Kakadu National Park Research Articles

Spatial Dynamics of Invasive Para Grass on a Monsoonal Floodplain, Kakadu National Park, Northern Australia

African para grass (Urochloa mutica) is an invasive weed that has become prevalent across many important freshwater wetlands of the world. In northern Australia, including the World Heritage landscape of Kakadu National Park (KNP), its dense cover can displace ecologically, genetically and culturally significant species, such as the Australian native rice (Oryza spp.). In regions under management for biodiversity conservation para grass is often beyond eradication. However, its targeted control is also necessary to manage and preserve site-specific wetland values. This requires an understanding of para grass spread-patterns and its potential impacts on valuable native vegetation. We apply a multi-scale approach to examine the spatial dynamics and impact of para grass cover across a 181 km2 floodplain of KNP. First, we measure the overall displacement of different native vegetation communities across the floodplain from 1986 to 2006. Using high spatial resolution satellite imagery in conjunction with historical aerial-photo mapping, we then measure finer-scale, inter-annual, changes between successive dry seasons from 1990 to 2010 (for a 48 km2 focus area); Para grass presence-absence maps from satellite imagery (2002 to 2010) were produced with an object-based machine-learning approach (stochastic gradient boosting). Changes, over time, in mapped para grass areas were then related to maps of depth-habitat and inter-annual fire histories. Para grass invasion and establishment patterns varied greatly in time and space. Wild rice communities were the most frequently invaded, but the establishment and persistence of para grass fluctuated greatly between years, even within previously invaded communities. However, these different patterns were also shown to vary with different depth-habitat and recent fire history. These dynamics have not been previously documented and this understanding presents opportunities for intensive para grass management in areas of high conservation value, such as those occupied by wild rice.

Assessing the distribution and drivers of mangrove dieback in Kakadu National Park, northern Australia

Satellite observations of Australia's Gulf of Carpentaria between 1987 and 2015 highlighted that many mangroves on the coastline bounding low-lying plains were progressively extending inland and to a lesser extent, in a seaward direction. However, in 2015/16, a significant and widely publicised mangrove dieback event occurred, this was attributed to a combination of climate (temperature, precipitation anomalies) and a ~20–30 cm decline in sea level. A similar but unreported event also occurred in Kakadu National Park (NP) in the Northern Territory. This study aimed to a) quantify the extent of this dieback in the NP, b) establish the characteristics of mangroves (floristics, structure) and the substrate elevation prior to and following event and c) establish links with climate and sea level. Using time-series of high resolution airborne and Unmanned Airborne Vehicle (UAV) data, the majority of mangroves experiencing full or partial dieback were found to occur on the landward margins. Reference to sea-level data indicated that mangroves had colonised and retreated in unison with sea level fluctuations over previous decades but increased in overall extent and cover as sea level rise dominated. Mangroves experiencing full mortality were located on higher elevation substrates where the sea level/tidal influence was least. The study concluded that whilst short-term ENSO-related sea level may result in dieback in northern Australia, the long-term projection of an increase in sea level is anticipated to lead to extension of mangroves in the landward direction.

Incursion of the bivalve Potamocorbula faba into northern Australia: a record from a Holocene archaeological site in Kakadu National Park

Incursion of the bivalve Potamocorbula faba into northern Australia: a record from a Holocene archaeological site in Kakadu National Park

Savanna canopy trees under fire: long‐term persistence and transient dynamics from a stage‐based matrix population model

AbstractFire is a major disturbance driving the dynamics of the world's savannas. Almost all fires are set by humans who are increasingly altering fire timing and frequency on every continent. The world's largest protected areas of savannas are found in monsoonal northern Australia. These include relatively intact, tall, open forests where traditional indigenous fire regimes have been largely replaced in the past half century by contemporary patterns with trees experiencing fire as often as three out of five years. Eucalypt canopy trees form the basic structure of these savannas and changes to the canopy due to fire regimes cascade to affect other plants and animals. In this study, we used data from nearly three decades of field studies on the effects of fire on individual trees to define eight life‐history stages and to calculate transition rates among stages. We developed a stage‐based matrix population model that explicitly considers how fire season and understory influence growth, survival, and recruitment for each life‐history stage. Long‐term population growth rates and transient population dynamics were calculated under five different fire regimes, each in two understory types, using both deterministic and stochastic simulations of seasonal timing of fires. We found that fire was necessary for long‐term persistence of eucalypt canopy tree populations but, under annual fires, most populations did not survive. Population persistence was highly dependent on fire regime (fire season and frequency) and understory type. A stochastic model tended to yield higher population growth rates than the deterministic model with regular, periodic fires, even under the same long‐term frequency of fires. Transient population dynamics over 100 yr also depended on fire regime and understory, with implications for savanna physiognomy and management. Model predictions were tested in an independent data set from a 21‐yr longitudinal field study in Kakadu National Park. This study is a novel and integrative contribution to our understanding of fire in savanna biomes regarding the potential for long‐term persistence and transient dynamics of savanna canopy tree populations. The model is relatively simple, generalizable, and adaptable for further investigations of the population dynamics of savanna trees under fire.

