Adelaide River Research Articles

Rapid assessment of adult abundance and demographic connectivity from juvenile kin pairs in a critically endangered species

The viability of spatially structured populations depends on the abundance and connectivity between subpopulations of breeding adults. Yet, for many species, both are extremely difficult to assess. The speartooth shark is a critically endangered elasmobranch inhabiting tropical rivers with only three adults ever recorded in Australia. Close-kin mark-recapture models, informed by sibling pairs among 226 juveniles, were developed to estimate adult abundance and connectivity in two Australian river systems. Sixty-eight sibling pairs were found, and adult abundance was estimated at 892 for the Adelaide River and 1128 for the Alligator Rivers. We found strong evidence for female philopatry, with most females returning to the same river to pup. Adelaide River males appear largely philopatric, whereas Alligator Rivers males are highly connected to the Adelaide River. From only 4 years of sampling, our results demonstrate that juvenile-only kin pairs can inform simultaneous estimates of abundance and connectivity in a rare and threatened species.

Establishment of Siamese Fighting Fish on the Adelaide River floodplain: the first serious invasive fish in the Northern Territory, Australia

Siamese Fighting Fish Betta splendens is a well-known and popular aquarium fish. The species has recently invaded the Adelaide River floodplain, near Darwin in northern Australia. A very large and extensive population has persisted over consecutive years, with potential for further spread. This represents the first serious alien fish species incursion in the Northern Territory, with reports previously limited mainly to livebearers and cichlids in isolated habitats, some of which have been controlled by specific actions reviewed herein. The invasion highlights the need to maintain and strengthen proactive management, community engagement, and coordinated strategies for vectors of introduction including aquarium fishes.

Presence of Apis Rhabdovirus-1 in Populations of Pollinators and Their Parasites from Two Continents.

The viral ecology of bee communities is complex, where viruses are readily shared among co-foraging bee species. Additionally, in honey bees (Apis mellifera), many viruses are transmitted – and their impacts exacerbated – by the parasitic Varroa destructor mite. Thus far, the viruses found to be shared across bee species and transmitted by V. destructor mites are positive-sense single-stranded RNA viruses. Recently, a negative-sense RNA enveloped virus, Apis rhabdovirus-1 (ARV-1), was found in A. mellifera honey bees in Africa, Europe, and islands in the Pacific. Here, we describe the identification – using a metagenomics approach – of ARV-1 in two bee species (A. mellifera and Bombus impatiens) and in V. destructor mites from populations collected in the United States and Israel. We confirmed the presence of ARV-1 in pools of A. mellifera, B. impatiens, and V. destructor from Israeli and U.S. populations by RT-PCR and found that it can reach high titers in individual honey bees and mites (107–108 viral genomic copies per individual). To estimate the prevalence of ARV-1 in honey bee populations, we screened 104 honey bee colonies across Israel, with 21 testing ARV-1-positive. Tagged-primer-mediated RT-PCR analysis detected the presence of the positive-sense ARV-1 RNA in A. mellifera and V. destructor, indicating that ARV-1 replicates in both hosts. This is the first report of the presence of ARV-1 in B. impatiens and of the replication of a rhabdovirus in A. mellifera and V. destructor. Our data suggest that Varroa mites could act as an ARV-1 vector; however, the presence of ARV-1 in B. impatiens (which are not parasitized by Varroa) suggests that it may not require the mite for transmission and ARV-1 may be shared among co-foraging bee species. Given that ARV-1 is found in non-Apis bee species, and because “ARV” is used for the Adelaide River virus, we propose that this virus should be called bee rhabdovirus 1 and abbreviated BRV-1. These results greatly expand our understanding of the diversity of viruses that can infect bee communities, though further analysis is required to determine how infection with this virus impacts these different hosts.

