If you don’t pay close attention when passing portions of the Pascagoula River drainage, you may not realize that these turtles are often basking and floating just below. The Pascagoula Map Turtle may be one such turtle, found in flowing water in southeastern Mississippi. They live in rivers and larger streams that are part of the greater Pascagoula River watershed.
The Pascagoula Map Turtle is a big freshwater turtle native to Mississippi, and females are often multiple times larger than males. Pictured above is a younger male turtle, complete with the characteristic blue-green head coloration and yellow shell markings. I caught this little guy while snorkeling in this medium-bodied creek, classic habitat for the species found in specific watersheds in the southeastern United States. They are very shy (another reason why many have not taken a good look at them), so snorkeling and kayaking surveys are standard for scientists collecting information on them.
Compared to other species, this turtle is relatively new to human knowledge. It was first described in 1992 based on slight differences in their markings (Lovich and Ennen 2014). In 2010, a slew of similar species were described in distinct drainages along the Northern Gulf of Mexico based on genetics and endemism to river systems (Ennen et al. 2010). Despite their similarity in appearance, you tend to know which turtle of this group you’re looking at simply by checking your map.
Intense size differences between males and females is common in North American freshwater turtles. Map turtles are particularly extreme cases. G. gibbonsi is a member of the ‘megacephalic’ group of map turtles, meaning their heads grow to be really big. This phenomenon is only observed in females though. Females develop massive jaws for crunching on their primary food source: freshwater mussels (see below photos). Males retain proportional heads and eat soft-bodied invertebrates and small mollusks (Vučenović and Lindeman 2021).
When searching for Pascagoula Map Turtles, be sure to bring binoculars, and if you’re planning to photograph them a tripod helps. Like most map turtles, they enjoy basking on beached logs and branches (often at a ~ 45 degree angle!), but will readily plunge to the river below at the slightest disturbance. They have decent vision, so slow movements utilizing the cover of trees or the river bank are necessary to getting a good look at one. Keep an eye out for their brightly colored heads and shells from a distance and, in the case of females, big, thick jaws!
References
Ennen, J. R., J. E. Lovich, B. R. Kreiser, W. Selman, and C. P. Qualls. 2010. Genetic and Morphological Variation Between Populations of the Pascagoula Map Turtle (Graptemys gibbonsi) in the Pearl and Pascagoula Rivers with Description of a New Species. Chelonian Conservation and Biology 9:98–113.
Lovich, J. E., and J. R. Ennen. 2014. Graptemys gibbonsi. Catalogue of American Amphibians and Reptiles (CAAR).
Vučenović, J., and P. V. Lindeman. 2021. The Diets of the Pearl and Pascagoula Map Turtles (Graptemys pearlensis and Graptemys gibbonsi). Herpetologica 77.