Water intakes entrain large numbers of fish larvae in waterways where drift coincides with large-scale extraction. While modern fish-protection screens can reduce these losses, many are not designed for larvae and were developed or evaluated primarily for juveniles and adults. This study evaluated the effectiveness of Australia's fish screen design criteria (which specify a maximum approach velocity of 0.1 m s-¹ and slot widths of 2-3 mm) for protecting drifting larval Murray cod (Maccullochella peelii). Larvae were tested in a large flume under combinations of approach velocity (0.1 or 0.2 m s-¹), slot width (2 or 3 mm), and proximity. Entrainment rose sharply with velocity; slot size had a smaller interactive effect. The most protective combination (0.1 m s-¹ and 2 mm) reduced entrainment by up to 94% relative to unscreened conditions. Three-dimensional flow measurements helped explain how velocity vectors interact to influence larval fate. The results demonstrate that Australia's current standards, although developed for juveniles, can provide strong larval protection when strictly followed, but that even modest departures can sharply increase risk. More broadly, since the criteria tested here are less conservative than those adopted in many other countries, where empirical evidence on larval behaviour does not exist, targeted research could determine whether existing guidelines warrant revision.

Context Entrainment and removal of fish from aquatic ecosystems can occur at water pump offtakes. Exclusion screens that reduce these impacts are recognised as an important conservation measure. Aims Evaluate the effectiveness of the Australian screen design guidelines in protecting larvae and young-of-year age class of a native fish species, Murray cod Maccullochella peelii. Methods Entrainment and impingement of postflexion larvae and young-of-year were assessed in a controlled laboratory environment. Tests were conducted under a range of approach velocities (AV) and impingement durations for two screen materials. Key results Fish screens reduced larval entrainment by ≤84%. Screens had no significant effect on reducing larval entrainment at AV ≥0.125 m s−1. Impingement of young-of-year was positively associated with AV and mortality increased with impingement duration, irrespective of screen type. Conclusions To protect early life-stage Murray cod, it is recommended that water pump offtakes be fitted with 2-mm vertical wedge-wire stainless steel screens and AV be limited to ≤0.1 m s−1. Implications This study represents the first assessment of the effectiveness of the Australian screen design guidelines in protecting larvae, providing knowledge to further refine specifications for screen design and support the recovery of native fish populations.

Context. Modern fish-protection screens are being implemented globally to conserve aquatic ecosystems and protect water infrastructure. Australian governments have invested similar to A$40 x 10(6) towards incentive programs. However, evaluation remains limited. Aims. This study aimed to review progress, summarise research, and identify future priorities for screening in Australia. Methods. The study analysed screen installations to date, estimating their benefits for native fish and agricultural water supply. Key results. In New South Wales, 36 pumped water diversions were screened from 2018 to 2024. These installations protect over 819,000 native fish annually and can deliver up to 2600 ML of cleaner water per day, servicing over 230 km(2) of irrigated agriculture. By 2026, these figures are set to rise to 48 sites, 1.72 x 10(6) native fish year(-1) and 5461 ML day(-1) of water. Conclusions. Although incentive programs are generating substantial public benefits, valued at least A$177 ML-1 of water passing through a modern screen, and with benefit-cost ratios averaging 4:1, installation costs remain high and national progress has been limited.

Modern fish-protection screens offer significant potential benefits for Australia. The Commonwealth and New South Wales (NSW) governments have invested over $30m to incentivise early adoption by water users. However, successful adoption requires an understanding of the motivations and abilities of water users, and strategies to overcome key barriers to adoption. Four practices have been used by the NSW Government to strengthen understanding of stakeholders and encourage participation in incentive programs by water users. These are: applying social learning concepts to screening programs; evaluating stakeholder needs; identifying and mapping stakeholders and their relationships; and, integrating science in communication and engagement. Analysing the motivations and abilities of water users revealed three key motivations: to save money, to protect fish, and to improve their reputation or social licence to operate. However, the ability of water users to install a fish-protection screen was found to vary significantly. A range of barriers have been identified by water users in NSW, and solutions or strategies developed to address each one. Today, in Australia, over 2,000 ML/day of water is being delivered through modern fish-protection screens, protecting ~580,000 native fish annually at 31 sites across NSW, Victoria and Queensland (60% being in NSW). Existing investment may see these numbers increase to ~7,000 ML/day and ~2 million native fish/yr by June 2024. The application of the methods to understand and strategically engage with stakeholders should enable improved uptake of screening technologies in other jurisdictions and areas of conservation concern into the future.

