Distribution status for invasive alien freshwater turtles Trachemys scripta (Thunberg in Schoepff, 1792) on Jeju Island, Republic of Korea

Several alien species of freshwater turtles have been imported to the Republic of Korea from various countries, and then released to the wild by breeders and as a part of religious practices throughout Korea. Here, we evaluated the number of subspecies of the alien freshwater turtle Trachemys scripta in the wild on Jeju Island, Korea. We confirmed the presence of three alien subspecies of freshwater turtles with higher number and broader distribution compared to previous studies in 2007 and 2015. There were 134 adult and 48 juvenile Trachemys scripta elegans in 41 locations; nine adult Trachemys scripta scripta in seven locations; and two adult Trachemys scripta troostii in two locations. Illegal release by humans and potential reproduction in the wild probably contributed to the increase in their numbers. Early detection of invasive alien species is crucial for preventing their spread. Therefore, to minimize their negative impacts on the natural ecosystem of Jeju Island, we suggest the continuous monitoring of invasive freshwater turtles (including the evaluation of their survival, growth, and reproduction) and the strengthening of regulations to prevent continued releases to the wild.