Using reference sites to guide ecological engineering and restoration of an internationally significant uranium mine in the Northern Territory, Australia

Ranger uranium mine, surrounded by Kakadu National Park in northern Australia, is about to undertake broad-scale restoration of the first of its two pits and cease all mining and processing activities. Over the mine’s forty-year life information from two detailed vegetation maps and five significant reference site surveys has been used to assist with closure. All relevant and available data were reviewed and, as a result, biophysical, remote sensing and vegetation survey data, across an area known as the Georgetown analogue, were subsequently analysed in greater detail. Vegetation communities were assessed using cluster analysis, spatial analysis and regional scale fire mapping. Regional floristic patterns were reflected in vegetation survey data, but the frequency of fires in the assessed Georgetown analogue site was significantly lower to the landscape adjacent to most of the mine site. Indeed, reference ecosystems that capture the variability of fire regimes in the area surrounding the mine should be utilised in the future to provide further engineering and restoration guidance for the new landform, determine appropriate understory species and inform pathways for restoration success. Of the 44 over-storey species assessed in this study there is limited information on the propagation techniques for eighteen species, whilst the establishment of more than 40% of the species on unnatural, mine-created substrates is unknown. Therefore, a more complete list of plant species, knowledge of their propagation and establishment requirements, and appropriate spatial patterns are still needed to ensure that the restoration of Ranger Uranium mine will be successful.

Crop wild relatives seed conservation at Kakadu National Park

Crop wild relatives seed conservation at Kakadu National Park

Waging Paperfare: Subverting the Damage of Extractive Capitalism in Kakadu

ABSTRACTDrawing on campaigns waged and administrative burdens managed by the Gundjeihmi Aboriginal Corporation (GAC) in Kakadu National Park to manage the effects of existing uranium mining and further proposed mining, this article draws attention to some of the techniques and coalitions that GAC has created to manage its would‐be managers. It uses the case of monitoring the operations and particularly the rehabilitation of the Ranger Uranium mine and of halting the opening of a second mine, known as Jabiluka, to consider the less conspicuous paperwork battles that take place amid and in the aftermath of these public battles. In considering these contests, we argue that the double valency of holding to account needs to be considered, to avoid dichotomising Indigenous people as either co‐opted by or opposed to administration, a bifurcation which fails to recognize the complexity and inevitability of contemporary Indigenous management regimes. This is neither a celebration of Indigenous counter‐administration, nor a false positing of Aboriginal alternatives to institutionalized worlds. Concluding, we note that when the organizational toil of drawing the locus of power in decision‐making towards Aboriginal interests is made apparent, the notion that there is an alternative to institutionalized forces of settler colonialism, represented by Indigenous resistance, is complicated. We mark this organizational work as evidencing the unrelenting nature of administrative violence under active colonization.

Estuarine crocodiles in a tropical coastal floodplain obtain nutrition from terrestrial prey.

The estuarine crocodile (Crocodylus porosus) is one of the largest and most widespread crocodilians in the world. Although considered an apex species, the role of the estuarine crocodile in aquatic foodwebs is poorly understood; we know what crocodiles ingest, but not what nourishes them. In this study, we used a combination of stable isotope measurements (δ13C, δ15N, and δ34S) and direct feeding observations to identify the source of nutrition of estuarine crocodiles in Kakadu National Park, Northern Australia. Our results show that most crocodiles sampled (size 850 – 4200mm, with 76% of them being > 2.5 m) consume a large variety of prey, however a large proportion of their nutrition is derived from terrestrial prey. Introduced species such as water buffaloes (Bubalus bubalis) and pigs (Sus scrofa) could contribute between 53 and 84% to the nutrition of the sampled crocodiles. The isotopic composition of large crocodiles (total length > 3 m) suggested possible increase in marine prey consumption with size (R2 = 0.30; p = 0.005). Additionally, we found crocodiles sampled in the dry season had on average higher terrestrial contributions compared to crocodiles sampled during the wet season (84.1 ± 2.4% versus 55.4 ± 7.0%). Overall, we found that terrestrial prey are important source of nutrition for many crocodiles in this region where introduced herbivorous mammals are abundant.

