Tropical Western Australia Research Articles

Polycyclic aromatic hydrocarbons in tropical Australian stalagmites: a framework for reconstructing paleofire activity

Human activity and climate change are altering natural rates and intensities of wildfire, but the scale and extent of burning prior to the modern era are poorly understood. Paleofire activity may be reconstructed using a variety of records (e.g., charcoal in lake sediments, burn scars on tree rings), but these are not available in all environmental settings. Here we investigate the utility of a novel paleofire proxy: trace pyrogenic organic compounds in stalagmites. Polycyclic aromatic hydrocarbons (PAHs) are linked to burning of biomass and are transported downward through soil and bedrock by infiltrating rainwater and incorporated into stalagmites in underlying caves where they are preserved. In order to test links between the stalagmite PAHs and fire above the cave, we performed a series of experiments using PAH distributions at KNI-51, a shallow cave located in tropical Western Australia, where bushfire is a regular occurrence. First, the possibility of surface contamination was evaluated by measuring PAH abundances and distributions in sequential digestions and by considering other possible additional sources, such as regional oil and gas fields or proximal combustion of fossil fuels. Second, PAHs were measured in soils above the cave and in sediments from the stalagmite chamber floor as possible sources of these organic compounds, and at near annual resolution in three aragonite stalagmites to evaluate the degree of deposition and conservation. Third, possible non-pyrogenic sources of organic compounds were evaluated through alkane distribution and specific m/z ratios. Fourth, signal replication of PAHs was tested in two coeval stalagmites. Fifth, satellite-mapped fire scars were used to examine the relationship between stalagmite PAH abundances and proximity of burning to the cave.The results support the hypothesis that PAHs in KNI-51 stalagmite carbonate reflect paleofire activity within 3 km of the cave, and thus that stalagmites can serve as an important new high resolution proxy for landscape-scale fire activity. Given that karst is present in many fire-prone environments, and that stalagmites can be precisely dated and may grow continuously for millennia, the potential utility of a stalagmite-based paleofire proxy is high.

A New Endemic Species of Milariconus Tucker & Tenorio, 2009 (Gastropoda: Conidae) from Western Australia

A new species of Miliariconus from tropical Western Australia, is described based on morphological differences with known taxa from that region. The new species differs from known Australian species in sculptural form and colour. This species further highlights the endemism of much of the new taxa that is being discovered in remote northern Australia.

Glacial origin of bat ensembles in tropical Western Australia

Western Australia’s tropical bat fauna comprises two communities; both are strict ensembles. One involves up to 19 species and occupies mangrove forest; the other, its landward counterpart, involves up to 22 species. Each includes habitat-generalist, productivity-dependent and cave-dependent species, so they achieve their full diversity in mangrove or riparian ecosystems associated with cavernous landscapes. Periods of significantly reduced rainfall are recognised in the climate record of the last ∼20 000 years, during which mangrove and upland riparian forests were the only highly productive ecosystems remaining in tropical Western Australia. During glacial cycles, these two refugia for mesic-adapted bats become geographically separated by the exposed continental shelf, a flat coastal plain more than 100 km wide. We review mangrove forests as evolutionary refuges during the Pleistocene, and use information on geographic range, endemism and habitat specificity to investigate the role of climatic and sea-level fluctuations in generating bat community structure. We conclude that mangrove forests provided a glacial refuge for all ensemble components; that the separation drove the evolution of two different ensembles. Northern Territory populations of Western Australia’s landward and mangrove specialists occupy landward as well as mangrove ecosystems, implying that mangrove refugia were not accessible during glacials.

Distribution of the Pearl Oyster Pinctada maxima off Eighty Mile Beach, Western Australia

The silver-lipped pearl oyster, Pinctada maxima, is the primary species used for the culture of pearls in the Indo-Pacific region. The Western Australian fishery relies on wild-caught animals, and as such, knowledge of the status and distribution of P. maxima underpins sustainable management of the fishery. Eighty Mile Beach, in tropical Western Australia, is the key harvest area for P. maxima, with oysters collected by divers to depths of ∼35 m, although there are anecdotal accounts of oysters beyond diving depths. Image-based, and acoustic methods were used to elucidate distribution patterns of P. maxima off Eighty Mile Beach, including data from 862 km2 of multibeam survey and 119 towed video transects spanning an area from the 20 to 100 m contour lines. We quantified habitat characters including depth, substrate, and benthic community composition associated with pearl oyster distribution. Multibeam sonar data was also coupled with towed video data to produce predictive statistical models of P. maxima habitat. We found P. maxima to depths of 76 m, although more than 90% of individuals occurred shallower than 40 m and less than 2% were found deeper than 50 m. Oysters occupied flat, sandy habitats with neighbouring benthic communities of filter feeders (>98% of observations). These results show P. maxima predominantly occurs in depths <40 m, with no evidence that extensive populations extend into deep water in the region.

