Northern Map Turtle (Graptemys geographica)

Common Map Turtle
Graptemys geographica

by Jeff LeClere


Louisa Co., IA


Plastron, Louisa Co.

Key to Similar Species

Status

PROTECTED, except from the Mississippi River and its connected backwaters. Here, it is legal to take with a valid fishing license. These turtles may be trapped, or taken by hand, hook and line, or turtle hook. The possesion limit 100 pounds for live and 50 pounds for dressed turtles.

Description

This is a medium to large sized Iowa turtle that grows 6 to 10 inches carapace length. The shell is dark brown, olive, or black. This turtle gets its name from the light yellow lines that form a reticulated or map like pattern on the back, but this pattern is usually obscure on adults. Old females have dark blotches on the back. There is a low vertebral keel on the back that becomes less prominent with age. The marginals on the rear of the carapace are serrated. The plastron is dull yellow with some black or dark pigment. The head and limbs are black or dark olive. There are light lines on the head and limbs that also form a map like pattern. A small, solid yellow dot present behind each eye (these are the only dots or spots found on the head) distinguishes common map turtles from all our other map turtles.

Females grow much larger than the males. Adult females have a low keel on the back, large heads, and a light upper lip. Adult males have a pronounced keel on the back, dark upper lips, long claws on the front feet, and a long, thick tail with the cloacal opening past the edge of the carapace.Young have brighter shells and markings, a dark pattern on the plastron, and a pronounced vertebral keel.

Subspecies

None.

Range

The common map turtle has been documented along the Mississippi River and tributaries in extreme eastern Iowa.

Habitat

This turtle is found only in slow portions of larger rivers in Iowa. Lakes and oxbow ponds are utilized only when close to a good sized river. They do not travel as far from the Mississippi River in eastern Iowa as the false map turtle, Graptemys pseudogeographica.

Habits

Common map turtles have a shorter active season when compared to other Iowa turtles. They are active from April to September. They are diurnal and spend a considerable amount of time basking. They forage in the water for short periods during the day. They are very aquatic and do not roam far from water. They bask on anything above the water as long as it is away from shore in deep water. Snags and fallen trees with many limbs provide ideal basking areas and a large number of turtles may bask at this site. Approach very slowly and quietly as these turtles are extremely wary. If one dives, they all dive. The turtles remaining (if any ) are the painted turtles. They resurface fairly quickly, but will remain very cautious and in the water until the danger has past.

Map turtles breed in spring, and females nest in late May through June. They usually do not migrate long distances to lay eggs. Females may nest on overcast days with light rain (Oldfield and Moriarty, 1994). Females may dig a few false nests before actually depositing 12 to 20 eggs. They often nest on sand bars, where possible. The young emerge in August or September or they may overwinter in the nest (Vogt, 1981). They mature at about 14 years of age (Ernst, Lovich, and Barour, 1994).

Food

Common map turtles eat primarily snails and clams. They usually crush them in their powerful jaws, but small ones are sometimes swallowed whole. Additional foods include crayfish, aquatic insect larvae, fish, and a few aquatic plants. They are found together with many other aquatic turtle species, including the two other map turtle species in Iowa. To avoid competition, this turtle preys heavily on mollusks while the other species prefer other prey (Vogt, 1981b).