Integrating telemetry with a predictive model to assess habitat preferences and juvenile survival in an endangered freshwater turtle

Abstract

1. The introduction of predators and habitat destruction is leading to a worldwide decline in freshwater turtles. Here, we assessed the preferred habitat and the predation rates for juveniles of the endangered Mary River turtle ('Elusor macrurus'). Juvenile turtles were fitted with miniaturised transmitters and located accurately over a 21-day period. Water depth and velocity were measured at each locality, and the data used to populate a predictive distribution model (ecological niche factor analysis - ENFA - with Mahalanobis distances). The model showed that the juvenile turtles preferred areas of shallow, slow-flowing water near riffles. Extrapolation of the model throughout the entire river trunk identified a further 49 discrete locations that possessed the environmental characteristics preferred by the juvenile turtles. A further 12 juveniles were released with long-life (9 months) acoustic transmitters, and static underwater receivers were deployed to continuously record the presence and absence of turtles. The passive telemetry results supported the ENFA model and also suggested a 50% predation rate of the juvenile turtles over 9 months. Half of the predated turtles were probably taken by fish, whilst the other half were taken by a bird or mammal predator (inferred by changes in the movement of the attached transmitters). Combining telemetry with a predictive distribution model showed where juvenile 'E. macrurus' are likely to be found and the riverine features that require preservation to conserve the species.