More cautionary tales: family, generic and species synonymies of recentlypublished taxa of ghost and mud shrimps (Decapoda: Axiidea and Gebiidea).

Re-examination of the holotype of Neoaxius nicoyaensis Sakai, 2017 showed that it is conspecific with the axiid Guyanacaris caespitosa Squires, 1979 and thus Neoaxius Sakai, 2017 and Neoaxiidae Sakai, 2017 are respectively subjective junior synonyms of Guyanacaris Sakai, 2011 and Axiidae Huxley, 1879. The types and numerous specimens of the callianassid Trypaea vilavelebita Sakai Türkay, 2012 are juveniles of the common northeastern Atlantic-Mediterranean species, Callianassa subterranea (Montagu, 1808); the name is therefore a subjective junior synonym. The monotypic callianopsid genera Pleurocalliax Sakai, 2011, Neocallianopsis Sakai, 2011 and Phaetoncalliax Sakai, Türkay, Beuck Freiwald, 2015 are found not to differ from Callianopsis de Saint Laurent, 1973, the only alleged differences found to be untrue or trivial. Phaetoncalliax mauritana Sakai, Türkay, Beuck Freiwald, 2015 and Neocallianopsis africana Sakai, Türkay, Beuck Freiwald, 2015 are thereby transferred to Callianopsis, the latter a subjective junior synonym of the former. Contrary to the assertion of its author, the gourretiid Pseudogourretia portsudanensis Sakai, 2005, the only species in its genus, has no pleurobranchs. The genus Pseudogourretia Sakai, 2005 is therefore synonymised with Gourretia de Saint Laurent, 1973. The respective holotypes of Paracalliax stenophthalmus Sakai, Türkay, Beuck Freiwald, 2015 and Paracalliax bollorei de Saint Laurent, 1979 were re-examined. Both are from the Banc d'Arguin, off Mauritania, and are identical at the species level. The upogebiid Kuwaitupogebia nithyanandan Sakai, Türkay Al Aidaroos, 2015 from Kuwait is identical to Upogebia balmaorum Ngoc-Ho, 1990 from the Seychelles, Madagascar and tropical Western Australia. Kuwaitupogebia Sakai, Türkay Al Aidaroos, 2015 is therefore synonymised with Upogebia Leach, 1814 and Kuwaitupogebiidae Sakai, Türkay Al Aidaroos, 2015 with Upogebiidae Borradaile, 1903.

Deployable Molecular Detection of Arboviruses in the Australian Outback.

The most common causes of human infection from the arboviruses that are endemic in Australia are the arthritogenic alphaviruses: Ross River virus (RRV) and Barmah Forest virus (BFV). The most serious infections are caused by the neurotropic flaviviruses, Murray Valley encephalitis virus (MVEV) and the Kunjin subtype of West Nile virus. The greatest individual risk of arbovirus infection occurs in tropical/subtropical northern Australia because of the warm, wet summer conditions from December to June, where conventional arbovirus surveillance is difficult due to a combination of low population density, large distances between population centers, poor roads, and seasonal flooding. Furthermore, virus detection requires samples to be sent to Perth up to 2,000 km away for definitive analysis, causing delays of days to weeks before test results are available and public health interventions can be started. We deployed a portable molecular biology laboratory for remote field detection of endemic arboviruses in northern Queensland, then in tropical Western Australia and detected BFV, MVEV, and RRV RNA by polymerase chain reaction (PCR) assays of extracts from mosquitoes trapped in Queensland. We then used a field-portable compact real-time thermocycler for the samples collected in the Kimberley region of Western Australia. Real-time field PCR assays enabled concurrent endemic arbovirus distribution mapping in outback Queensland and Western Australia. Our deployable laboratory method provides a concept of operations for future remote area arbovirus surveillance.

