"Herps of the Southeast" Virtual Walk
East Aiken Elementary has completed walk...
Page Under Revision
|
Stop
30 —
|
Featured Herp
Map Turtles |
Map Turtles
(Graptemys spp.)
|
Map turtles on the Conecuh We had been on the river for a full day and didn’t have a single map turtle
to show for our efforts. Sure we had seen plenty, but the shy denizens of
the Conecuh River in southern Alabama eluded our attempts to capture them
every time. Motoring upstream in our johnboat we crossed a shoal and saw a
turtle furiously making its way against the current trying to flee our
approaching craft. Tony and I jumped into the river and quickly captured a
large adult female cooter turtle while Josh drifted downstream in the
boat, abandoned by his crew. After releasing the cooter and swimming back
to the boat we renewed our efforts to capture map turtles. |
|
| The United States is home to 13 species of map turtles, or sawbacks, as some species are called in the southern U.S. Map turtles are so named because of the intricate map-like designs, or hieroglyphics, created by patterns on their upper shell or carapace. The scientific name for their genus, Graptemys, literally means “map turtle” in Greek. Most species of map turtles live in the southeastern U.S. with several extending up the Mississippi River into the Great Lakes Region. One species, the common map turtle, lives as far east as the St. Lawrence River and the Delaware and Susquehanna Rivers. A list of the species recognized by herpetologists is shown here with scientific and common names. | Graptemys
geographica, Common Map Turtle Graptemys barbouri, Barbour's Map Turtle Graptemys pulchra, Alabama Map Turtle Graptemys ernsti, Escambia Map Turtle Graptemys gibbonsi, Pascagoula Map Turtle Graptemys caglei, Cagle's Map Turtle Graptemys kohnii, Mississippi Map Turtle Graptemys pseudogeographica, False Map Turtle Graptemys ouachitensis, Ouachita Map Turtle Graptemys versa, Texas Map Turtle Graptemys oculifera, Ringed Map Turtle Graptemys flavimaculata, Yellow-blotched Map Turtle Graptemys nigrinoda, Black-knobbed Map Turtle |
Pascagoula Map Turtle (Graptemys gibbonsi) |
The Conecuh River in Alabama and the Pascagoula River in Mississippi are home to the Escambia map turtle, Graptemys ernsti, and the Pascagoula map turtle (G. gibbonsi), respectively. Both species were discovered by a scientist at the Savannah River Ecology Laboratory in the late 1980’s and formally described as new species in a scientific journal in 1992. That a country as well-studied as the United States still has new species of large reptiles like turtles to be found in the late 20th Century shows that there are many discoveries to be made by young ecologists, even in today’s rapidly changing world. |
|
Both turtles were named after famous herpetologists. The scientific name of the Escambia map turtle honors Dr. Carl Ernst of George Mason University and the Pascagoula map turtle is named after Dr. J. Whitfield Gibbons of the University of Georgia, Savannah River Ecology Laboratory. Both map turtles also show sexual size dimorphism with adult females being much larger than adult males. Females reach a body size of almost 30 cm, while males rarely exceed 12 cm. This condition is not unusual in turtles with many species exhibiting similar differences in male and female body size. Females are likely larger because of the advantage of large size on clutch size: larger females lay more eggs. Since males don’t need this advantage, they mature earlier at a smaller size so that they can begin to reproduce as early as possible. |
|
Life for map turtles is fairly relaxed. They spend long hours basking on logs in the river and intermittently feed on mussels and invertebrates. Males tend to favor the invertebrates with females specializing on mussels. The large jaws and crushing surfaces of the female mouth are special adaptations to this diet. During the night they sleep just below the surface clinging to log jams. |
|
|