A spatial vulnerability assessment of monsoonal wetland habitats to para grass invasion in Kakadu National Park, northern Australia

Kakadu National Park and its wetlands are World Heritage and Ramsar listed and are at risk from invasive grasses. However, it appears that not all habitats and native vegetation are equally at risk. We conduct a spatial risk assessment for para grass (Urochloa mutica) invasion across seasonally inundated habitats of the 258 km2 Magela Creek floodplain within Kakadu National Park using Landsat 5 TM time-series imagery. Two maps, representing water depth and fire history, were derived from the imagery using object-based image analyses. Depth was modelled using a linear regression relationship established between 254 known water depth locations and the multi-date spectral index values of segmented image objects at corresponding locations (R2 = 0.67; p < 0.0001). Binary fire-scar maps were then produced for each year of a 10-year period using visual interpretation and nearest neighbour classification. A map of the incidence of annual fire over this period was then calculated from the sum of the maps, overlaid. The maps were integrated in a GIS with an existing Landsat vegetation map to measure spatial inter-relationships between para grass, native vegetation, depth and fire. With a highly clustered distribution pattern, para grass occupied 1388 ha or 6% of the total floodplain area. However, its optimal depth habitat, estimated to be from 1.1 to 1.4 m, occurred over a much larger area (7180 ha) or 30% of the floodplain. Only 2% of this optimal area was actually occupied by para grass. Together the low occupancy of ‘optimal-depth’ habitat and a highly clustered distribution of para grass strongly suggested that, if left uncontrolled, it has capacity to spread further and eventually occupy much larger areas of this floodplain at high density. Landsat provided spatial information of suitable scale and accuracy to understand the landscape ecology of para grass; and from which to design and conduct further research, or trial management interventions to protect wetland vegetation at risk to weed invasion.

Declining populations in one of the last refuges for threatened mammal species in northern Australia

AbstractAustralia has contributed a disproportionate number of the world's mammal extinctions over the past 200 years, with the greatest loss of species occurring through the continent's southern and central arid regions. Many taxonomically and ecologically similar species are now undergoing widespread decline across the northern Australian mainland, possibly driven by predation by feral cats and changed fire regimes. Here, we report marked recent declines of native mammal species in one of Australia's few remaining areas that support an intact mammal assemblage, Melville Island, the largest island off the northern Australian coast. We have previously reported a marked decline on Melville Island of the threatened brush‐tailed rabbit‐rat (Conilurus penicillatus) over the period 2000–2015, linked to predation by feral cats. We now report a 62% reduction in small mammal trap‐success and a 36% reduction in site‐level species richness over this period. There was a decrease in trap‐success of 90% for the northern brown bandicoot (Isoodon macrourus), 64% for the brush‐tailed rabbit‐rat and 63% for the black‐footed tree‐rat (Mesembriomys gouldii), but no decline for the common brushtail possum (Trichosurus vulpecula). These results suggest that populations of native mammals on Melville Island are exhibiting similar patterns of decline to those recorded in Kakadu National Park two decades earlier, and across the northern Australian mainland more generally. Without the implementation of effective management actions, these species are likely to be lost from one of their last remaining strongholds, threatening to increase Australia's already disproportionate contribution to global mammal extinctions.

What do predator diets tell us about mammal declines in Kakadu National Park?