Regional Changes in Earth's Color and Texture as Observed From Space Over a 15-Year Period

Earth-observing satellites provide global observations of many geophysical variables. As these variables are derived from measured radiances, the underlying radiance data are the most reliable sources of information for change detection. Here, we identify statistically significant trends in the color and spatial texture of the Earth as viewed from multiple directions from the Multi-angle Imaging SpectroRadiometer (MISR), which has been sampling the angular distribution of scattered sunlight since 2000. Globally, our results show that the Earth has been appearing relatively bluer (up to 1.6% per decade from both nadir and oblique views) and smoother (up to 1.5% per decade only from oblique views) over the past 15 years. The magnitude of the global blueing trends is comparable to that of uncertainties in radiometric calibration stability. Regional shifts in color and texture, which are significantly larger than global means, are observed, particularly over polar regions, along the boundaries of the subtropical highs, the tropical western Pacific, Southwestern Asia, and Australia. We demonstrate that the large regional trends cannot be explained either by uncertainties in radiometric calibration or variability in total or spectral solar irradiance; hence, they reflect changes internal to the Earth's climate system. The 15-year-mean true color composites and texture images of the Earth at both nadir and oblique views are also presented for the first time.

Time series analysis of RSV and bronchiolitis seasonality in temperate and tropical Western Australia

Respiratory syncytial virus (RSV) causes respiratory illness in young children and is most commonly associated with bronchiolitis. RSV typically occurs as annual or biennial winter epidemics in temperate regions, with less pronounced seasonality in the tropics. We sought to characterise and compare the seasonality of RSV and bronchiolitis in temperate and tropical Western Australia. We examined over 13 years of RSV laboratory identifications and bronchiolitis hospitalisations in children, using an extensive linked dataset from Western Australia. We applied mathematical time series analyses to identify the dominant seasonal cycle, and changes in epidemic size and timing over this period. Both the RSV and bronchiolitis data showed clear winter epidemic peaks in July or August in the southern Western Australia regions, but less identifiable seasonality in the northern regions. Use of complex demodulation proved very effective at comparing disease epidemics. The timing of RSV and bronchiolitis epidemics coincided well, but the size of the epidemics differed, with more consistent peak sizes for bronchiolitis than for RSV. Our results show that bronchiolitis hospitalisations are a reasonable proxy for the timing of RSV detections, but may not fully capture the magnitude of RSV epidemics.

Combining morphometrics with molecular taxonomy: How different are similar foliose keratose sponges from the Australian tropics?

Sponge taxonomy can be challenging as many groups exhibit extreme morphological plasticity induced by local environmental conditions. Foliose keratose sponges of the sub-family Phyllospongiinae (Dictyoceratida, Thorectidae: Strepsichordaia, Phyllospongia and Carteriospongia) are commonly found in intertidal and subtidal habitats of the Indo-Pacific. Lacking spicules, these sponges can be difficult to differentiate due to the lack of reliable morphological characters for species delineation. We use molecular phylogenies inferred from the nuclear Internal Transcribed Spacer 2 region (ITS2) and morphometrics (19 characters; 52 character states) to identify evolutionarily significant units (ESUs; sensu Moritz) within foliose Phyllosponginiids collected from seven geographic locations across tropical eastern and Western Australia. The ITS2 topology was congruent with the tree derived from Bayesian inference of discrete morphological characters supporting expected taxonomic relationships at the genus level and the identification of five ESUs. However, phylogenies inferred from the ITS2 marker revealed multiple sequence clusters, some of which were characterised by distinct morphological features and specific geographic ranges. Our results are discussed in light of taxonomic incongruences within this study, hidden sponge diversity and the role of vicariant events in influencing present day distribution patterns.

A Stalagmite record of Holocene Indonesian–Australian summer monsoon variability from the Australian tropics

