Living conditions of freshwater turtles and aquatic organisms in ponds invaded by exotic fishes in northeastern Chiba Prefecture

Abstract

We surveyed the living condition of freshwater turtles and aquatic organisms with traps at eight ponds in the northeast region of Chiba Prefecture in the summer (Jul–Aug) and fall (Oct–Nov) of 2012. All ponds were invaded by exotic largemouth bass Micropterus salmoides and/or bluegill Lepomis macrochirus. Freshwater turtles were observed in five of six ponds with freshwater aquatic organisms (small fishes and/or crustacean), whereas no turtles were observed in two ponds with no aquatic organisms. Chinese pond turtles Mauremys reevesii were captured in both seasons. There was no significant correlation between the number of Chinese pond turtles captured and any environmental factors (water temperature, dissolved oxygen, pH, and electric conduct- ivity) in either season. The number of Chinese pond turtles captured positively correlated with the number of topmouth gudgeon Pseudorasbora parva and freshwater shrimps (Palaemonidae) in the summer, and the number of the Chinese pond turtles also positively correlated with the number of red swamp crayfish Procambarus clarkii in fall. The number of red-eared slider (Trachemys scripta elegans) captured also positively correlated with the number of freshwater shrimp in summer, suggesting that the two turtle species were competing for the same pray. Results of multiple regression analysis indicated that while aquatic macrophytes had positive effects on the number of small aquatic organisms observed, invasive largemouth bass had a negative effect on the organisms captured in the study. These findings suggesting negative impacts of invasive largemouth bass on a number of aquatic organisms which are potential pray for freshwater turtles in these pond ecosystems.