with thin yellow stripes; head and neck abundantly striped in yellow; there is a somewhat triangular, yellow patch behind the eye; surfaces of upper and lower jaw yellow; limbs patterned with yellow stripes dorsally and ventrally.

Sexual Dimorphism: This species exhibits strong sexual dimorphism. Males from Virginia are small, averaging 96.9 ± 14.4 mm CL (75.7-132.1, n = 20), 82.4 ± 11.0 mm PL (66.5-102.9, n = 20), and 106.7 ± 42.1 gbody mass (58-232, n = 19). Females are large, averaging 206.9 ± 33.7 mm CL (145.0-244.0, n = 7), 179.0 ± 27.4 mm PL (127.4- 213.0, n = 7), and 1,052.7 ± 408.5 g body mass (410-1,460, n = 7). Sexual dimorphism index was 1.13. The carapace of males is oval and tapers posteriorly, and the anal opening extends beyond the posterior edge. Male foreclaws are not elongated. In females, the carapace is rounded and the anal opening does not extend beyond the posterior margin. The precloacal length in males was 10-35 mm (ave. = 26.8 ± 6.2,n = 19) and in females was 16-30 mm (ave. = 24.7 ± 4.7, n = 7).

Juveniles: Juveniles are colored and patterned as adults. The carapace is rounded for the first 1-2 years of life. CL for 13 Virginia hatchlings was 30.7-33.4 mm (ave. = 32.1 ± 0.8), PL was 27.9- 37.1 mm (ave. = 28.9 ± 0.8), and mass averaged 8.0 g.

Confusing Species: Northern Map Turtles may be confused with Chrysemys picta, Pseudemys concinna hieroglyphica, and Trachemys scripta troostii in their Virginia range, especially when viewed from a distance. Chrysemys picta have conspicuous transverse, light markings on the unkeeled carapace, and 2 yellow spots behind the eye. Sliders have a narrow yellowish, elongated patch behind each eye, broad chin stripes, and a yellow streak in each pleural scute. Cooters have thin yellow lines on a dark head and neck; no spots or patches lie behind the eyes.

Geographic Variation: None in Virginia.

Biology: Northern Map Turtles are riverine animals inhabiting creeks and rivers in the Ridge and Valley region of southwestern Virginia. They occur in lentic water and in riffles; they have not been reported from impoundments. Pluto and Beilis (1986) found that most large Northern Map Turtles in Pennsylvania were found in slow, deep water, and small turtles in slow, shallow water. Although they are most conspicuous when basking, Northern Map Turtles can be seen in the water from bridges and can be caught by turning over rocks. They are a commonly seen turtle in riverine habitats in southwestern Virginia. The primary activity season in Pennsylvania extends from April to December (Pluto and Beilis, 1986). Hibernation occurs under rocks and ledges in deep, slow water (Pluto and Beilis, 1988), although overhanging banks and muskrat burrows are undoubtedly used. Terrestrial activity seldom occurs, except in the nesting season.

The primary prey of this turtle are freshwater mollusks. In a Wisconsin study, Vogt (1981a) found the following prey in decreasing order of volume: mollusks, fish (carrion), mayfly larvae, damselfly larvae, vegetation, and caddisfly cases. Additional prey types are crayfish and beetles (Lagler, 1943). The freshwater snails Leptoxis subglobossa and Oxytrema simplex and a mayfly larva have been identified from Virginia turtles. All feces of turtles I captured contained parts of snail shells. Predators of this species have not been recorded. Humans kill an unknown number each year by beheading turtles caught on fishing lines (J. C. Mitchell, pers. obs.). Eggs in nests are probably eaten by raccoons (Procyon lotor) and skunks (Mephitis, Spilogale). Vogt (1981b) reported mortality of eggs from infestation by fly larvae (maggots) in Wisconsin.

The reproductive cycle of this species has not been studied. Mating occurs in late summer and fall (Pluto and Beilis, 1988) and females nest late May to mid-July (Ernst and Barbour, 1972). Three Virginia females contained oviductal eggs when examined on 16 June. The smallest mature female was 186 mm PL. The smallest mature male in the Virginia sample measured 67 mm PL. Females apparently produce up to two clutches per year as evidenced by the presence of oviductal eggs and enlarged follicles in three females. Clutch size in Virginia was 13-16 (ave. = 15.0 ± 1.7, n = 3). Egg size averaged 35.0 ± 1.0 x 21.3 ± 0.9 mm (length 33.2-36.6, width 19.5-22.4, n = 29) and weighed 8.1-9.8 g (ave. = 9.0, n = 2). A single clutch hatched on 4-6 September after a 74-day incubation period in the laboratory. Hatchlings were found to overwinter in the nest in Iowa (Christiansen and Galloway, 1984).

Nothing is known about the ecology of G. geographica populations in Virginia. In a Wisconsin study, Vogt and Bull (1984) showed that nest location in different microhabitats affects sex ratios of emerging hatchlings, as low nest temperatures (23-28°C) produce males and high nest temperatures (30-35°C) produce females. Length of home ranges in a Pennsylvania river was 170-6,070 m for males and 0-5,290 m for females (Pluto and Beilis, 1988). Movements along the river were associated with summer foraging and nesting behavior.

Northern Map Turtles are wary baskers and will dive off basking sites with little provocation. Several turtles will often bask close to or on top of one another and, when one dives in, the rest will follow. Large turtles will often physically displace smaller ones at the most used basking sites, and large ones will bask farther away from shore than small ones (Pluto and Beilis, 1986).

Remarks: Wood (1977) speculated that Graptemys is absent from the Coastal Plain rivers from Virginia to Florida because these rivers carry large silt loads that reduce the quality of the habitat for this species and its molluscan prey.

Because Northern Map Turtles prey almost exclusively on mollusks, their impact on the many endangered species in that group is worthy of study. Do Northern Map Turtle populations need management in areas of high mollusk diversity?

Conservation and Management: Northern Map Turtle populations appear to be reasonably viable in southwestern Virginia. This species was listed as status undetermined by Mitchell and Pague (1987) and Mitchell (1991a). The rivers of the upper Tennessee drainage have been impacted by pollution of various kinds, and the threat continues. It is likely that Northern Map Turtle are affected by the consumption of pollutants in the tissues of their prey. Any adverse environmental impact on freshwater mussels is likely to indirectly impact Northern Map Turtle. Additional inventories and population studies are needed to ascertain whether active management is necessary.

References for Life History

Photos:

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Verified County/City Occurrence

Hampton City
Lee County
Prince William County
Russell County
Scott County
Smyth County
Tazewell County
Washington County
Verified in 8 Counties/Cities.



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