Oxygen isotopic data from a suite of calcite and aragonite stalagmites from cave KNI-51, located in the eastern Kimberley region of tropical Western Australia, represent the first absolute-dated, high-resolution speleothem record of the Holocene Indonesian–Australian summer monsoon (IASM) from the Australian tropics. Stalagmite oxygen isotopic values track monsoon intensity via amount effects in precipitation and reveal a dynamic Holocene IASM which strengthened in the early Holocene, decreased in strength by 4 ka, with a further decrease from ∼2 to 1 ka, before strengthening again at 1 ka to years to levels similar to those between 4 and 2 ka. The relationships between the KNI-51 IASM reconstruction and those from published speleothem time series from Flores and Borneo, in combination with other data sets, appear largely inconsistent with changes in the position and/or organization of the Intertropical Convergence Zone (ITCZ). Instead, we argue that the El Niño/Southern Oscillation (ENSO) may have played a dominant role in driving IASM variability since at least the middle Holocene. Given the muted modern monsoon rainfall responses to most El Niño events in the Kimberley, an impact of ENSO on regional monsoon precipitation over northwestern Australia would suggest non-stationarity in the long-term relationship between ENSO forcing and IASM rainfall, possibly due to changes in the mean state of the tropical Pacific over the Holocene.

The status of non-volant mammals along a rainfall gradient in the south-west Kimberley, Western Australia

To assess the current status of mammals in relation to mean annual rainfall and to improve knowledge of the original mammalian assemblages in tropical Western Australia, extant terrestrial mammals and subfossil mammalian remains were sought along a rainfall gradient in two parallel ranges in the Kimberley, Western Australia. As expected, extant mammal species richness decreased with decreasing rainfall. Data from other studies in higher-rainfall areas complemented this conclusion and a parallel decline in trap success implied an overall decline in abundance, although numbers of two rodents (Rattus tunneyi and Zyzomys argurus) were highly variable. Small rodents were rare. Subfossil deposits were biased by accumulation processes, with most attributable to tytonid owls. They largely consisted of rodent and, to a lesser extent, small dasyurid bones and there was a high level of consistency in the proportional composition of many common species across the rainfall gradient. Most deposits appear to predate the introduction of stock in the 1880s and some may be much older. All species persist in the study area except two Notomys spp. and three Pseudomys spp. Both the Notomys and one Pseudomys are apparently undescribed, extinct species. However, there were marked ratio differences between subfossil and modern assemblages. Although specimens of species larger than those taken by tytonid owls were scarce, their occurrences were broadly consistent with the modern understanding of distributions.

Zucchini yellow mosaic virus: biological properties, detection procedures and comparison of coat protein gene sequences

Between 2006 and 2010, 5324 samples from at least 34 weed, two cultivated legume and 11 native species were collected from three cucurbit-growing areas in tropical or subtropical Western Australia. Two new alternative hosts of zucchini yellow mosaic virus (ZYMV) were identified, the Australian native cucurbit Cucumis maderaspatanus, and the naturalised legume species Rhyncosia minima. Low-level (0.7%) seed transmission of ZYMV was found in seedlings grown from seed collected from zucchini (Cucurbita pepo) fruit infected with isolate Cvn-1. Seed transmission was absent in >9500 pumpkin (C. maxima and C. moschata) seedlings from fruit infected with isolate Knx-1. Leaf samples from symptomatic cucurbit plants collected from fields in five cucurbit-growing areas in four Australian states were tested for the presence of ZYMV. When 42 complete coat protein (CP) nucleotide (nt) sequences from the new ZYMV isolates obtained were compared to those of 101 complete CP nt sequences from five other continents, phylogenetic analysis of the 143 ZYMV sequences revealed three distinct groups (A, B and C), with four subgroups in A (I-IV) and two in B (I-II). The new Australian sequences grouped according to collection location, fitting within A-I, A-II and B-II. The 16 new sequences from one isolated location in tropical northern Western Australia all grouped into subgroup B-II, which contained no other isolates. In contrast, the three sequences from the Northern Territory fitted into A-II with 94.6-99.0% nt identities with isolates from the United States, Iran, China and Japan. The 23 new sequences from the central west coast and two east coast locations all fitted into A-I, with 95.9-98.9% nt identities to sequences from Europe and Japan. These findings suggest that (i) there have been at least three separate ZYMV introductions into Australia and (ii) there are few changes to local isolate CP sequences following their establishment in remote growing areas. Isolates from A-I and B-II induced chlorotic symptoms in inoculated leaves of Chenopodium quinoa, but an isolate from A-II caused symptomless infection. One of three commercial ZYMV-specific antibodies did not detect all Australian isolates reliably by ELISA. A multiplex real-time PCR using dual-labelled probes was developed, which distinguished between Australian ZYMV isolates belonging to phylogenetic groups A-I, A-II and B-II.

