Asad, S., J. Sikui, B. Binjamin & M.-O. Rödel

Natural history of three freshwater turtle species within two logging reserves in Sabah, Malaysian Borneo. pp. 251-262.

Abstract. Asian freshwater turtles are severely threatened by overharvesting for local and international trade. Whilst some research exists on their occurrence in market places, basic studies on their natural history are scarce. Effective conservation action requires an understanding of both the threats to a species and its ecology. Our research aims to elucidate some basic aspects of the natural history of three freshwater turtle species: Notochelys platynota, Heosemys spinosa and Dogania subplana in Sabah, Malaysian Borneo. We collected opportunistic turtle data within two logging concessions from 2017 to 2019, and conducted dedicated turtle sampling via Visual Encounter Surveys (VES) along rivers in 2019. These data were used to determine population characteristics, habitat associations/separation, movements, recapture rates, breeding
behaviour, and parasitism. We obtained 157, 40 and 13 records of N. platynota, D. subplana and H. spinosa, respectively. Roughly equal adult/juvenile ratios were detected in two species, whereas adults predominated (2.6:1) in N. platynota. Both N. platynota and H. spinosa exhibited similar sex ratios, with significant sexual dimorphism (males larger than females) in N. platynota. Notochelys platynota and D. subplana were significantly associated with wider streams compared to H. spinosa, whilst D. subplana were significantly associated with higher relative siltation than N. platynota. Recapture rates of N. platynota were low (N = 12), with recaptured N. platynota movements ranging from 10–489 meters. High rates of parasitism by freshwater leeches (Placobdelloides siamensis) were identified in N. platynota (41% of VES detections, N = 50), whilst 30% of H. spinosa were infested with ticks (N = 3). The effects of high parasitism on N. platynota require further study, however we observed a large breeding population of N. platynota in the logging reserves examined. Habitat separation between these three species at fine spatial scales, via stream width and siltation, likely permits their co-occurrence along the same stream networks. We recommend the protection of heterogeneous stream networks to improve effective conservation measures for these species.

Key words. Testudines, Notochelys platynota, Heosemys spinosa, Dogania subplana, population dynamics, habitat separation, parasitism, recapture rates.