Context Small- and medium-sized native mammals have suffered severe declines in much of northern Australia, including within protected areas such as Kakadu National Park. Several factors have been implicated in these declines but predation, particularly by feral cats (Felis catus), has been identified as potentially the most direct cause of decline for many species. Aims We evaluated how prey frequency changed in cat and dingo scats in Kakadu from the early 1980s to 2013–15, with this period spanning a severe decline in the small- and medium-sized mammal fauna. Methods Chi-square test of independence and Fisher’s exact test were used to compare prey frequencies between dingoes and cats, and among years to assess significance of temporal change. Key results Small-sized native mammals were the prey item occurring at the highest frequency in scats for both dingoes and cats in the 1980s. Prey content in dingo and cat scats differed in the 2010s with macropods predominating in the scats of dingoes, and medium-sized native mammals predominating in cat scats. The frequency of occurrence of small-sized native mammals declined in both dingo and cat scats between the 1980s and 2010 sampling periods, while the frequency of occurrence of medium-sized native mammals remained constant in dingo scats and increased in cat scats. Conclusions Small mammals were a major component of the diets of both dingoes and cats in Kakadu in the 1980s, when small mammals were much more abundant. Despite marked reduction from the 1980s to the 2010s in the capture rates of both small- and medium-sized native mammals, some species continue to persist in the diets of cats and dingoes at disproportionally high frequencies. Both predators continue to exert predatory pressure on mammal populations that have already experienced substantial declines. Implications Although predation by feral cats is a major threat to small- and medium-sized native mammals, dingoes may also play an important role in limiting their recovery. Disturbance from fire and grazing by introduced herbivores has been shown to augment predatory impacts of feral cats on native mammals. Predation more generally, not just by feral cats, may be exacerbated by these disturbance processes. Management programs that solely focus on mitigating the impact of feral cats to benefit threatened species may be inadequate in landscapes with other significant disturbance regimes and populations of predators.

What was the vegetation in northwest Australia during the Paleogene, 66–23million years ago?

Fossil pollen and spores preserved in drillcore from both the upper South Alligator River (SARV) in the Kakadu National Park, Northern Territory and the North-West Shelf, Western Australia provide the first record of plants and plant communities occupying the coast and adjacent hinterland in north-west Australia during the Paleogene 66 to 23million years ago. The palynologically-dominant woody taxon is Casuarinaceae, a family now comprising four genera of evergreen scleromorphic shrubs and trees native to Australia, New Guinea, South-east Asia and Pacific Islands. Rare taxa include genera now mostly restricted to temperate rainforest in New Guinea, New Caledonia, New Zealand, South-East Asia and/or Tasmania, e.g. Dacrydium, Phyllocladus and the Nothofagus subgenera Brassospora and Fuscospora. These appear to have existed in moist gorges on the Arnhem Land Plateau, Kakadu National Park. No evidence for Laurasian rainforest elements was found. The few taxa that have modern tropical affinities occur in Eocene or older sediments in Australia, e.g. Lygodium, Anacolosa, Elaeagnus, Malpighiaceae and Strasburgeriaceae. We conclude the wind-pollinated Oligocene to possibly Early Miocene vegetation in the upper SARV was Casuarinaceae sclerophyll forest or woodland growing under seasonally dry conditions and related to modern Allocasuarina/Casuarina formations. There are, however, strong floristic links to coastal communities growing under warm to hot, and seasonally to uniformly wet climates in north-west Australia during the Paleocene-Eocene.

Sea-level rise in northern Australia's Kakadu National Park: a survey of floodplain eukaryotes

Forecasted climate-change models predict that much of northern Australia’s coastal habitats will be in retreat because of saltwater intrusion (SWI) from sea-level rise. A region of primary concern is the nutrient-rich and biodiverse floodplains of world heritage-listed Kakadu National Park (KNP). To understand the implications of SWI, we need fundamental baseline information for floodplain biota from the South Alligator River, KNP, northern Australia, and informative data on how increased and prolonged exposure to salt is likely to shape the eukaryotic community. To assist in addressing these key knowledge gaps, we used amplicon sequencing to examine the composition of eukaryotic soil communities from the South Alligator River floodplain, an ecologically important area at the ‘coalface’ of sea-level rise. Samples were obtained from three river zones and three floodplain morphologies, capturing a wide range of habitats and episodic exposures to both saltwater and freshwater. We found that both the floodplain morphology and positioning along the river significantly influenced eukaryotic composition. However, the influence of these variables varied greatly among the floodplain morphologies, with correlative evidence suggesting that both salinity and pH played a dominant role in shaping communities within lower parts of the floodplain, with this being particularly evident in those regions subjected to major tidal influence (estuarine funnel and sinuous, and cuspate).

