Distribution and Abundance of Graptemys Species (G. nigrinoda and G. pulchra) in the Tombigbee River System of Northeastern Mississippi

Will Selman*

*Biology Department, Millsaps College, 1701 N. State Street, Jackson, MS 39201.

Southeastern Naturalist, Volume 23, Issue 4 (2024): 448–473

First published early online: 18 December 2024

Abstract
The river turtles Graptemys nigrinoda (Black-knobbed Sawback) and G. pulchra (Alabama Map Turtle) are endemic to the Mobile River drainage of Alabama, northwestern Georgia, and northeastern Mississippi. Little is known of their current distribution and abundance in the Tombigbee River (TR) system in northeastern Mississippi even though both are being considered for protection under the US Endangered Species Act. During May–July 2019, 2022, and 2023, I used a combination of methods (e.g., point-count surveys, basking-density surveys, trapping, mark–resight population estimates) to determine the presence and densities of both species in the TR drainage of northeastern Mississippi. Both Graptemys species were detected throughout most of the TR and Tennessee–Tombigbee Waterway (TTW). Black-knobbed Sawbacks and Alabama Map Turtles were both found in 5 previously undocumented creeks, and both species were found near or upstream of almost all historic localities. Basking densities at 33 sites were 15× greater for Black-knobbed Sawbacks (15.0 individuals/rkm) compared to Alabama Map Turtles (1.0 individuals/ rkm), while different habitat types had different densities of Black-knobbed Sawbacks and Alabama Map Turtles; both species occurred at their lowest densities in the TTW lakes. Trapping at 5 sites yielded 107 Black-knobbed Sawbacks and 14 Alabama Map Turtles, and mean mark–resight population estimates were 173 individuals/rkm (min–max: 82–397 individuals/rkm) at 5 sites for Black-knobbed Sawbacks and 13 individuals/rkm (4–20 individuals/rkm) at 3 sites for Alabama Map Turtles. Alabama Map Turtles are of greater conservation concern in Mississippi compared to Black-knobbed Sawbacks due to lower densities and apparent extirpation from parts of the drainage.

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