Academic literature on the topic 'Erosion – New South Wales – Macquarie Marshes'

The use of helicopters for the shooting of feral pigs in western New South Wales has become increasingly popular and widespread. Studies were conducted to evaluate the effectiveness of this practice in terms of population reduction, rate of population recovery and cost. The study site was an area of 120 km*2 on the southern edge of the Macquarie Marshes. Estimated population reductions, calculated by the index-removal method, over two consecutive years were 80 and 65%. The associated rate of increase (r) in the 12 months following the first population reduction was 1.34, which is equivalent to a recovery of 77% in numbers. Results and levels of control inputs were collated for an additional consecutive year and compared with other studies. Management implications from this study are also considered.

The Murray–Darling Basin is a Social-Ecological System (SES) of major importance to Australia and includes extensive wetland areas in the north-western parts of New South Wales. The Gwydir Wetlands and the Macquarie Marshes are the particular focus of this paper. These two wetland SES have undergone five successive adaptive cycles (phases) since they were first visited by Europeans in the early 19th century and the ecological, economic and social drivers initiating each transformation to a new cycle are described and analysed. The arrival of the European settlers with their domestic livestock rapidly displaced the Indigenous SES and the wetlands were extensively grazed; during wet periods the livestock were moved out of the wetlands and moved back in as the water receded. More recent land-use changes resulted from the building of major dams to enable storage of water for use in irrigated agriculture. A consequence of dam construction and water use has been a reduction in the frequency and extent of flooding, which has allowed many parts of the wetlands to be continually grazed. Furthermore, as machinery capable of cultivating the very heavy textured soils became available, dryland cropping became a major enterprise in areas of the floodplain where the likelihood of flooding was reduced. With the reduction in flooding, these wetland sites have been seriously degraded. The final phase has seen the invasion by an exotic weed, lippia [Phyla canescens (Kunth) Greene], which is a perennial that grows mat-like between other species of plants and spreads to produce a virtually mono-specific stand. The domestic livestock carrying capacity of the land becomes more or less zero and the conservation value of the wetlands is also dramatically decreased. Therefore, we suggest that lippia should be classed as an ecosystem engineer that has caused the latest transformation of these wetland SES and suggest research directions to investigate how they can be managed to revert to a state in which lippia is no longer dominant.

An exercise was conducted to evaluate the effectiveness of plans to eradicate feral pigs in an exotic disease emergency. The study site was an area of 120 km2 on the southern edge of the Macquarie Marshes in western New South Wales. Shooting from a helicopter accounted for 946 pigs at a rate of 39.2 per hour. This was at an average of 1.65 shots and a cost of $11.77 per pig. A further 43 were shot from the ground or trapped. Of an estimated initial population of 1238, 80% was removed. Telemetry studies conducted in conjunction with the exercise indicated that some pigs became attuned to the significance of a hovering helicopter and modified their behaviour to avoid detection. Movements also emphasised the need to match the boundaries of feral pig eradication zones with natural boundaries, where overlapping home ranges are minimal and densities low. Eradication of feral pigs during an outbreak of exotic disease may be an unrealistic goal, and it may be more efficient to aim to eradicate the disease within the feral pig population. This would be achieved by isolating those pigs carrying the infection; it does not necessarily require the removal of all feral pigs.

The offshore Sydney Basin is unique frontier acreage because it is adjacent to Australia's largest gas and petroleum market on the east coast of New South Wales. Although the onshore Sydney Basin has been tested by more than 100 petroleum exploration wells, no wells have been drilled offshore.New South Wales Permit NSW/P10 has an area of 9419 km2 and extends over the offshore northern and central Sydney Basin which contains Upper Carboniferous to Middle Triassic lithiclastic and siliciclastic sedimentary rocks and volcanics. Maximum depth to magnetic basement in NSW/P10 is greater that 9 km in the southern Macquarie Syncline and south of the New England Fold Belt at the continental margin. Recent seismic reprocessing and aeromagnetic surveying have focused the exploration effort on northern NSW/P10 where thick (greater than 1600 m) Upper Permian section containing source and reservoir facies is predicted. Other areas in the permit are less prospective because of widespread intrasedimentary magnetic bodies or the absence by erosion of Upper Permian and Triassic section.The Sydney Basin is an exhumed basin that reached its maximum depth of burial in the Early Cretaceous prior to basinwide uplift of 1.5-3.5 km during the Tasman Sea rifting. The magnitude and timing of the exhumation can be demonstrated with fluid inclusion, magnetisation, fission track and vitrinite reflectance data. The presence of commercial quantities of oil or gas in Upper Permian reservoirs depends on trap integrity having been maintained during the epeirogeny, or the re-migration of hydrocarbon into new traps.

