Jennifer Spencer

Response of estuarine wetlands to reinstatement of tidal flows

The importance of estuarine wetlands to ecosystem services such as primary productivity and flood attenuation, as well as their function as habitat for threatened species has prompted efforts to restore tidal flows to degraded wetlands. We tracked the response of estuarine vegetation to tidal-flow reinstatement over 12 years (1995–2007) in a wetland of the Hunter estuary, Australia. This site provides important habitat for migratory shorebird species, which favour shallow tidal pools and saltmarsh over mangrove forest. Increased tidal flows following culvert removal reduced shorebird roost habitat by 17% because of mangrove encroachment on saltmarsh and shallow tidal pools. Saltmarsh occurred in areas with a spring tidal range 0.4 above the Australian height datum (mAHD), whereas mangrove occupied areas with spring tidal range >0.3 m, hydroperiod <0.45 and elevation <0.4 mAHD. By using these parameters, it is possible to exclude mangrove from saltmarsh areas and to establish saltmarsh at lower elevations in the tidal frame than would occur under natural conditions, effectively expanding saltmarsh area. These measures can be useful where landward migration of estuarine communities is restricted by infrastructure; however, they should not be considered a substitute for conservation of remnant saltmarsh or establishment of landward buffer zones.

Identifying Critical Habitat for Australian Freshwater Turtles in a Large Regulated Floodplain: Implications for Environmental Water Management

Freshwater turtles face many threats, including habitat loss and river regulation reducing occupancy and contributing to population decline. Limited knowledge of hydrological conditions required to maintain viable turtle populations in large floodplain wetlands hinders effective adaptive management of environmental water in regulated rivers. We surveyed three turtle species over 4 years across the Lower Murrumbidgee River floodplain, a large wetland complex with a long history of water resource development. Using site and floodplain metrics and generalized linear models, within a Bayesian Model Averaging framework, we quantified the main drivers affecting turtle abundance. We also used a hierarchical modeling approach, requiring large sample sizes, quantifying possible environmental effects while accounting for detection probabilities of the eastern long-necked turtle (Chelodina longicollis). The three species varied in their responses to hydrological conditions and connectivity to the main river channel. Broad-shelled turtles (Chelodina expansa) and Macquarie River turtles (Emydura macquarii macquarii) had restricted distributions, centered on frequently inundated wetlands close to the river, whereas the eastern long-necked turtles were more widely distributed, indicating an ability to exploit variable habitats. We conclude that turtle communities would benefit from long-term management strategies that maintain a spatiotemporal mosaic of hydrological conditions. More specifically, we identified characteristics of refuge habitats and stress the importance of maintaining their integrity during dry periods. Neighboring habitats can be targeted during increased water availability years to enhance feeding and dispersal opportunities for freshwater turtles.

The effect of survey method on the detection probabilities of frogs and tadpoles in large wetland complexes

Knowledge of the probability of detecting a species with a given survey effort is important when planning monitoring programs. The present paper compares detection probabilities for six survey methods: audio-visual transect surveys targeting adult frogs, and sweep netting, bait traps, small fyke nets, large fyke nets and seine netting targeting tadpoles. Data were drawn from repeat surveys of 16 wetlands over a 3-year period (2008–2011). Detection probabilities of each method and species combination were determined by maximum likelihood estimation. Audio-visual surveys targeting adults had a higher probability of detecting individual species than did methods targeting their tadpoles. However, the presence of adults was a reasonably poor indicator of the presence of their tadpoles on any given survey occasion. Of the methods employed to target tadpoles, large and small fyke nets had a significantly higher probability of detecting tadpoles of all species than did bait traps, seining or sweep nets. Differences in the detection probability of different methods demonstrated that the choice of survey method can bias towards particular groups of species and, in some cases, underestimate breeding activity by frog species in large waterbodies.