|
Canadian Herpetological Society Société d'Herpétologie du Canada |
|---|
 credited.jpg){kind=link}
Northern Map Turtle
Graptemys geographica
Family: Emydidae
COSEWIC status:- Special Concern
- Special Concern
- Least Concern
Description
The Northern Map Turtle gets its name from the markings on its shell, which resemble the contour lines on a topographical map. The carapace (upper shell) is olive green with fine yellow lines and has a distinct keel (ridge) along the centre and serrations along the rear edge. The head and legs are olive, brown or black with yellow lines. The plastron (lower shell) is mainly a uniform colour ranging from cream to yellow. Females can reach 27 cm in carapace length, whereas males rarely exceed 16 cm carapace length and have proportionately smaller heads. Hatchlings have a carapace length of 2.5–3.5 cm and resemble the adults in colour and pattern.
Similar Species
The Painted Turtle has similar markings on the head and legs, but its carapace lacks a keel, has red markings around the edges, and lacks a serrated rear margin. The exotic Red-eared Slider also has yellow markings on the head and legs, and sometimes a pattern on the carapace, but it lacks the serrated rear margin of the carapace and usually (but not always) has a red stripe behind the eye.
Distribution
Click for larger image
The Canadian range of the Northern Map Turtle is limited to southern Ontario and a small portion of southwestern Quebec. In the United States, it occurs from Minnesota in the west to Vermont in the east and as far south as Arkansas and Alabama.
Habitat
The Northern Map Turtle is usually found in large water bodies such as rivers and lakes, particularly in areas with slow-moving water and abundant basking sites. Nesting sites are typically in sandy, open-canopy habitats within a few hundred metres of water. Individuals overwinter at the bottom of lakes and rivers.
Biology
In Canada, Northern Map Turtles are dormant during the winter and are typically active from April until early October. Females typically nest in late May or June. The female excavates a nest cavity and deposits 3–22 elliptical eggs. Hatchlings emerge in late August or September or may overwinter in the nest. The sex of the offspring depends on incubation temperature; warmer incubation temperatures produce females and cooler temperatures produce males. Female Northern Map Turtles require 12 years to reach sexual maturity in Canada, while males mature after 4 years. Females may lay two clutches of eggs in some years. Maximum longevity is unknown, but individuals can live for more than 20 years. Given their difference in size, males and females often feed on different prey, with females consuming more mussels and males eating more snails, insects and smaller crustaceans. Individuals can make substantial movements throughout the active season, and home range lengths are 2–24 km, with females moving greater distances.
Threats
Northern Map Turtles appear to be sensitive to poor water quality, possibly because of its effect on prey abundance. Shoreline development and “hardening” can eliminate basking and nesting habitat, and loss of shoreline habitat is one of the primary threats to this species. Females are vulnerable to traffic mortality when travelling over land in search of nesting sites, and mortality from boat propeller strikes and fishing by-catch likely contribute to unsustainable rates of adult mortality in some areas. High volumes of boat traffic can also reduce overall habitat quality by regularly disrupting basking or nesting behaviour. Nest predation by subsidized predators (e.g. Raccoon, Skunk) and illegal collection for the pet trade or for human consumption also threaten some populations, and climate change poses a potentially serious future threat to Canadian Turtles