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Experimental Tests for an Effective Barrier Design to Exclude Diamondback Terrapins (Malaclemys terrapin) from Roads
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2025-01-01
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Edition:Final Report (March 2023–January 2025)
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Abstract:The objective of this project was to conduct experimental testing on fence designs that are effective in preventing diamondback terrapins (Malaclemys terrapin) from entering roadways to prevent the species from being impacted by road mortality. The diamondback terrapin is listed as a State Species of Concern in the State of Georgia. They are the only native brackish-water dwelling turtle species along the eastern seaboard of the United States and are facing population declines as a result of human encroachment and habitat modification. Specifically, this species experiences widespread road impacts throughout their range around coastal transportation infrastructure. This conflict between wildlife and transportation infrastructure occurs most frequently with nesting females, a critical demographic to the long-term viability of populations. Therefore, our goal was to devise an affordable structural option to prevent terrapins from entering US-80 (the Tybee Island Causeway) that aligns with the Georgia Department of Transportation construction, maintenance, and driver safety protocols. Specifically, we determined the height and angle specifications for the exclusion fencing implementation by testing three reverse curb designs: 90º flat surface, 90º with a 3” lip, and 70º reverse angle. Each curb had 2’ sections of 4 different heights: 6”, 8”, 10”, and 12”.The most effective heights were 12”, successfully excluding 100% of animals attempting to climb the barrier for the 90-degree, 98% of animals for the 70-degree reverse angle & 100% for 90 degree with 3” lip. Next, the 10” height successfully excluded 96% of animals for the 90-degree, 100% for the 70-degree reverse angle, and 100% for the 90-degree with 3” lip. At the 8” height, 70% of animals were excluded from the 90-degree, 97% from the 70-degree reverse angle, and 96% from the 90-degree with 3” lip. Lastly at the shortest 6” curb, only 64% of animals were excluded from the 90-degree, 96% were excluded from the 70-degree reverse angle, and 87% were excluded from the 90-degree with 3” lip. Overall, the 10” and 12” heights of the 70-degree reverse angle curb and the 90-degree with 3” lip curb were most successful at excluding terrapins. This research can guide GDOT towards adapting a concept into an effective barrier design that will be permanent, reduce maintenance costs, and increase safety on US-80 and future causeway or coastal projects where impacts to terrapins need to be mitigated. These results have broader application to diamondback terrapins throughout their range and to other hard-shelled chelonids on a global scale.
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[PDF-3.86 MB]
