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Beerwah, Australia

Campbell H.A.,University of Queensland | Dwyer R.G.,University of Queensland | Irwin T.R.,Australia Zoo | Franklin C.E.,University of Queensland
PLoS ONE | Year: 2013

The estuarine crocodile (Crocodylus porosus) is the apex-predator in waterways and coastlines throughout south-east Asia and Australasia. C. porosus pose a potential risk to humans, and management strategies are implemented to control their movement and distribution. Here we used GPS-based telemetry to accurately record geographical location of adult C. porosus during the breeding and nesting season. The purpose of the study was to assess how C. porosus movement and distribution may be influenced by localised social conditions. During breeding, the females (2.92±0.013 metres total length (TL), mean ± S.E., n = 4) occupied an area<1 km length of river, but to nest they travelled up to 54 km away from the breeding area. All tagged male C. porosus sustained high rates of movement (6.49±0.9 km d-1; n = 8) during the breeding and nesting period. The orientation of the daily movements differed between individuals revealing two discontinuous behavioural strategies. Five tagged male C. porosus (4.17±0.14 m TL) exhibited a 'site-fidelic' strategy and moved within well-defined zones around the female home range areas. In contrast, three males (3.81±0.08 m TL) exhibited 'nomadic' behaviour where they travelled continually throughout hundreds of kilometres of waterway. We argue that the 'site-fidelic' males patrolled territories around the female home ranges to maximise reproductive success, whilst the 'nomadic' males were subordinate animals that were forced to range over a far greater area in search of unguarded females. We conclude that C. porosus are highly mobile animals existing within a complex social system, and mate/con-specific interactions are likely to have a profound effect upon population density and distribution, and an individual's travel potential. We recommend that impacts on socio-spatial behaviour are considered prior to the implementation of management interventions. © 2013 Campbell et al. Source

Campbell H.A.,University of Queensland | Watts M.E.,University of Queensland | Sullivan S.,Queensland Parks and Wildlife Service | Read M.A.,Queensland Parks and Wildlife Service | And 3 more authors.
Journal of Animal Ecology | Year: 2010

1. The estuarine crocodile (Crocodylus porosus) is the world's largest living reptile. It predominately inhabits freshwater and estuarine habitats, but widespread geographic distribution throughout oceanic islands of the South-east Pacific suggests that individuals undertake sizeable ocean voyages. 2. Here we show that adult C. porosus adopt behavioural strategies to utilise surface water currents during long-distance travel, enabling them to move quickly and efficiently over considerable distances. 3. We used acoustic telemetry to monitor crocodile movement throughout 63 km of river, and found that when individuals engaged in a long-distance, constant direction journey (>10 km day -1), they would only travel when current flow direction was favourable. Depth and temperature measurements from implanted transmitters showed that they remained at the water surface during travel but would dive to the river substratum or climb out on the river bank if current flow direction became unfavourable. 4. Satellite positional fixes from tagged crocodiles engaged in ocean travel were overlaid with residual surface current (RSC) estimates. The data showed a strong correlation existed between the bearing of the RSC and that of the travelling crocodile (r 2 = 0Æ92, P < 0Æ0001). 5. The study demonstrates that C. porosus dramatically increase their travel potential by riding surface currents, providing an effective dispersal strategy for this species. Source

Leblanc M.,IRD Montpellier | Leblanc M.,James Cook University | Leblanc M.,University of Avignon | Tweed S.,IRD Montpellier | And 8 more authors.
Journal of Hydrology | Year: 2015