Application of satellite precipitation data to analyse and model arbovirus activity in the tropics

BackgroundMurray Valley encephalitis virus (MVEV) is a mosquito-borne Flavivirus (Flaviviridae: Flavivirus) which is closely related to Japanese encephalitis virus, West Nile virus and St. Louis encephalitis virus. MVEV is enzootic in northern Australia and Papua New Guinea and epizootic in other parts of Australia. Activity of MVEV in Western Australia (WA) is monitored by detection of seroconversions in flocks of sentinel chickens at selected sample sites throughout WA.Rainfall is a major environmental factor influencing MVEV activity. Utilising data on rainfall and seroconversions, statistical relationships between MVEV occurrence and rainfall can be determined. These relationships can be used to predict MVEV activity which, in turn, provides the general public with important information about disease transmission risk. Since ground measurements of rainfall are sparse and irregularly distributed, especially in north WA where rainfall is spatially and temporally highly variable, alternative data sources such as remote sensing (RS) data represent an attractive alternative to ground measurements. However, a number of competing alternatives are available and careful evaluation is essential to determine the most appropriate product for a given problem.ResultsThe Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) 3B42 product was chosen from a range of RS rainfall products to develop rainfall-based predictor variables and build logistic regression models for the prediction of MVEV activity in the Kimberley and Pilbara regions of WA. Two models employing monthly time-lagged rainfall variables showed the strongest discriminatory ability of 0.74 and 0.80 as measured by the Receiver Operating Characteristics area under the curve (ROC AUC).ConclusionsTMPA data provide a state-of-the-art data source for the development of rainfall-based predictive models for Flavivirus activity in tropical WA. Compared to ground measurements these data have the advantage of being collected spatially regularly, irrespective of remoteness. We found that increases in monthly rainfall and monthly number of days above average rainfall increased the risk of MVEV activity in the Pilbara at a time-lag of two months. Increases in monthly rainfall and monthly number of days above average rainfall increased the risk of MVEV activity in the Kimberley at a lag of three months.

Seasonality, abundance and breeding biology of one of the largest populations of nesting flatback turtles, Natator depressus: Cape Domett, Western Australia

Cape Domett, located in tropical Western Australia, supports a significant population of flatback turtles, Natator depressus, but the magnitude of this was previously underestimated. We assessed temporal nesting abundance to find that Cape Domett supports one of the largest aggregated nesting flatback turtle populations globally with annual abundance in the order of several thousand individuals (estimated = 3250, 95% CI = 1431–7757). We assessed temporal abundance within a year to find turtles nested throughout the year with peak nesting occurring between August and September. This paper re-evaluates the importance of this major flatback turtle nesting site and shows the first detailed examination of flatback turtle nesting biology in north-western Australia.

Influence of latitude, water depth, dayv.night and wetv.dry periods on the species composition of reef fish communities in tropical Western Australia

Trap sampling over reefs in deep (mean = 20 m) and shallow (mean = 10 m) waters alongc. 1500 km of coastline in tropical north‐western Australia during both day and night and in wet and dry periods yielded 23 377 fishes, representing 32 families, 58 genera and 119 species. Individuals of the Serranidae, Lutjanidae, Lethrinidae and Carangidae contributed 88·9% to the total catch. The ichthyofaunal compositions of the Kimberley, Canning and Pilbara bioregions were relatively discrete. Species composition was influenced far more by location (latitude) than by water depth, period and time of day, and underwent a gradational change southwards. The latter change reflected differences in the trends exhibited by the relative abundances of certain species with increasing latitude and the confinement of other species largely to particular regions. The three most abundant species,i.e.Lethrinussp. 3,Lutjanus carponotatusandLethrinus laticaudiscontributed 34·8, 20·8 and 11·6% to the total catch, respectively. The first species was rarely recorded in the two most northern locations and was abundant in the four most southern locations, whereas the last two species were relatively more abundant in northern than in southern locations.Lutjanus bitaeniatusandLutjanus johniiwere found exclusively at the two locations in the Kimberley region, whereasAbalistes stellatus,Pentapodus emeryiiandLethrinus nebulosuswere not caught in this region but were found in both locations of the Canning and Pilbara regions. The species composition in deep and shallow waters at each location almost invariably differed significantly between day and night and between dry and wet periods, with species such asL. bitaeniatus,L. johnii,Lutjanus sebaeandA. stellatusbeing more abundant over deep reefs, whereasL. carponotatus,L. laticaudis,Siganus fuscescensandLethrinus lentjanwere more numerous over shallow reefs. Species such asL. johniiandLethrinus atkinsoniwere relatively more important in night‐time than daytime catches, whereas the reverse applied toLethrinus lentjan,L. laticaudisandChoerodon cyanodus.Lethrinussp. 3 andL. laticaudiswere relatively more important in catches during the dry than wet period.

