Changes in Population Structure of the Freshwater Turtle Mauremys japonica Following the Invasion of Feral Raccoon Procyon lotor in the Southern Tip of the Boso Peninsula, Japan

Abstract

The raccoon (Procyon lotor) was introduced to Japan from North America, and has been implicated in the population declines or local extinctions of native freshwater turtles. We conducted a capture–recapture study of the Japanese pond turtle (Mauremys japonica) at two sites in the Boso Peninsula, Japan, to investigate the effects of P. lotor predation on the demography of native turtle populations, during the period from 2014 to 2017, shortly after an invasion of P. lotor. The study revealed a steady decline in turtle population size, along with changes in age structure, characterized by a skew toward older age classes. We also found a number of living individuals with amputated limbs, which we suspect to be evidence of P. lotor predation. Such injuries highlight the importance of the early detection of population declines and identification of related warning signals or demographic characteristics, which in turn will enable the timely implementation of appropriate conservation measures to prevent local extinctions of freshwater turtles.