Defining the importance of ecological processes for monitoring aquatic habitats for conservation and rehabilitation objectives at the Ranger uranium mine, Kakadu Region, Australia

Key ecological processes must be present and maintained in ecosystems to ensure the success of ecological restoration and conservation programs. The present paper identifies and defines key ecological processes operating at various spatial scales within aquatic ecosystems of the Magela Creek catchment, within Kakadu National Park, and prioritises those that may be vulnerable to potential mine-derived stressors. This assessment was required to ensure that current and future environmental monitoring programs are in place to safeguard the protection of these processes, particularly in the context of rehabilitation of Ranger uranium mine. Ecological processes within riparian habitats and biotic interactions across all habitats were at a higher risk of exposure to potential stressors. Generally, the selected assessment endpoints used for the operational phase of the mine are sufficient to measure and assess ecological processes. However, biological endpoints require additional suitable early detection indicators because marked lags exist in their response, which will be more important during the rehabilitation phase of the mine because of the longer timeframes to be assessed. The lags would otherwise allow potential impacts to underpinning processes to pass undetected. Risk identification allows monitoring programs to move beyond simple measurement variables to full evaluation of underlying ecological processes, which maintain both structure and function in ecosystems.

Historical perspectives on the mangroves of Kakadu National Park

Mangroves are a major ecosystem within Kakadu National Park in Australia’s Northern Territory, providing coastal protection, high biodiversity and an important resource for Aboriginal people. In the late Holocene (from c. 6000 before present), mangroves occupied much of the estuarine and coastal plains, but their range has subsequently contracted to the main river systems (the West Alligator, South Alligator and East Alligator Rivers, and the Wildman River), tributary creeks and offshore islands (Field and Barrow Islands). On the basis of maps of mangrove extent generated from aerial photography (1950, 1975, 1984 and 1991), compact airborne spectrographic imagery (CASI; 2002), light detection and ranging (LIDAR; 2011) and RapidEye data (2014 onward), changes in net area have been minor but significant redistribution has occurred, with this being attributed to both inland intrusion and seaward colonisation of mangroves. The greatest area changes have been associated with lower-stature mangroves dominated by Avicennia marina and Sonneratia alba, as determined from these datasets. Aerial surveys, conducted using a remote piloted aircraft (RPA) and fixed wing aircraft in September 2016, showed dieback of mangroves, with spaceborne RapidEye observations suggesting this occurred between late 2015 and 2016 and at the same time as the extensive mangrove losses reported in the Gulf of Carpentaria. Given the recent dieback and the associated need to better monitor and protect mangroves and proximal ecosystems in the World Heritage- and Ramsar-listed Kakadu National Park, the study recommends the development and implementation of a robust and long-term monitoring system that better utilises existing and ongoing earth observation and ground data, and is supported by a national approach.

Fire-Driven Decline of Endemic Allosyncarpia Monsoon Rainforests in Northern Australia

Although contemporary fire regimes in fire-prone Australian savannas are recognised as having major impacts on an array of biodiversity and environmental values, a number of studies have observed significant monsoon rainforest expansion in recent decades. Here we assess the status of a locally extensive endemic monsoon rainforest type, dominated by Allosyncarpia ternata (Myrtaceae), restricted to sandstone terrain including in the World Heritage property, Kakadu National Park. We undertook assessments of: (1) geographic correlates of Allosyncarpia forest distribution; (2) change in canopy cover at 40 representative forest patches at topographically exposed sites with reference to a 60-year aerial photo and fine-scale image archive, and fire mapping data; and (3) structural characteristics associated with sites exhibiting stable, contracting, and increasing canopy cover. Mean canopy cover at sampled forest patches declined by 9.5% over the study period. Most canopy loss occurred at the most fire-susceptible patches. Assessment of structural characteristics at sampled sites illustrated that canopy expansion represented vegetative recovery rather than expansion de novo. The study (1) confirms the vulnerability of exposed margins of this forest type to fire incursions; (2) illustrates the magnitude of, and describes solutions for addressing, the regional conservation management challenge; and (3) serves as a reminder that, in savanna environments, severe fire regimes can substantially outweigh the woody growth-enhancing effects of other regional (e.g., increased rainfall) and global-scale (e.g., atmospheric CO2 fertilisation) drivers.

Out of the frying pan: Reintroduction of toad‐smart northern quolls to southern Kakadu National Park

