Date of Graduation

12-2021

Document Type

Thesis

Degree Name

Master of Science in Biology (MS)

Degree Level

Graduate

Department

Biological Sciences

Advisor/Mentor

DeGregorio, Brett A.

Committee Member

Willson, John D.

Second Committee Member

Magoulick, Daniel D.

Third Committee Member

Middaugh, Christopher

Keywords

Arkansas; Harvest; Population; Turtles

Abstract

The United States is home to the second highest concentration of turtle species in the world, after Asia. As of 2018, there are 57 turtle species recognized within the US, 40% of which are listed as threatened or endangered, with the primary threats to population persistence identified as over-consumption and/or habitat loss. Within the US, the Mississippi Alluvial Valley (MAV) region represents the second highest turtle species richness, after the Mobile River Basin. The MAV region of Arkansas is one of the least regulated in terms of commercial aquatic turtle harvest and has undergone large-scale habitat conversion from bottomland hardwood forest wetlands to agriculture, yet little is known about freshwater turtle populations within this region. As awareness of the plight of turtles worldwide increases and studies continue to find current levels of commercial harvest unsustainable, biologists and conservation organizations have begun petitioning states to close or strictly regulate commercial turtle harvest. Baseline data on turtle populations in the MAV of Arkansas is lacking. We conducted a three-year capture-mark-recapture (CMR) study of turtle community composition, density, and demography in agricultural ditches and aquaculture ponds of eastern Arkansas, two abundant wetland habitats which are often targeted by commercial turtle harvesters. We captured and marked over 4,000 individual turtles of nine species including red-eared sliders (Trachemys scripta; N = 2695), spiny softshell turtles (Apalone spinifera; N = 640), common musk turtles (Sternotherus odoratus; N = 508), eastern mud turtles (Kinosternon subrubrum; N = 81), common snapping turtles (Chelydra serpentina; N = 56), river cooters (Pseudemys concinna; N = 11), southern painted turtles (Chrysemys dorsalis; N = 7), Mississippi map turtles (Graptemys pseudogeographica kohnii; N = 7), and alligator snapping turtles (Macrochelys temminckii; N = 2). We found that harvest severely reduces density of red-eared sliders and spiny softshell turtles in both pond and ditch systems for up to two years post-harvest and potentially causes shifts in community composition detectable for years after the initial removal event. We found no differences in turtle species richness or diversity between harvest status in ponds, but harvested ditches had higher mean Simpson’s diversity and species richness. There were relatively few consistent differences in density or demography within ditches, likely because the dynamic hydrology of ditches results in frequent immigration and emigration. Recently harvested aquaculture ponds had lower densities of red-eared sliders and spiny softshell turtles than unharvested ponds and were missing size cohorts, persisting for at least 5 years after harvest. Using supervised classification in a GIS, we delineated 22,317 ha of aquaculture ponds and more than 18,350 linear km of agricultural ditches occurring in the MAV. Based on our density calculations, we estimate that more than 2 million red-eared sliders and 427,000 spiny softshell turtles occur in ditches and aquaculture ponds of the region. Overall density of sliders was greater in ditches, with approximately 65% of our extrapolated abundance existing in this habitat type, while spiny softshell turtles are far more common in ponds, with only about 17% of our extrapolated abundance occurring in ditches across the MAV. Our density estimates were moderate compared to other reports in the literature. These turtles are clearly utilizing these habitats, sometimes occurring at high densities, yet they are not limitless. Harvest can reduce their populations and managers must take this into account.

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