Recreational fishing impacts on threatened river sharks: A potential conservation issue

SummaryThe Adelaide River in Australia's Northern Territory is a popular recreational fishing area, as well as habitat for threatened and protected river sharks (Glyphis species). Both the Critically Endangered Speartooth Shark (Glyphis glyphis) and Endangered Northern River Shark (Glyphis garricki) are identified here in illegal catches from recreational angling. The identification of a decayed shark specimen using a DNA barcoding‐like approach is the first such application to the identification of protected sharks in a recreational fishery. While the extent of catches by recreational anglers is unknown, the threatened status of these sharks, their suspected low population sizes, restricted distributions and importance of the Adelaide River as a nursery area call for the consideration of this as a potential conservation issue. As such, appropriate measures should be taken to reduce interactions with recreational anglers. The primary target species in the river is the iconic sportfish, Barramundi, which is predominantly caught by unbaited lure. Sharks are rarely caught on lure, allowing an opportunity for mitigation to focus on a fishing activity (baited hooks) which would limit any regulatory impact on popular lure fishing. Potential mitigation measures range from increased angler education and compliance checks, to the implementation of a spatial closure to baited hook fishing (a lure‐only zone). Such measures may assist in meeting a stated objective of the Australian Government's river shark Recovery Plan to ‘reduce and, where possible, eliminate adverse impacts of recreational fishing'.

Salinity and spawning of nurseryfish, Kurtus gulliveri, in the Adelaide River of northern Australia with notes on electrofishing and photos of a male carrying eggs

Nurseryfish are unique among fishes in that the males carry the fertilized eggs on a supraoccipital hook on their head. In an attempt to learn where, when, and at what salinities spawning occurs, an ichthyoplankton net was towed at 14 stations in the Adelaide River from the mouth (38 ppt) to the most upstream sections of the river (0.1 ppt). Larval nurseryfish (5–27.5 mm SL) were collected, preserved and measured, and water chemistry parameters were recorded with each sample. Larvae were found in the mid-reaches of the river during July–October, most commonly at salinities between 13.6–0.5 ppt. Salinities increased as the dry season progressed. Larvae were not taken at salinities higher than 19 ppt, nor did they occur in the upper-most reaches of the river system during this time of the dry season. What nurseryfish do and where they occur during the massive influx of freshwater runoff during the wet season (November–April) remains a mystery. Electrofishing for nurseryfish proved to be ineffective in the Adelaide River due to its extraordinary turbidity which made recovery of stunned fish difficult and fresh material of males carrying eggs remains elusive. Two historic photographs showing males carrying eggs are described.

The accelerating invasion: dispersal rates of cane toads at an invasion front compared to an already-colonized location

Evolutionary theory predicts that individuals at an expanding range edge will disperse faster than conspecifics in long-colonized locations, but direct evidence is rare. Previous reports of high rates of dispersal of cane toads (Rhinella marina) at the invasion front have been based on studies at a single site in the Northern Territory. To replicate the earlier work, we radio-tracked free-ranging toads in the Kimberley region of northwestern Australia (at the westward-spreading invasion front) and 500 km northeast, on the Adelaide River floodplain of the Northern Territory (where toads had already been present for 6 years). For comparison, we also radio-tracked native frogs (Litoria caerulea and L. splendida) at the same sites. Consistent with the earlier reports, invasion-front cane toads travelled further per day, were more highly directional, and re-used refuge sites less frequently, than did conspecifics from an already-colonized site. In contrast, native frogs showed similar movement patterns in the two study areas. Our results confirm previous reports, and suggest that accelerated dispersal may be a common feature of individuals at the vanguard of a biological invasion.

Larval nurseryfish, Kurtus gulliveri (Perciformes : Kurtidae), in the Adelaide River of the Northern Territory: their season, fellow travellers and unusual rib anatomy

This study was undertaken to determine the spawning season of the nurseryfish, a species with a unique method of parental care found only in northern Australia and southern New Guinea. Monthly samplings with an ichthyoplankton net at the same locality in the Adelaide River over multiple years yielded no larval nurseryfish in February, March, April and May. Larvae first appeared in June and were collected each month until January. From this we conclude that the nurseryfish spawning season in the Adelaide River is June–January. Twelve other larval fish species from 10 families were collected in the plankton tows with nurseryfish. Larval nurseryfish are readily identified and separated from other larval fishes by their peculiar rib anatomy, an important diagnostic character of Kurtus. The development of the unusual rib anatomy is examined with three-dimensional micro-computerised tomography scans of 12–21-mm standard length (SL) specimens. The bony protection of the swim bladder formed by the ribs is visible in the smallest postflexion specimens examined and is essentially complete by 19 mm SL. These ecological and anatomical observations add another pixel to the big picture of nurseryfish life history.

