Universiẗat, Diss., 2007--Giessen.

(1) Aerial survey methods for estimating population size of feral water buffalo in northern Australia were examined. (2) Line transect models underestimated population size. Of six models tested the most accurate underestimated by nearly half. The models give biased estimates most probably because not all animals on the survey line were sighted . (3) Aerial strip transect surveys were also negatively biased. The extent of this bias was estimated in index-removal experiments. Experiments were carried out on two populations in areas of differing obstructive canopy cover. (4) In woodland habitat with a canopy cover of 30- 60%, a correction factor of 3.2 was required to take account of animals not seen. In forest habitat with a canopy cover of 60-100%, a correction factor of 4.9 was required. (5) Using these results, the population size of feral buffalo, cattle and horses in Kakadu National Park was estimated by aerial survey at the end of each year over 6 years. Annual rates of increase for three regions of the Park were estimated, taking into account known removals from the population. The effects of dry season rainfall and population density in the preceding year on rate of increase were examined for each species. (6) The mean annual exponential rate of increase for each species was 0.10 yr-1 for buffalo, 0.23 yr-1 for cattle and -0.14 yr-1 for horses. (7) The annual rates of increase varied greatly between years within all species and were highly correlated with dry season rainfall in the year of survey for buffalo and cattle but not for horses. (8) No significant effect of preceding density on rate of increase was found for any species. A large reduction in buffalo populations did not correspond with an increase in unharvested populations of horses, suggesting the two species do not compete for food or other resources. (9) A campaign to control populations of feral water buffalo in Kakadu National Park was assessed. Between 1979 and 1988, approximately 79,000 animals were removed, 54% by commercial live-capture, 35% by shooting from helicopters and 10% by shooting from the ground. (10) In the period 1983-1988 when population estimates from aerial survey are available, mean buffalo population density was reduced from 5.60 km-2 to 1.17 km-2 over the surveyed area of the Park. (11) The costs of removal by shooting from helicopters, capturing animals alive and shooting from the ground were compared. The mean costs per animal in 1988 were $24.13, $74.53, and $86.02 respectively. (12) The effects of initial density and time spent shooting on number of animals removed by shooting from helicopters were examined. One linear and two curvilinear models were fitted to data from four different removal exercises. The relationship between time spent shooting and number removed was best described by a curvilinear (Ivlev) function. This model was used to estimate costs of control to a specified density. (13) Model regression coefficients differed between removal exercises, suggesting that the number removed may be affected by variables other than time spent shooting and initial density. Data from the range of conditions encountered during removal is thus likely to be required for robust estimation of removal costs.

