Simple fence modification increases floodplain land movement prospects for freshwater turtles

Waltham, N.; Schaffer, J.; Perry, J.; Walker, S.; Nordberg, E.

doi:10.1101/2020.12.03.409607

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bioRxiv · 10.1101/2020.12.03.409607

Simple fence modification increases floodplain land movement prospects for freshwater turtles

Waltham, N.·Schaffer, J.·Perry, J.·Walker, S.·Nordberg, E.

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Abstract

Feral pigs predate on freshwater turtles and damage wetland habitats in the process. Installing fences successfully averts access and damage, however, they become a barrier for freshwater turtles requiring land access during migration. We collected 161 turtles (Chelodina rugosa, Emydura subglobosa worrelli, Myuchelys latisternum) from twenty floodplain and riverine wetlands during post-wet (June-August) and late-dry season (November-December) surveys (2015-2018) in northern Australia. Wetlands were either fenced (150 x 150mm square, 1.05m high wire mesh) or not around the wet perimeter. Nine-seven percent of individuals caught in either fenced or unfenced wetlands had a shell carapace width greater than mesh width, of these 44 (46%) were captured inside fenced wetlands, while 50 were caught in unfenced wetlands. The remaining 35 were smaller than 150mm and would easily pass through fence mesh. Sixty-five turtles partook in a fencing manipulative experiment. Turtles with carapace widths wider than mesh often successfully escaped through fences by lifting one side of their shell and passing diagonally. In a second experiment where a piece of vertical wire (1500mmx300mm) was removed, turtles located gates after prospecting and trying to fit through meshing areas that were too small to pass through. Nine-two percent of turtles were able to locate and pass through gates, while 8% failed to locate a gate after 2 hours. Three turtles that did not use gates, and seemed to give up and dug into the grass. Gates applied every 4m showed an 83% passage rate, every 2m was 91%, and while every 1m was 100%. Combing field and manipulative experiments revealed that large turtles will prospect and move along a fence until they find suitable passage. Applying turtle gates every 1-4m allows almost 100% passage, and if strategically applied in travel corridors, would minimize the need for large-scale clipping efforts around entire wetlands.

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Waltham, N., Schaffer, J., Perry, J., Walker, S., Nordberg, E.. 2020-12-03. Simple fence modification increases floodplain land movement prospects for freshwater turtles. https://doi.org/10.1101/2020.12.03.409607

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