by Will Selman
The Pearl River system hosts two unique turtle species: the Ringed Sawback (Graptemys oculifera) and the Pearl Map Turtle (Graptemys pearlensis). Neither of these species can be found anywhere else in the world… only the Pearl River system of Mississippi and Louisiana! The Ringed Sawback was designated as federally threatened in 1986, while the Pearl Map Turtle was petitioned in 2011 to be listed under the Endangered Species Act. Both turtle species are of conservation concern for a number of reasons mainly associated with alterations to their river habitat. Alterations include construction of dams, channelization of rivers, and excess river sedimentation.
Millsaps College students and I have been conducting surveys for the Ringed Sawback and Pearl Map Turtle over the last couple of summers in the Jackson area. Our surveys are inclusive of the One Lake Project Area (i.e., where the lake will be constructed), and our surveys also include both upstream and downstream segments of the Project Area. The data we have collected over the last couple of summers are in contradiction to many of the statements recently published in the Integrated Draft Feasibility & Environmental Impact Statement (hereafter, draft EIS) by the Rankin-Hinds Pearl River Flood Drainage and Control District. Below I highlight a few of our findings and compare them to the draft EIS.
Finding 1: The draft EIS states that “survey efforts have been limited and the extent of the [Ringed Sawback] population within the Project Area is not known at this time.” Contrary to this statement, our surveys have found that the Ringed Sawback can occur in great numbers upstream, downstream, and within the Project Areato be impounded by One Lake. Based on our population surveys in this stretch, we have observed between 56 – 280 Ringed Sawbacks basking per river mile within the Project Area. When we survey, we only count turtles basking on logs, and this count is not inclusive of the many turtles that may be underwater and unobservable during our surveys. Therefore, if we account for those that are unobservable, we estimate that the total Ringed Sawback population in the Project Area is likely ~1,200 – 2,500 individuals (including adults and juveniles).
Finding 2: The draft EIS states that previous flood control projects in Jackson have “degraded habitat for Ringed Sawbacks and nesting habitat is almost non-existent.” Indeed, the channelization and desnagging of the Pearl River has negatively impacted portions of the riverine habitat in the Project Area (mostly between Lefleur’s Bluff State Park and south of I-20). But as mentioned above, our research indicates that a healthy Ringed Sawback population occurs where the One Lake Project is proposed. Further, a recently published study indicates that the population north of Lakeland Drive is the most stable of five sites studied for the last 30 years, and the Lakeland population has increased in size since 2000; three of the other four study populations were declining (Jones 2017).
Contrary to the draft EIS, we also have observed direct evidence of significant nesting and successful reproduction of Ringed Sawbacks in the Project Area. We have observed Ringed Sawback females nesting on sandbars in the Project area, seen many tracks on sandbars by nesting females, and nests destroyed by predators; all of these are indicative of suitable nesting habitat and a reproductively viable population. During a survey this year, we observed that 27% of the basking turtles were hatchlings or juveniles, and this is indicative of exceptional recruitment in this stretch over the last couple of years. It is unknown why reproduction has been so successful in this urban stretch of river, and it seems somewhat counterintuitive.
Finding 3: The draft EIS states that the impacts to the Ringed Sawback population will be “minor in intensity and long-term in duration.” For both turtle species that specialize in flowing Pearl River habitats, if a dam turns a flowing river into a stagnant lake, these riverine turtles will likely be lost over time. I would consider such a change “habitat alteration”, a primary threat to the species outlined in the U.S. Fish and Wildlife Ringed Sawback Recovery Plan. Impounding a river to form a lake is equivalent of taking a hardwood forest, cutting it down, and planting a row crop like corn; the habitat will be completely altered to something dissimilar to its current state. We have observed in Crystal Lake and Mayes Lakes (old channels of the Pearl that are now lakes) that there are only a few Ringed Sawbacks compared to turtles that prefer non-flowing water, like Red-eared Sliders. Similarly, if the One Lake Project is constructed, I suspect that some Ringed Sawbacks will likely “hold on” in the lake. But over time, common turtles that are better adapted to the non-flowing water will replace Ringed Sawbacks. Thus, turtles will still occur in the lake, but the rare species like the Ringed Sawback and Pearl Map Turtle will disappear over time, and the area will be colonized by cosmopolitan species. Therefore, I would suggest that the impacts to this population will not be “minor in intensity.” I suggest that it will be major in intensity and long-term in duration.
The draft EIS makes many assumptions about the Ringed Sawback, but it does not have any data to support these assumptions. However, our survey data indicates that Ringed Sawbacks can occur in great abundance along the Project Area and recruitment/reproduction are better in this stretch than what has been observed in most Ringed Sawback populations. Thus, if completed, the One Lake Project will be a major blow to this population and negatively impact the recovery of the species.
Will Selman is an assistant professor of Biology at Millsaps College in Jackson, MS. He has conducted population surveys and ecological research on Map Turtles and Sawbacks in Mississippi, Louisiana, and Alabama over the last 15 years.