False Map Turtle (Graptemys pseudogeographica) Distribution and Abundance in a Modified River Habitat in South Dakota

Anna Kase, University of South Dakota


Five turtle species are native to the South Dakota portion of the Missouri River: smooth softshell turtles (Apalone mutica), spiny softshell turtles (Apalone spinifera), painted turtles (Chrysemys picta), common snapping turtles (Chelydra serpentina), and the state threatened false map turtles (Graptemys pseudogeographica). While historically G. pseudogeographica were found in the northern stretches, damming of the river formed Lake Oahe where G. pseudogeographica are now seldom found. During 2017, 2018, and 2019 we conducted surveys along the northern and southern stretches of the river to estimate the distribution and abundance of these species. We performed visual surveys from boats driven along the shoreline, set baited hoop-net traps, and collected habitat data both during surveys and from satellite imagery. We detected all five species of turtles and found strong associations between different turtle species and specific habitat features. A. mutica and C. picta were associated with rock and gravel basking substrates found in the reservoir, and G. pseudogeographica with deadwood basking substrates found in riverine habitats. We found 0.21 deadwood basking sites per shoreline mile surveyed in Lake Oahe, compared to 5.0 deadwood basking sites/shoreline mile downstream of the Oahe Dam and 9.0 deadwood basking sites/shoreline mile in a more southern reach. The association of suitable basking habitat with G. pseudogeographica abundance suggests that the loss of this habitat feature may play an important role in their reduced distribution. Although removal of dams is unlikely, the implementation of woody debris might contribute to maintaining any small population still persisting in Lake Oahe.