Long-term Changes in Age Structures of a Naturalized Population of Freshwater Turtle, Red-eared Slider Trachemys scripta elegans

抄録

The red-eared slider turtle, Trachemys scripta elegans, is an invasive species, that may potentially induce negative impacts on native turtle communities and freshwater ecosystems. Effective control of invasive species requires knowledge of the process of invasion and the long-term dynamics of an introduced population. However, such studies are scarce. We investigated temporal changes in the species composition of a freshwater turtle assemblage including density and age structure of the red-eared slider turtle at the Kahokugata lagoon of Ishikawa Prefecture in central Japan over 15 years (2001–2003, 2013 and 2015). The number of red-eared sliders increased over time, whereas that of Reeves’ pond turtle, Mauremys reevesii, remained flat for 15 years from 2001 to 2015. Data on morphological measurements in the red-eared slider population showed that the proportion of old individuals increased whereas juveniles decreased. Moreover, the body condition index decreased in all age classes. These results suggest that juvenile recruitment was limited in the recent years and thus breeding efficiency was lowered in the red-eared slider population at this lagoon perhaps due to high population density.