AbstractInvasive species are a leading cause of native biodiversity loss. In Australia, the toxic, invasive cane toad Rhinella marina has caused massive and widespread declines of northern quolls Dasyurus hallucatus. Quolls are fatally poisoned if they mistakenly prey on adult toads. To prevent the extinction of this native dasyurid from the Top End, an insurance population was set up in 2003 on two toad‐free islands in Arnhem Land. In 2015, quolls were collected from one of these islands (Astell) for reintroduction. We used conditioned taste aversion to render 22 of these toad‐naïve quolls toad averse. Seven quolls received no taste aversion training. The source island was also predator‐free, so all quolls received very basic predator‐aversion training. In an attempt to re‐establish the mainland population, we reintroduced these 29 northern quolls into Kakadu National Park in northern Australia where cane toads have been established for 13 years. The difference in survival between toad‐averse and toad‐naive quolls was immediately apparent. Toad‐naive quolls were almost all killed by toads within 3 days. Toad‐averse quolls, on the other hand, not only survived longer but also were recorded mating. Our predator training, however, was far less effective. Dingo predation accounted for a significant proportion of toad‐smart quoll mortality. In Kakadu, dingoes have been responsible for high levels of quoll predation in the past and reintroduced animals are often vulnerable to predation‐mediated population extinction. Dingoes may also be more effective predators in fire degraded landscapes. Together, these factors could explain the extreme predation mortality that we witnessed. In addition, predator aversion may have been lost from the predator‐free island populations. These possibilities are not mutually exclusive but need to be investigated because they have clear bearing on the long‐term recovery of the endangered northern quoll.

Efficacy of remote underwater video cameras for monitoring tropical wetland fishes

Remote underwater video (RUV) cameras are commonly used in marine environments to sample fish, but to date have infrequently been used in freshwater environments. We tested the utility of a range of underwater video camera deployments (floating/benthic and fixed/moving) for surveying fish assemblages within tropical wetland habitats of Kakadu National Park, Australia. RUV cameras in both fixed and moving configurations were able to detect a range of fish species in various habitat types, with shy and/or flighty species readily detected. Cameras also performed well in a variety of conditions, although dense macrophytes posed a challenge for all video deployment types. RUV camera survey data compared favourably to two traditional fish survey techniques (visual census and pop netting). However, fixed camera deployments more closely resembled data collected via traditional techniques; whereas moving RUV deployments were consistently lower than any other method. We find that RUV cameras are a valuable monitoring and sampling technique for assessing freshwater fish assemblages in tropical wetlands, and are especially useful where remoteness, difficult access, variable water quality, complex habitats and interactions between humans and dangerous aquatic life can limit the use of other traditional fish sampling techniques.

Understanding climate-change adaptation on Kakadu National Park, using a combined diagnostic and modelling framework: a case study at Yellow Water wetland

This paper describes a semi-quantitative approach for the assessment of sea-level rise (SLR) impacts on social–ecological systems (SES), using Yellow Water wetland on Kakadu National Park as a case study. The approach includes the application of a diagnostic framework to portray the existing SES configuration, including governance structures, in combination with qualitative modelling and Bayesian belief networks. Although SLR is predicted to cause saltwater inundation of freshwater ecosystems, cultural sites and built infrastructure, our study suggested that it may provide also an opportunity to bring together Indigenous and non-Indigenous knowledge and governance systems, towards a commonly perceived threat. Where feasible, mitigation actions such as levees may be required to manage local SLR impacts to protect important freshwater values. In contrast, adaptation will require strategies that facilitate participation by Kakadu Bininj (the Aboriginal people of Kakadu National Park) in research and monitoring programs that enhance understanding of salinity impacts and the adaptive capacity to respond to reasonably rapid, profound and irreversible future landscape-scale changes.

Declines in the mammal assemblage of a rugged sandstone environment in Kakadu National Park, Northern Territory, Australia

There has been marked recent decline in the terrestrial mammal fauna across much of northern Australia, with most documentation of such decline for lowland areas. Here we report changes in the assemblage of small mammals in a rugged sandstone environment (Nawurlandja, in Kakadu National Park) over intermittent sampling between 1977 and 2002. Four native mammal species were commonly recorded in the original sampling: sandstone antechinus (Pseudantechinus bilarni), northern quoll (Dasyurus hallucatus), Arnhem rock-rat (Zyzomys maini) and common rock-rat (Z. argurus). Trap success rates declined significantly for the northern quoll, Arnhem rock-rat and all species combined, but increased for the common rock-rat. Despite being recorded commonly in the initial (1977–79) study, no Arnhem rock-rats were recorded in the most recent (2002) sampling. Trap success rates for northern quoll declined by ~90% from 1977–79 to 2002. The reasons for change are not clear-cut. Notably, all sampling occurred before the arrival of cane toads (Rhinella marina), a factor that has caused severe decline in northern quoll numbers elsewhere. Fire was more frequent in the sampling area in the period preceding the 2002 sampling than it was in the period preceding the initial (1977–79) sampling, and this may have contributed to change in mammal abundance.