Frequency of and Temporal Trends in Shell Anomalies in a Turtle Community in a Northern Indiana Lake

We used a 36-yr study of a turtle community in a northern Indiana lake to examine shell anomalies and temporal changes in their frequency in 3 species. The overall frequency of shell anomalies was 17% in painted turtles (Chrysemys picta), 11% in northern map turtles (Graptemys geographica), and 18% in red-eared sliders (Trachemys scripta elegans), and there were more anomalies on the carapace than on the plastron in 2 species (C. picta and G. geographica). The probability that an individual would have a shell anomaly was affected negatively by year of first capture and estimated year of hatching in C. picta and by carapace length at first capture in C. picta and T. s. elegans, although the relationships were weak (all r2 ≤ 0.15). Thus, there was no suggestion of a systematic change in shell anomalies over time in the Dewart Lake turtle community.