One of the world's largest bauxite deposits is located in the Cape York Peninsula, North-East Australia. Little is known about the hydrology of these remote bauxite deposits. Here, we present results from a multidisciplinary study that used remote sensing, hydrochemistry, and hydrodynamics to analyse the occurrence of several large oases in connection with the bauxite plateaus. Across this vast region, otherwise dominated by savannah, these oases are sustained by permanent springs and support rich and diverse new sub-ecosystems (spring forests) of high cultural values to the local indigenous population. The spring water chemistry reveals a well-mixed system with minor inter-spring variation; TDS values of spring waters are low (27-72mgL-1), major ion compositions are homogenous (Na-Si-DIC-Cl) and δ18O and δ2H values are reflective of rainwater origin with little evaporation prior to recharge. Dating of spring waters with anthropogenic trace gases (CFC-12 and SF6) indicates mean groundwater residence times ranging from <1 to 30years. An artificial tracing experiment highlighted the existence of a flow pathway from the bauxite land surface to the sandy aquifer that feeds the springs through discontinuities in the ferricrete layer. In addition, the soil infiltrability tests showed the bauxite land surface has very high infiltrability (15mmmin-1), about four times greater than other adjacent land surfaces. Across the lower part of the Wenlock Basin, satellite data indicate a total number of 57 oases consistently located on the edge of the bauxite plateaus. This super-group of permanent hillslope springs and their ecosystems adds another important attribute to the list of natural and cultural values of the Cape York Peninsula. © 2015 Elsevier B.V. Source

Campbell H.A.,University of Queensland | Campbell H.A.,University of New England of Australia | Dwyer R.G.,University of Queensland | Wilson H.,University of Queensland | And 2 more authors.
Animal Conservation | Year: 2015

Preserving large carnivores that perceive humans as prey brings conservation values into direct conflict with human security. Informing when and where humans and large carnivores occupy the same space may reduce attack frequency and promote coexistence. Here, we demonstrate a methodology to better understand the spatiotemporal relationship between a population of large carnivores and humans. The carnivore of study was the estuarine crocodile Crocodylus porosus, a large semi-aquatic predator responsible for 705 recorded human attacks over the last 20 years. Crocodiles were captured every August over 3 years and individuals greater than 2.5m in length were implanted with an acoustic transmitter (n=84). The transmitter emitted a coded pulse detected when in proximity to underwater hydrophones deployed throughout the river. The telemetry data informed which previously captured crocodiles were present during subsequent trapping episodes and adult population size was estimated using a closed-population model. Over 3 years, 24 of the tagged crocodiles were detected 269 times moving through a shallow-water area where humans frequently entered the water. The tagged crocodile presence was extrapolated to the population level to provide a probability of adult crocodile presence across a range of temporal scales. The results showed that between September and December, the probability of crocodile presence within the human entry zone was 0.97±0.01 during darkness but decreased to 0.07±0.01 during daylight, except around periods of high tide when it increased to 0.71±0.02. Human visitors confined their activity to shallow water during daylight hours, but no consideration was given to the significant rise in crocodile presence with season and tide. The observed patterns in crocodile and human behaviour, around this shallow-water river crossing, exhibited parallels with historical incidences of crocodile attack. © 2015 The Zoological Society of London. Source

Dwyer R.G.,University of Queensland | Campbell H.A.,University of Queensland | Campbell H.A.,University of New England of Australia | Irwin T.R.,Australia Zoo | Franklin C.E.,University of Queensland
Marine and Freshwater Research | Year: 2015

Underwater passive acoustic (PA) telemetry is becoming the preferred technology for investigating animal movement in aquatic systems; however, much of the current statistical tools for telemetry data were established from global positioning system (GPS)-based data. To understand the appropriateness of these tools for PA telemetry, we dual-tagged free-ranging aquatic animals that exist at the air-water interface (Crocodylus porosus, n≤14). The location of each animal was simultaneously recorded over a 3-month period by fixed acoustic receivers and satellite positioning. Estimates of minimum travel distance and home range (HR) were then calculated from the PA and GPS datasets. The study revealed significant disparity between telemetry technologies in estimates of minimum travel distance and HR size. Of the five HR measures investigated, the linear distance measure produced the most comparable estimates of HR size and overlap. The kernel utilisation distribution with a reference smoothing parameter function and ad hoc function, however, produced comparable estimates when raw acoustic detections were grouped into periods when animals were within and between receiver detection fields. The study offers guidelines on how to improve the accuracy and precision of space-use estimates from PA telemetry, even in receiver arrangements with large areas of non-detection. © 2015 CSIRO. Source

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