Context Feral pigs (Sus scrofa) are a destructive invasive species that cause damage to ecologically sensitive areas. Management of biodiversity and of feral pigs assumes the diet of pigs of different ages and sexes are similar. Aims We aimed to investigate effects of feral pig age and sex on broad feral pig diet to identify potential at-risk native wildlife species so as to improve biodiversity and feral pig management. Methods Diet was determined by macroscopic analysis of the stomach content of 58 aerially shot feral pigs of mixed ages and sexes. The study occurred in the Macquarie Marshes, New South Wales, a Ramsar wetland of international significance. Results Feral pigs were largely herbivorous, with vegetable matter being found in all stomachs and contributing to a majority of the food material that was present in each stomach, by volume. Adult feral pigs had significantly more grasses and crop material in their stomachs than juveniles, while juveniles had significantly more forbs in their stomachs than adult feral pigs. Vertebrate prey items included frogs, lizard and snake, but no threatened wildlife species. Conclusions Juvenile and adult feral pigs differed in their diet, especially with regards to plant material, which has not been reported previously. There was, however, no difference in the consumption of vertebrate wildlife species between juvenile and adult, or male and female feral pigs. Slow-moving, nocturnal amphibians and reptiles were the most common vertebrate item recorded. Implications Biodiversity and feral pig management should recognise plant diet differences between demographic segments of the feral pig population. Further research is recommended to determine if diet differences also occur for threatened wildlife species, which will require more intensive nocturnal sampling.

Because it achieves rapid reductions in pig density, helicopter shooting is perceived to be a cost-effective option for feral pig control. In order to evaluate the cost effectiveness of the technique and develop predictive models of variation in costs, functional response models derived from predator–prey theory were fitted to 3 data-sets describing variation in kill rates with feral pig density. The data-sets were collected during shooting programs conducted on the Mary River floodplain in northern Australia, and on the Macquarie Marshes and Paroo River floodplain in western New South Wales. Fitted models indicated that variation in kill rates with pig density took the form of a Type 3 functional response for all 3 data sets, kill rates approaching a constant maximum at high pig densities and declining toward 0 at pig densities greater than 0. While maximum kill rates were similar for the 3 shooting programs (average 60.49 kill h–1, range 49.64–76.28), densities below which no pigs would theoretically be killed varied significantly (average 2.79 pigs km–2, range 1.34–5.02). Similar maximum kill rates for the 3 shooting programs indicates that, once located, the time taken by shooting teams to dispatch pigs was relatively constant (0.023 h). Variation in threshold densities below which no more pigs would theoretically be shot, indicates that as the density of pigs was reduced, their vulnerability to shooting teams differed between the 3 shooting programs. This may have reflected differences between sites in either the capacity of resident pigs to learn to evade shooting teams or, more likely, the availability of refuge habitat. For 2 of the shooting programs, too few data were available to estimate the effect of declining pig density on kill rate, precluding detailed examination of differences in the efficiency with which pigs were found (search efficiency). Using estimates of pig density below which no pigs would theoretically be shot to set a limit to the effectiveness of shooting programs, models predicting variation in hours per kill with pig density were derived from each data set. These models demonstrated that hours per kill increased exponentially as shooting reduced pig populations below threshold densities of approximately 2–6 pigs km–2. Generalised models relating variation in cost per kill to pig density for the 3 shooting programs are described.