The enigma of 3400 years BP coastal oolites in tropical northwest Western Australia… why then, why there?

Oolites crop out along the northwestern coast of Western Australia at Port Smith, about 80 km SW of Broome. An oolitic coastal ridge truncated by marine erosion exposes subtidal, intertidal, and supratidal (aeolian) facies. The deposits are firmly indurated and composed of about 75% tangentially and moderately thickly layered, aragonitic ooid grains with over 90% quartz nuclei. Subtidal sedimentary structures are exposed about a metre above the present high tide mark, hinting that sea level may have been somewhat higher when the shoreline was formed. However, the macrotidal range of up to 7 m, and the possibility of cyclonic surges along the coast, precludes unequivocal determinations on this point. Whole-rock amino acid racemisation (AAR) geochronology (epimerisation of isoleucine: d-alloisoleucine/ l-isoleucine or A/I) on each facies of the oolite outcrop averaged 0.106 ± 0.013 ( N = 10). The modern beach contains fewer ooids (∼ 30%), and nearly half of these are stained brown, grey, or black, perhaps as a result of burial, reduction and/or mineralization. A higher (older) mean and large standard deviation in whole-rock amino acid ratio of 0.145 ± 0.067 ( N = 2) supports our inference that ooids on the modern beach were reworked from fossil deposits. Reverse phase chronostratigraphy (RPC) on individual ooid grains holds tremendous promise in this preliminary study. RPC results show a narrow variation of d/ l values (CV = 6–11%), and yield nearly identical d/ l Asp means from light coloured fossil ooids (0.307 ± 0.018 ( N = 17)); light (0.323 ± 0.026 ( N = 12)) and dark coloured ooids (0.298 ± 0.027 ( N = 10)) from the active beach face. When compared to A/I ratios from 14C dated mid-Holocene ooids in the Bahamas, the mean A/I from Port Smith reflects an age of ca. 3500–4500 years that is in agreement with a calibrated AMS 14C age of 3370 ± 50 calendar years BP on the same material. Thus, the ooids were formed, transported, emplaced, strongly cemented, and largely eroded from the beach ridge in only 3400 years. The environmental conditions that underlie a pulse of ooid deposition during a brief period of the mid-Holocene almost certainly involve extensive tidal inlets in the area, a possible mid-Holocene oscillation 1–2 m above present, and a subsequent fall to present level that terminated the process. Apparently, a unique combination of factors produced ooids here, and in only a handful of other sites in Australia and the Indian Ocean.

Mapping Research Capacity in North-Western Tropical Australia

Research capacity in two jurisdictions in tropical northwestern Australia was mapped to a searchable website. The website provides ready access to all research organisations in the region with the underlying database providing a baseline against which developments in research and research networks can be measured. Of 202 research entities entered into the database, 38 were businesses, 12 civil society organisations, five cooperative research centres, 10 government research institutes, 64 government agencies within three jurisdictions and 70 university research groups within seven universities. The data were analysed by sector to describe the size and linkages between organisations, areas of research strength and socioeconomic objectives of research. Most enterprises undertaking research in tropical Western Australia and the Northern Territory are small with the majority having fewer than 10 research staff. The primary area of expertise for research entities in tropical Western Australia and the Northern Territory is agricultural and environmental research, which is also the area where there is greatest breadth of capacity. Similarly, the socioeconomic objective of most research entities is in fields related to environmental management and social development with the breadth of capacity greatest in environmental policy frameworks. There were substantial differences between the skills and direction of research in government and the universities and those in business.