The endoparasites of Liasis fuscus (Serpentes : Boidae) from the Adelaide River floodplain, Northern Territory, Australia

This study documents the parasite assemblage of Liasis fuscus Peters, 1873 from the Adelaide River flood plain, Northern Territory, Australia. In total, nine species of helminth (comprising three cestodes and six nematodes), one pentastome and one protozoan were found in 180 water pythons, with the Nematoda being the dominant and most diverse group, and a cestode, Bothridium ornatum Maplestone & Southwell, 1923, the most prevalent species. In spite of the hosts being present in high numbers the helminth assemblage was depauperate, characterised by low prevalence, intensity, frequency and abundance of species, with neither season nor sex of host affecting abundance. There were, however, significant differences between ages of hosts, juveniles having fewer parasites, and seasonal diversity, with the wet season of 2004 and the dry of 2005 the most similar. Of the Australian python species analysed Morelia spilota (Lacépède, 1804) had the highest species richness. The lower species richness found in L. fuscus was possibly due to its unusual biology. Biogeographic relationships of the parasite fauna of L. fuscus are diverse, connections with Africa, Asia, and South America being noted.

Rediscovery of the rust Diabole cubensis, released as a classical biological control agent against the invasive weed Mimosa pigra in Australia

The neotropical rust Diabole cubensis was introduced as a biological control agent against the weed Mimosa pigra in the Northern Territory during the period 1996–1999. It was thought to have failed to establish as it had not been observed since then. In 2011, D. cubensis was detected on M. pigra plants on the Finniss River and Daly River floodplains, 12 years after its introduction. In 2012, the fungus was also detected on the Mary and Adelaide River floodplains. Details of these findings, a description and illustrations of the rust fungus are included.

Kotonkan and Obodhiang viruses: African ephemeroviruses with large and complex genomes

Kotonkan virus (KOTV) and Obodhiang virus (OBOV) are rhabdoviruses that were isolated from arthropods in Africa and formerly classified as lyssaviruses. KOTV causes clinical bovine ephemeral fever in cattle; the ecology and pathogenicity of OBOV is poorly understood. In this paper, we report the complete genome sequences of KOTV and OBOV, their gene expression profiles, and their serological and phylogenetic relationships to other rhabdoviruses. The 15,870 nt KOTV genome (3′-l-N-P-M-G-GNS-α1-α2-β-γ-δ-L-t-5′) is similar to that of bovine ephemeral fever virus but encodes an additional protein (δ) that shares homology with the pleckstrin homology domain of coactivator-associated arginine methyltransferase. The 14,717 nt OBOV genome (3′-l-N-P-M-G-GNS-α1-α2-β-L-t-5′) is similar to that of Adelaide River virus from which it is distinguishable serologically. In each virus, all ORFs, except α1 and α2, are transcribed as monocistronic mRNA. Genetic and serological data indicate that KOTV and OBOV should be classified as new species in the genus Ephemerovirus.

Low genetic diversity in nurseryfish, 'Kurtus gulliveri' (Perciformes: Kurtidae), and an appraisal of its breeding system using microsatellite loci

The Nurseryfish, Kurtus gulliveri, is a freshwater fish distributed in northern Australia and southern New Guinea that exhibits forehead brooding, a unique form of male parental care. Microsatellite markers were developed for paternity analysis to study its reproductive life history in a population from the Adelaide River, Northern Territory, Australia. In 20 microsatellite loci tested, only two polymorphic markers were found. The microsatellite data are mostly consistent with the hypotheses that the putative egg-carrying male sired the egg mass and no multiple paternity occurred in the population examined. However, caution should be taken in interpreting the results, given the low genetic diversity and limited analytical power. The extremely low genetic diversity was also corroborated by mitochondrial DNA, the most variable fragment in the piscine mitogenome. Eighteen individuals from the Adelaide River were sequenced, revealing four polymorphic sites in the control region and five haplotypes in total, with an average p-distance of 0.001. Additional individuals from three other isolated populations in the Northern Territory (Daly River, South Alligator River and East Alligator River) were sequenced and found to be identical to one of the common haplotypes from the Adelaide River. Four specimens collected from New Guinea represent a single haplotype that had 24.5 substitutions, on average, relative to the Australian populations.

