Literaturdatenbank
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Bower, D. S. (2011). Conservation biology of freshwater turtles in the lower murray river of australia. Unpublished thesis , University of Canberra, anberra.
Added by: Admin (06 Jan 2014 18:22:40 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: anon2011b View all bibliographic details  |
Categories: General Keywords: Australien - Australia, Chelidae, Chelodina expansa, Chelodina longicollis, Emydura macquarii, Habitat - habitat, Schildkröten - turtles + tortoises Creators: Bower Publisher: University of Canberra (anberra) |
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| Abstract |
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Regulation of freshwater systems for human use has contributed to the degraded state of wetlands and rivers worldwide. Threats to freshwater biota are disproportionately higher than other ecosystems because freshwater systems have high biodiversity in a small area. In addition, the importance of freshwater to human food production and drinking water results in greater demands and pressures on these systems. When humans take control of functions that were previously climatic, such as hydrological regimes, an onus of responsibility to manage environmentally responsibly is acquired. Knowledge of the ecology and physiology of biota is necessary to determine the impacts of regulation on relevant populations and to predict responses of future management actions. The lower Murray River is the distal catchment in Australia’s most significant drainage basin, the Murray-Darling Basin. The basin became highly regulated following European settlement, which altered the functioning of the system. A primary threatening process within the system is the salinisation of land and waterways. Three freshwater turtles that vary in life-history strategies reside within the lower Murray catchment but their population performance and threatening processes are unknown. The first part of this thesis contains an ecological study to address the paucity of baseline information on freshwater turtles in the lower Murray River. Specifically, I aimed to (a) determine the distribution and density of freshwater turtles in the lower Murray River (b) determine the importance of habitat variables in freshwater turtle population performance, and (c) examine the home-range, seasonal movement and habitat use of the least known turtle species, Chelodina expansa. The second part of this thesis determined the physiological tolerance of freshwater turtles to salt exposure, in order to assess the potential of salinisation to threaten the persistence of turtle populations. Specifically, I aimed to (a) determine the tolerance of Chelodina expansa and Emydura macquarii to an increased ambient salinity, (b) examine the ionic response of wild turtle populations in saline environments to measure osmotic stress, and (c) determine the influence of salinity on embryonic development during incubation. Emydura macquarii, Chelodina expansa and Chelodina longicollis were present in every study site sampled between Wentworth and Murray Bridge. Detectability of species varied as a function of the trapping effort and depth within each transect and according to the study site. This highlighted the need to account for imperfect detectability when assessing changes in population size among sites or over time. Species assemblages and densities varied throughout the river but were dominated by Emydura macquarii in seven of the nine sites. In contrast with previous studies, density of Emydura macquarii was positively correlated with the distance to the river and water level fluctuation, a difference which may be explained by reduced environmental variation following prolonged drought. In contrast to previous belief, Chelodina expansa was abundant throughout the river system and the dominant species in the river between lock nine and ten. Female Chelodina expansa occupied discrete home ranges (1.43 ± 1.73 km) regardless of whether they were in the main channel or backwater, whereas male turtles occupied larger home ranges (7.9 ± 1.01 km) and regularly swam between backwater and river channel. Male turtles also made extensive upstream movements, up to 25 km. Individual male movements occupied up to 86% of the distance between weirs, suggesting that opportunities for movement may be reduced by aquatic barriers and these changes may influence turtle dispersal and behaviour. Large home ranges and use of both in-channel and off-channel waters, suggest that the impacts of management regimes that put aquatic barriers in place such as backwater disconnection and weirs, may influence turtle behaviour. Chelodina expansa and Emydura macquarii demonstrated remarkable tolerances to brackish water. During exposure to 15‰ saline water, Chelodina expansa and Emydura macquarii had increased sodium, chloride, urea and uric acid concentrations in the plasma, a mechanism to increase body osmolality and decrease water loss to the external media. Additionally, Chelodina expansa and Emydura macquarii behaviourally avoided salt intake by reducing food consumption in saline water. This suggested that behavioural constraints could limit the persistence of freshwater turtles in regions affected by salinisation. In wild populations exposed to prolonged periods of brackish water, Chelodina longicollis, Chelodina expansa and Emydura macquarii were not osmotically stressed. All species had higher concentrations of plasma sodium and chloride than those from freshwater but levels of urea or uric acid were not increased. In contrast, Chelodina longicollis from a highly saline site had increased levels of urea and uric acid, in addition to sodium and chloride, demonstrating that the physiological mechanism used to decrease the osmotic gradient was occurring in these populations. In addition, the carapace of these individuals was parasitised by a marine bristle worm. While short periods of high salinity are unlikely to adversely affect freshwater turtles through osmotic stress, the ability of turtles to persist in saline environments may be greatly influenced by ecological interactions. Chelodina expansa eggs incubated in higher salinities had higher mortality and smaller, lighter hatchlings with larger residual yolk sacs. Saline incubation media also increased concentrations of plasma -sodium, -chloride, -potassium, which suggests that embryos may not effectively regulate ionic concentrations. Effects of salinity mirror those caused by dry incubation media because both processes lower the water potential of the media. Salinisation of river banks has the potential to reduce hatching success and morphology of Chelodina expansa. These findings suggest salinisation may affect other nesting reptiles. Knowledge of freshwater turtle behaviour and life history can be used to predict the impact from water initiatives to inform management. Disconnecting backwaters is likely to provide a barrier to turtles, inhibiting aquatic movement. New knowledge of the large and frequently movements of male turtles in and out of backwaters suggested that backwater disconnections are likely to obstruct turtle behaviour. Secondly, blocking backwaters decreases water quality as evident by the corresponding increase in salinity. Turtles in brackish lakes were in the initial stage of osmotic stress, with no increase in urea or uric acid and still feeding. This suggested that low levels of salinity for short periods of time are unlikely to cause adverse impacts directly. Whilst the current study suggested that all three turtle species are widely distributed in the lower Murray River, the reliance of Emydura macquarii and Chelodina expansa on the river system leaves the persistence of these species dependant on the ability of the river to provide basic requirements for population function. Yet river health is declining. The continually degrading condition of the lower Murray River and its associated landscape is attributed to increased anthropogenic pressures and will shortly interact with climate change. Maintaining a healthy river is of paramount importance if this system is to continue supporting the species that we value.
Added by: Admin |