Prospects for a restorative fishery enhancement of Lake Kununurra: a high-level tropical impoundment on the Ord River, Western Australia

The high-level irrigation water supply dams of the Ord River in tropical Western Australia impede the movement of Barramundi Lates cafcarifer and other tropical fish species. A recreational Barramundi fishery enhancement of Lake Kununurra using a fishway has been widely promoted as advancing fishery conservation and the reformation of land and water management practices within the greater Ord River region. Of the fishways considered here, none have been found to admit Barramundi in the numbers and size classes necessary to establish or maintain the recreational fishery. Reasons for this include an inadequate understanding of fish behaviour and/or fishway deSign faults. The seemingly reluctant use of fishways by Barramundi might also be confounded by some observations being made on rivers where Barramundi populations are either comparatively small or non-existent. The alternative to a fishway is hatchery stocking. This option, like a dedicated Barramundi fishway, represents a single-species approach to fishery enhancement and is the least legitimate attempt to restore the ecological integrity of the fish communities of either Lake Kununurra or the Ord River. We argue that progress toward the restoration of the lake should continue, though a fishery enhancement programme that incorporates the broader fish community and not just a single species, would better rebuild the presently degraded Ord River system. Of the available options, we recommend testing an experimental model that incorporates aspects of the vertical-slot and bypass fishway designs, with the objectives being to learn migratory fish behaviour, abundance, and patterns and cues for fish movement. This approach can incorporate Barramundi as the target species to better understand entrance design constraints, minimum slot widths for larger fish, and operation under low flows during peak irrigation water demands, but still accommodate the movement of tropical fishes during these periods.

Dynamics of the turbidity maximum in King Sound, tropical Western Australia

King Sound is a 100-km-long embayment located in tropical northwestern Australia with a spring tidal range of 11 m. This is the second largest tide in the world after the Bay of Fundy in Canada. Intertidal areas cover about 800 km 2. The upper reaches of the sound are turbid with fine suspended sediment concentration reaching 3 kg m −3. Field studies of the dynamics of water and fine sediment were carried out in the dry seasons of 1997 and 1998. The tide was a propagating wave, shoaling and dissipating by friction as it entered the sound. This mode of propagation generated an asymmetric tidal current with a stronger current at flood than at ebb. An evaporation-driven salinity maximum zone was found in the upper reaches of the sound, and this was also where the turbidity maximum occurred. Tidal pumping by the tidal asymmetry and, possibly, the biological filter formed by muddy marine snow, trapped the fine sediment in the upper regions of King Sound. Wind-driven waves contributed significantly to entrainment of bottom fine sediment, possibly through wave pumping of the sediment and not wave-induced orbital velocities. Field data suggest that erosion of bottom fine sediment was proportional to the sixth power of the tidal current and the third power of the wave height.

Link between reproductive output and larval supply of a common damselfish species, with evidence of replenishment from outside the local population

The link between reproductive output and larval supply is described for a common dam- selfish species Pomacentrus vaiuli in tropical Western Australia. I monitored the reproduction of 2 groups of P. vaiuli that occupied slightly different habitats. Egg clutches laid on artificial substratum were quantified on a bi-weekly basis during the consecutive spawning seasons of 1994/95 and 1995/96. The timing of egg production was similar for both groups and showed a distinctly semi-lunar pattern. The majority of the larvae hatched during the period when flood tide occurred 2 h either side of sunset. At Ningaloo this only happens during neap tides when the tidal amplitude is at its mini- mum. However, this means that larvae are dispersed nocturnally when the risk of predation is mini- mal. No relationship was found between egg production and changes in water temperature. Spawn- ing ended prematurely for 1 of these groups of fish following the passing of a tropical cyclone within 80 km of the coast. Larval supply of P. vaiuli was estimated in the vicinity of the reproductive sites by capturing pre-settlement fish at one of these locations (Tantabiddy), and post-settlement fish at the other (Bundegi). The arrival of P. vaiuli larvae to Tantabiddy was on a lunar cycle with periodicities between 28 to 30 d. When these larval supply data were lagged by the average pelagic duration of 22 d, and then cross-correlated with the spawning data, there was a weak relationship. At Bundegi, I constructed recruitment patterns and estimated the birth dates of juveniles, using otolith analysis. By back-calculating the birth dates of individual fish that settled at Bundegi I made 2 discoveries. Firstly, most juveniles from 1994/95 hatched when spawning output at Bundegi was low, and secondly, more than 50% of fish caught in 1995/96 hatched after the spawning season had ended prematurely. This suggests that many of the juvenile P. vaiuli that settled at Bundegi during the sec- ond summer were not produced by this population but from elsewhere. I discuss the likelihood that larvae arriving to Ningaloo are from adult populations which inhabit fringing reefs to the north and that the observed patterns in larval supply are the result of an interaction between both physical and behavioural processes.