TPWD – Distribution, Occupancy, and Mercury Bioaccumulation of Alligator Snapping Turtles in Texas

Date: Wednesday, September 21, 2022
Time: 12:00 p.m. – 1:00 p.m.

Webinar Description: Eastern Texas contains the southwestern range edge of the alligator snapping turtle (Macrochelys temminckii). The state ranks the alligator snapping turtle as an S2 (imperiled) Species of Greatest Conservation Need, and has protected it as a threatened species since 1987. The species has a wide native range in 14 states of the southeastern United states, occurring in watersheds that drain into the Gulf of Mexico as far north as Illinois. Surveys in states at the range edge of the species, including Kansas and Oklahoma, suggest that its overall range may be contracting, providing an impetus to fully understand its distribution throughout Texas.

The species was historically commercially harvested in many parts of its range, particularly through the 1960s and 1970s. This may have contributed to skewed population demographics and population declines in harvested waters. Past commercial harvest, contemporary take (both legal and illegal), and habitat alteration are all inferred to imperil the persistence of the species.

For these reasons, the alligator snapping turtle has been petitioned for federal protection since 1982. In 2021, the United States Fish and Wildlife Service (FWS) compiled a Species Status Assessment (SSA) and proposed the turtle for listing as a threatened species under the Endangered Species Act. Relative to other states, data available on the species within Texas that the FWS had available to use in its SSA were limited. Particularly, information regarding large scale patterns in the distribution and demography of the species, and longitudinal data describing the dynamics of these parameters, were lacking.

In this study, we collected contemporary baseline occurrence data of the species throughout its putative range in eastern Texas to gain a more comprehensive understanding of its current distribution. Data from a previous distributional survey for the species in Texas completed in 2002 enabled us to assess whether changes in its distribution have occurred over the past two decades. We also examined the effects of environmental variables on both the detectability, occurrence, and abundance of the species. Sampling efforts provided us the opportunity to determine exposure of Texas alligator snapping turtles to mercury (Hg), a ubiquitous contaminant of aquatic systems. The predominately piscivorous diet and longevity of the species may predispose it to accumulate high levels of Hg, and analyzing concentrations allowed inference of potential health risks the contaminant poses to the species and people who legally and illegally harvest it for consumption.

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