The magpie goose (Anseranas semipalmata) is a spectacular and unique waterbird from tropical north Australia and southern New Guinea. Due to recent human persecution, the species has been eliminated from most of its former strongholds in southern and south-eastern Australia – reduced to small conservation-dependent populations through habitat loss, exploitation and drought. Yet, genuine conservation opportunity still exists in northern Australia, in the country's Northern Territory in particular, to maintain viable populations through evidence-based management of wetlands that support the waterbirds and mitigation of the threats posed by global change. Much has been achieved over the last 50 years to understand the ecology and life history of magpie geese, but little has been done to understand important population-level interactions with wetland habitat and the likely outcomes under climate warming, wetland loss to sea level rise, altered competitive interactions among wetland plants, increased frequency and severity of epizootics, and synergies with over-hunting. My review of pathogens and parasites likely to cause morbidity and mass mortality in magpie geese shows that bacterial diseases such as avian cholera and botulism, as well as pathogenic avian influenza viruses, pose the most serious threats. Bacterial diseases in particular are more likely to occur under warmer and wetter conditions, and geese are susceptible to these given large aggregations at favoured nesting and feeding sites. I use a metapopulation model to demonstrate that increased frequency and severity of epizootics will likely force extirpation of geese under current harvest rates across the Northern Territory. Magpie geese are also vulnerable to climate change through dependency on a favoured food plant – the water chestnut (Eleocharis dulcis). As a result of a two-year field programme, I was able to show how birds seasonally migrate and aggregate in response to the availability of this resource and gain body condition following predation on the root tubers of the plants. My geospatial modelling of ocean level inundation of wetlands that support E. dulcis show marginal habitat loss under 1.4 m of sea level rise, and large-scale losses under multi-metre sea level rise, but the current resolution of GIS data do not account for fine-scale saline water intrusion through channel or eroded levees. The population models constructed predict that magpie geese are broadly resilient to change where harvest is tightly regulated, but current harvest rates are unlikely to be sustainable. Given the importance of maintaining viable, connected subpopulations large enough to maintain genetic diversity, and because of the value of magpie geese to Aboriginal Australians as a food source, ongoing monitoring of geese population trends will be essential. Wetland management options include erecting buffers to stop or slow down saltwater intrusion resulting from sea level rise, and implementing a system to monitor annual indigenous harvest. Temporary restrictions on harvest may be necessary following mass mortality events such as epizootics or droughts. Only the careful management of wetlands that support current geese populations, and close monitoring of populations will ensure continued sustainable harvest of geese under global change. Given the cultural and biological significance of this species and the north Australian wetlands that support it, this is a conservation resource we cannot afford to squander. / Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Science, 2009

This thesis provides the measurements of 222Rn exhalation rates, 210Pb deposition rates and excess 210Pb inventories for locations in and around Ranger Uranium Mine and Jabiru located within Kakadu National Park, Australia. Radon-222 is part of the natural 238U series decay chain and the only gas to be found in the series under normal conditions. Part of the natural redistribution of 222Rn in the environment is a portion exhales from the ground and disperses into the atmosphere. Here it decays via a series of short-lived progeny, that attach themselves to aerosol particles, to the long lived isotope 210Pb (T1/2 = 22.3 y). Attached and unattached 210Pb is removed from the atmosphere through wet and dry deposition and deposited on the surface of the earth, the fraction deposited on soils is gradually transported through the soil and can create a depth profile of 210Pb. Here it decays to the stable isotope 206Pb completing the 238U series. Measurements of 222Rn exhalation rates and 210Pb deposition rates were performed over complete seasonal cycles, August 2002 - July 2003 and May 2003 - May 2004 respectively. The area is categorised as wet and dry tropics and it experiences two distinct seasonal patterns, a dry season (May-October) with little or no precipitation events and a wet season (December-March) with almost daily precipitation and monsoonal troughs. November and April are regarded as transitional months. As the natural processes of 222Rn exhalation and 210Pb deposition are heavily influenced by soil moisture and precipitation respectively, seasonal variations in the exhalation and deposition rates were expected. It was observed that 222Rn exhalation rates decreased throughout the wet season when the increase in soil moisture retarded exhalation. Lead-210 deposition peaked throughout the wet season as precipitation is the major scavenging process of this isotope from the atmosphere. Radon-222 is influenced by other parameters such as 226Ra activity concentration and distribution, soil porosity and grain size. With the removal of the influence of soil moisture during the dry season it was possible to examine the effect of these other variables in a more comprehensive manner. This resulted in categorisation of geomorphic landscapes from which the 222Rn exhalation rate to 226Ra activity concentration ratios were similar during the dry season. These results can be extended to estimate dry season 222Rn exhalation rates from tropical locations from a measurement of 226Ra activity concentration. Through modelling the 210Pb budget on local and regional scales it was observed that there is a net loss of 210Pb from the region, the majority of which occurs during the dry season. This has been attributed to the fact that 210Pb attached to aerosols is transported great distance with the prevailing trade winds created by a Hadley Circulation cell predominant during the dry season (winter) months. By including the influence of factors such as water inundation and natural 210Pb redistribution in the soil wet season budgeting of 210Pb on local and regional scales gave very good results.