Aspects of the Biology of the Flattened Musk Turtle, Sternotherus depressus in Northern Alabama
Authors: Dodd C. Kenneth , Enge Kevin M. , Stuart James N. 
Published: February 2024

The flattened musk turtle, Sternotherus depressus, is endemic to streams and rivers of the Warrior River Basin in northern Alabama. Threats of habitat alteration and commercial collecting led to its listing as a threatened species under U.S. federal law. The life history of the species is poorly known. From April through September 1985 we surveyed 1 km sections of 10 streams to determine life history information, population structure, and habitat use. We further evaluated the effects of habitat degradation on turtle populations as a result of coal mining. The results suggest that mining siltation has a negative impact on the distribution and population structure of the flattened musk turtle. Turtle populations in mine-impacted sites were small with population structures skewed toward old individuals compared with sites not impacted by mining. Only the population at Sipsey Fork, unaffected by mining, had a large population of S. depressus, but numbers and total biomass were less than literature reports for other kinosternid turtles. Another population unaffected by mining was small but showed good recruitment while two additional unaffected populations showed population structures reflecting commercial collecting. Except at Sipsey Fork (with approximately 600 flattened musk turtles), there were too few turtles with which to make reliable population estimates despite intensive sampling. The overall sex ratio was 15 males per female, but varied substantially between populations. The environmental variables correlated with viable turtle populations were low conductivity, a pH between 6.5 and 7.5, and an oxygen value > 7.0 ppm. Turtles avoided deep slow-moving pools, shallow sandy areas, and areas affording little cover. S. depressus remains in a small area most of the time, with occasional long distance movements of unknown purpose. Turtles moved from 0 m to 460 m overnight, with males moving more often and for longer distances than females. Neither local nor occasional long distance movements were influenced by weather variables. Individual turtles overlapped both in movement and cover site selection, and there was no evidence of competition for cover sites. We recorded 67 instances of basking. Basking platforms included branches, logs, rocks, a rock face, and land. Turtles selected sites over deeper ( > 450 mm) water. Turtles basked aerially in the direct sun and were alert, but many appeared sick. Cloacal temperatures were as high as 33.1°C. Power function exponents of regressions of weight on carapace length were near 3.0, as expected. Regressions of weight on carapace width, plastron length, and plastron width were also near 3.0 indicating similar growth relationships among these characters. Regressions of other morphological comparisons were often significant but explained only a small amount of variance. Past and present threats of habitat degradation from mining, agricultural and municipal sources, and impoundments have combined to isolate the remaining populations of this species. Habitat fragmentation may be the most serious threat to the long-term survival of the flattened musk turtle.