Impacts of river alteration for flood control on freshwater turtle populations

The impacts of artificial river alteration for flood control on the dynamics of freshwater turtle populations were studied in small urban and rural river systems in northwestern Chiba Prefecture, Japan, from 2003 to 2006. The population density of the Reeve’s turtle, Chinemys reevesii, decreased markedly, from 279 turtles km⁻¹ in 2003 to 43 turtles km⁻¹ in 2006 in association with the artificial river alteration practices implemented by 2006. Low turtle population densities in other river sections where flood control measures have already been implemented suggest slow population recovery. River alteration practices also altered the age structures, sex ratios, and demographic characteristics of the turtle populations, although the exact consequences for population viability have not yet been determined. Because the turtles select concave submerged riverbanks or bottoms with slow or no current velocity, increased current velocity in the altered river section make the entire riverbank and bottom unsuitable for hibernation. Overall, river alteration for flood control during the winter season when turtles are inactive due to low water temperature negatively impacted freshwater turtle populations.