Clarification of field characters for three freshwater sharks and a photographic atlas of 'Glyphis glyphis' and 'G. garricki' from the Adelaide River, Northern Territory, Australia

Eighty-two Glyphis glyphis, one G garricki and two Carcharhinus leucas were caught at six localities in the Adelaide River on 66 gill-netting trips from mid-May to mid-December during 2001, 2003-05 and 2009. Photographs are presented that differentiate these euryhaline sharks. The small second dorsal fin of C. leucas clearly separates it from Glyphis species. The waterline (i.e. junction of dark dorsal and pale ventral colouration) on G glyphis extends just under the eye whereas it extends well below the lower margin of the eye in G garricki. Photographs showing shark bite marks on other species are presented. Because of the presence of G glyphis under 610 mm TL with umbilical scars, it is postulated that Marrakai Creek is a nursery area and an important juvenile habitat of this species especially from September-December.

Home Range and Movement Patterns of an Estuarine Crocodile 'Crocodylus porosus': A Satellite Tracking Pilot Study

The number of Estuarine Crocodiles 'Crocodylus porosus' in the Northern Territory, Australia is increasing. This has led to an increase in interaction with humans and livestock. Whilst there have been a number of studies on the distribution and movement of crocodiles in Australia, little has been recorded detailing movement patterns, and less evaluating the technical effectiveness of employing satellite tracking technology on this species. We attached an Argos satellite transmitter to a 4.2 m male Estuarine Crocodile captured in the Adelaide River, approximately 100 km east of Darwin, Northern Territory, Australia. During the six month study period (July to December 2005), the crocodile showed definite signs of home range fidelity, staying within a Minimum Convex Polygon of 63 km2 and a 95% kernel area of 8 km2. The average daily movement was 5.9 km day-1 with increased movement during the month of December. A high percentage of useable locations (65%) were received from the Platform Terminal Transmitter, with an increased number of location readings occurring between 2000 and 0700 hours. Given the aggressiveness of this species and the hostile environments in which they live, the Argos system is a useful method for tracking their movement. The results of this study have provided preliminary information improving our understanding of the home range and behaviour of a large male crocodile.

Predation on toxic cane toads (Bufo marinus) may imperil bluetongue lizards (Tiliqua scincoides intermedia, Scincidae) in tropical Australia

Context. Detecting ecological impacts of invasive species can be extremely difficult. Even major population declines may be undetectable without extensive long-term data if the affected taxon is rare and/or difficult to census, and exhibits stochastic variation in abundance as a result of other factors. Our data suggest such a situation in an iconic Australian reptile species, the bluetongue lizard. Originally restricted to Central and South America, cane toads (Bufo marinus) are rapidly spreading through tropical Australia. Most native predators have no evolutionary history of exposure to the toads’ distinctive chemical defences (bufadienolides), and many varanid lizards, elapid snakes, crocodiles and marsupials have been killed when they have attempted to consume toads. Aims. Scincid lizards have not been considered vulnerable to toad invasion; however, one lineage (the bluetongues, genus Tiliqua) consists of large omnivores that may be affected. Our field and laboratory research aimed to elucidate this concern. Methods. Nightly surveys for bluetongue lizards (Tiliqua scincoides intermedia) and cane toads were conducted along two adjacent roadways on the Adelaide River floodplain of the Northern Territory. Scent discrimination trials in the laboratory assessed lizard responses to chemical cues from three food types (native frogs, cane toads and ‘preferred foods’) by counting tongue-flicks and biting elicited by cotton swabs. A subset of lizards was presented with live toads. Key results. Numbers of bluetongues encountered during standardised field surveys in the Darwin region declined soon after toads arrived, and we have not recorded a single lizard for the last 20 months. In the laboratory, foraging responses of bluetongues were as intense to cane-toad scent as to the scent of native frogs, and many of the lizards we tested attempted to consume toads, and were poisoned as a result. Conclusions and implications. The population decline of bluetongues in this region appears to have been the direct result of fatal ingestion of toxic cane toads. Our studies thus add a scincid lizard species to the list of native Australian predators imperilled by cane-toad invasion, and point to the difficulty of detecting invader impact even for an iconic species in a system subject to detailed survey work.

