Effects of Channelization on Sabine Map Turtle Habitat in the Mermentau River Drainage, Louisiana: Use of Original vs. New Channels

Abstract

Graptemys sabinensis (Sabine Map Turtle) occurs in the Sabine, Calcasieu, and Mermentau river drainages of Louisiana and Texas. The Mermentau River was altered by construction of seven cut-offs between the towns of Mermentau and Lake Arthur, LA, in the 1970s, and several cut-offs also have been constructed along the river's largest tributary, Bayou Plaquemine Brule. We surveyed basking turtles on lower Plaquemine Brule and the Mermentau River to determine if the new channels are used to the same extent as the original channels. The original channels had nonsignificantly higher counts of basking Sabine Map Turtles and total turtles than the new channels. However, the shorter new channels had significantly higher densities of Sabine Map Turtles and total turtles than the original channels. The new channels create a bypass for excess water on the river following heavy rainfall, allowing higher flow on new channels, which may be preferred by Sabine Map Turtles. There was no significant difference in Sabine Map Turtle density between the inner and outer banks of the Mermentau's original channels, presumably because dredging made the depths along the inner and outer banks similar; new channels also divert water away from the original channels during high-flow events, which may maintain the anthropogenically homogenized condition of the original channels.