Most of what we know of the reproductive ecology of these species is based on research on the Escambia map turtle. The nesting season lasts from late April to late July. Females lay clutches of about 7 eggs and several clutches can be produced in a single year. Nesting takes place at all hours of the day with females constructing flask-shaped nests on sand bars along the river. Eggs hatch after about 75 days and the hatchlings move directly to water after leaving the nest. Hatchling G. gibbonsi emerge from their nests during the first three hours following sunset. Hatchlings range from 34-44 mm in size. The rivers that southern map turtles call home are magnificent habitats teeming with plant and animal life. Arising in the highlands upstate, they course across the Piedmont and Coastal Plains of Alabama and Mississippi merging with other streams and picking up strength on their way to the Gulf of Mexico. As they cut through the southern pinelands they heap up great piles of sugar-fine white sand forming sandbars at each meander in their snake-like journey. Trees leaning over the river are periodically dislodged by floods and fall into the river creating snags that are perfect for basking map turtles and their neighbors. Other turtle species that live in the rivers include softshell turtles (Apalone species), musk turtles (Sternotherus species), alligator snapping turtles (Macroclemys temminckii), slider turtles (Trachemys scripta), cooters (Pseudemys concinna), and in the case of the Pascagoula River, one other map turtle, Graptemys flavimaculata. The surrounding uplands support dwindling populations of gopher tortoises (Gopherus polyphemus) and the more plentiful, but still declining, box turtle (Terrapene carolina). |
| Collecting map turtles on these rivers is an experience few would forget. I remember one expedition to the Conecuh River in particular. I had invited my friends and colleagues Tony and Josh to help me collect the type specimens of G. ernsti. Any time a new species is described to science, the scientist who publishes the description must designate a specimen that is the reference for the species against which future comparisons can be made when necessary. These specimens are maintained in museums for other scientists to examine. Although collecting most turtle species is not difficult for trained ecologists, collecting turtles from big rivers has its own special challenges. |
|
To start with, G. ernsti are
almost impossible to catch by hand. They are very shy and submerge at the
first sign of trouble. In addition, big nets are difficult to use in the
powerful currents of these great rivers. After coming to these conclusions
my partners and I decided that the easiest way to catch large map turtles
would be to spot them while they were basking, and then we would dive into
the log jams when they submerged and search for them among the jumble.
Rivers with alligators and alligator snapping turtles add an extra element
of excitement to the experience. Also, big rivers are often heavy with
sediments picked up along the way, and underwater visibility is usually
poor. We needed a diving mask.  Diving for Graptemys |
At the time we were in southern Alabama, diving masks where not easy to find in small towns with even smaller stores. After much searching we finally found a store that sold a children’s beach set with a small mask and snorkel about the diameter of a drinking straw. Tony decided that he would be the diver. Back on the river it quickly became apparent that Tony’s adult-sized nose would have a difficult time fitting into the child-sized mask. By pushing his nose sideways he was finally able to fit the mask to his face for brief periods of time before the water came gushing in around the sides. In spite of the limitations of our equipment, Tony was able to catch the map turtles I needed. |
|
Unfortunately, these untamed southern rivers are no longer able to protect map turtles from the modern world. Collectors take untold numbers of attractive juveniles for sale in the national and international pet trade. Unsportsman-like fishermen shoot basking turtles for target practice when the fish aren’t biting and they are bored. We found carcasses of turtles with bullet holes in their shell along the Pascagoula River. Even the water itself can be unsafe with textile mills, pulp mills, and other industry polluting the rivers and jeopardizing the survival of all the aquatic species therein. Native mussel species on which female map turtles depend for food have been especially hard hit with many species facing extinction. Two map turtles, G. flavimaculata in the Pascagoula River and G. oculifera in the Pearl River are listed as threatened species under the United States Endangered Species Act. Many like the Escambia and Pascagoula map turtles are equally threatened, but without protection under the Endangered Species Act. While some species are adequately protected under state laws and regulations, others are not. |
|
Many of the map turtles are endemic to a particular river meaning that they are found nowhere else in the world. Thus, they are a treasured part of a state’s and Nation’s natural heritage. It is important for America to protect our biodiversity and map turtles are a part of that responsibility.
|
|