Observations on the distribution, biology, short-term movements and habitat requirements of river sharks Glyphis spp. in northern Australia

The genus Glyphis comprises a group of rare and poorly known species. G. glyphis and G. garricki are found in northern Australia, and both species are listed as Critically Endangered C2a(i) on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. We collated all available records of G. glyphis and G. garricki in Australia to gain an understanding of the species’ distribution and biology. All records of G. glyphis (n = 106) were confined to 9 tropical rivers and estuaries north of 15°S. G. garricki (n = 32) were captured in 4 rivers and estuaries as well as in marine environments north of 18°S. Both species can be classified as euryhaline elasmobranchs. Parturition is thought to occur in October to December, and size at birth for both species is around 50 to 65 cm total length (TL). Two male G. garricki were mature at 142 and 144 cm TL, 2 females of 177 and 251 cm TL were mature, with the smaller animal having 9 early-stage embryos in utero. No mature G. glyphis have been recorded to date. Short-term movement patterns of 3 G. glyphis were investigated in the Adelaide River (Northern Territory) using acoustic tags. Animals were tracked for 27.8, 27.0 and 50.2 h respectively and displayed up- and downstream tidally assisted movement, moving on average 10 to 12 km per tide. The limited distribution, specific habitat requirements and repeated use of available habitat make Glyphis species particularly vulnerable to localised overfishing and habitat degradation. These findings highlight the need for additional research and the implementation of national recovery plans for both species

Spatial ecology of hatchling water pythons (Liasis fuscus) in tropical Australia

Abstract:Young snakes are rarely seen in the field and little is known about their habits, mostly because they are too small for radio-telemetry (the primary method for studying snake spatial ecology). However, the offspring of some larger species can be fitted with transmitters and we investigated the spatial ecology and habitat use of ten hatchling water pythons (Liasis fuscus: Pythonidae) in the floodplain of the Adelaide River, tropical Australia. Patterns of habitat use in the late wet season and during the dry season were similar to those of adults tracked in the same vicinity in an earlier study. Soon after release the young snakes moved to the floodplain, avoiding pasture areas. Diurnal refuge sites were typically in the base of grass clumps or below the soil surface, especially in sites with thick vegetation and deep, wide soil cracks. Adult snakes are more sedentary but move longer absolute distances (mean ± SE = 252 ± 50 m wk−1) than hatchlings (66.3 ± 41 m wk−1). However, hatchling snakes moved longer distances relative to body size (84.4 ± 1.1 body lengths wk−1) than did the previously studied adults (66.0 ± 1.1 body lengths wk−1). Mean and minimum body temperatures of the hatchlings were correlated with mean and minimum air temperatures, respectively.

Parasites of Rattus colletti (Rodentia:Muridae) from the Adelaide River floodplain, Northern Territory, and comparison with assemblages in other Rattus species

This study documents the parasite assemblage of Rattus colletti (Thomas, 1904) from the Adelaide River flood plain, Northern Territory, Australia. In total, six species of helminth (comprising two cestodes, one trematode and three nematodes), and four species of arthropod (comprising one tick, one mite, one flea (identified to family level) and one louse (identified to generic level)) were found. In spite of the hosts being present in high numbers the helminth assemblage was depauperate, characterised by low prevalence and abundance, both being higher in wet seasons. More helminths were found in larger animals. The most prevalent helminth was from the Trichostrongylina, Nippostrongylus typicus (Mawson, 1961). The assemblage was characterised as having two heirloom species (N. typicus and Hymenolepis diminuta (Rudolphi, 1819)), a host capture (Raillietina celebensis (Janicki, 1902) and a cosmopolitan species (Mastophorus muris (Gmelin, 1790)) as well as occasional infections. When compared with the helminths from a single population of Rattus sordidus (Gould, 1858) a similar number of species were found, three species being in common, and both were depauperate when compared with the more extensively surveyed faunas of Rattus fuscipes (Waterhouse, 1839) and Rattus leucopus (Gray, 1858).

Mass mortality of native anuran tadpoles in tropical Australia due to the invasive cane toad ( Bufo marinus)

Specific pathways of the ecological impact of invasive species remain poorly known. Although the spread of toxic cane toads ( Bufo marinus) through tropical Australia is widely believed to have caused extensive mortality of native reptiles and mammals, effects of toad ingestion on native anurans have been virtually ignored. Our studies on the Adelaide River floodplain show that the most numerous vertebrate victims of toad invasion are native tadpoles that die when they attempt to consume toad eggs. We documented 11 episodes of mass mortality, totalling >1300 tadpoles of 10 species, in five waterbodies within a single wet-season shortly after the toads invaded. A causal link between toad breeding and tadpole mortality is supported by observations that: (1) in at least 9 of the 11 waterbodies involved, toads bred immediately prior to mortality events; (2) water quality was indistinguishable from that of control ponds, and tadpoles placed in that water remained healthy; (3) dead tadpoles showed no sign of disease; and (4) laboratory trials showed rapid, 100% mortality in native tadpoles exposed to freshly-laid toad eggs. Despite these high mortality rates, toad invasion does not appear to threaten the viability of anuran populations because frogs often breed in ponds not used by toads, and because density-dependent growth and survival within tadpole communities mean that additional mortality may not reduce the total effective recruitment of metamorph frogs from a waterbody.

The spatial ecology of cane toads (Bufo marinus) in tropical Australia: Why do metamorph toads stay near the water?

Abstract Cane toads (Bufo marinus) have invaded large areas of Australia, killing many native predators as they have done so. The metamorph stage of the life cycle – the first terrestrial phase, immediately after transformation from the tadpole – is critical for ecological impact (because these animals are small enough to be prey for many native predators) and for potential control of toad populations (because small body size renders metamorphs vulnerable to desiccation). To quantify the spatial and temporal distribution of metamorph toads, and the biotic and abiotic factors that might affect their distributions, we surveyed toad breeding sites in Australia's wet‐dry tropics (Adelaide River floodplain, NT) in both the wet season and the dry season. Metamorphs were concentrated close to the water's edge during the dry season, especially at midday when desiccation rates were highest. During the wet season, metamorphs were widely dispersed through the landscape. Our surveys indicate that abiotic factors (risk of desiccation) are most favourable for metamorph toads close to the pond edge, but biotic factors (food supply, and risk of competition and cannibalism) are most favourable away from the water. Operative temperatures were spatially homogeneous and sublethal, and so are unlikely to influence metamorph distribution. Desiccation risk fluctuated on a diel cycle as well as seasonally. We predict that metamorph toads benefit from dispersing as soon as desiccation risk allows them to do so, and hence the distribution of metamorph toads will shift dynamically in response to weather‐mediated changes in rates of evaporative water loss.

A comparison of saltwater crocodile (Crocodylus porosus) populations in freshwater-floodplain and tidal river habitats of the Adelaide River catchment, Northern Territory, Australia

Because they are subject to commercial harvesting, Crocodylus porosus populations in Australia are monitored to detect trends in their population growth. Monitoring programs are restricted primarily to estuarine waters with high crocodile densities, subsequently little information is available on populations in freshwater habitats. In this study I compared the body-size structure and minimum number of C. porosus known to be alive in tidal-estuarine and freshwater-floodplain habitats of the lower Adelaide River catchment, Northern Territory (N.T.) during the 2004 dry season. A total of 669 C. porosus was sighted. Of these individuals, 546 (81.6%) were sighted in tidal-estuarine waters and 123 (18.4%) were sighted in freshwater, floodplain billabongs and creeks. Crocodiles were observed up to 17.3 km from tidal waters. Crocodiles less than 1.2 m total length (TL) were the most frequently sighted size category in both the freshwater-floodplain (68%), and tidal river (31%) populations. Crocodiles 1.2-3.4 m TL comprised 62% of those seen in the tidal river but only 22% of those in freshwater floodplain habitats. Crocodiles >3.4 m TL comprised 10% and 6.5% of the sighted population in freshwater-floodplain and tidal river habitats, respectively. The body-size structure of C. porosus inhabiting the freshwater floodplain and tidal river habitats of the Adelaide River differed markedly from that observed in marine and freshwater river habitats where crocodiles less than 1.2 m are rarely encountered.