Mass fish kills capture the world’s attention and their frequency is increasing worldwide. The sudden death of many millions of native fish in the Darling–Baaka River in Australia in 2018–19 was a catalyst for the 11 articles in this special issue. Collectively, they advance our understanding of how to manage these events, dealing with: ecological impacts and recovery; technologies and approaches for prediction, preparedness and response; and the role of the public in preparing and responding to these catastrophic events.

Vegetated coastal wetlands, including seagrass, saltmarsh and mangroves, are threatened globally, yet the need to avert these losses is poorly recognized in international policy, such as in the Convention on Biological Diversity and the United Nations (UN) Sustainable Development Goals. Identifying the impact of overlooking coastal wetlands in ecosystem assessment frameworks could help prioritize research efforts to fill these gaps. Here, we examine gaps in the recognition of coastal wetlands in globally applicable ecosystem assessments. We address both shortfalls in assessment frameworks when it comes to assessing wetlands, and gaps in data that limit widespread application of assessments. We examine five assessment frameworks that track fisheries, greenhouse gas emissions, ecosystem threats, and ecosystem services. We found that these assessments inform management decisions, but that the functions provided by coastal wetlands are incompletely represented. Most frameworks had sufficient complexity to measure wetland status, but limitations in data meant they were incompletely informed about wetland functions and services. Incomplete representation of coastal wetlands may lead to them being overlooked by research and management. Improving the coverage of coastal wetlands in ecosystem assessments requires improving global scale mapping of wetland trends, developing global-scale indicators of wetland function and synthesis to quantitatively link animal population dynamics to wetland trends. Filling these gaps will help ensure coastal wetland conservation is properly informed to manage them for the outstanding benefits they bring humanity.

SummaryThe diversion of water from rivers removes millions of fish from Australian waterways each year. Modern diversion screens are available that can reduce fish losses by 90% and stop debris entering irrigation systems. Uptake of this technology in the United States has protected fish and infrastructure. However, application in Australia has been poor and both the problem and its solution continue to be overlooked. To address this, we summarise multiple lines of evidence of fish losses in Australia and propose a way forward. Large losses of fish at diversions have been reported for close to a century, providing compelling evidence of population‐scale impacts on native fish. We discuss the solution, outlining the progress being made to bring modern screening technology to Australia, including a social learning framework to improve how water is diverted and focussing on collaboration between the fisheries, agriculture and engineering sectors, and underpinned by science. We conclude that uptake of modern screens will rely on dialogue moving past whether a problem or solution exists, to the following: how screening can be better integrated with water and environmental management; where investment should be prioritised; and how screening could be funded. If Australia gets this right, substantial benefits can be realised, saving millions of native fish every year, bolstering native fish recovery programmes, reducing ongoing costs for water users and enhancing the economic and social value in regional areas by boosting manufacturing, service industries, tourism and recreational fisheries.

Global-scale conservation initiatives and policy instruments rely on ecosystem indicators to track progress towards targets and objectives. A deeper understanding of indicator interrelationships would benefit these efforts and help characterize ecosystem status. We study interrelationships among 34 indicators for mangroves, saltmarsh, and seagrass ecosystems, and develop data-driven, spatially explicit typologies of coastal wetland status at a global scale. After accounting for environmental covariates and gap-filling missing data, we obtained two levels of clustering at 5 and 18 typologies, providing outputs at different scales for different end users. We generated 2,845 cells (1° (lat) × 1° (long)) globally, of which 29.7% were characterized by high land- and marine-based impacts and a high proportion of threatened species, 13.5% by high climate-based impacts, and 9.6% were refuges with lower impacts, high fish density and a low proportion of threatened species. We identify instances where specific actions could have positive outcomes for coastal wetlands across regions facing similar issues. For example, land- and marine-based threats to coastal wetlands were associated with ecological structure and function indicators, suggesting that reducing these threats may reduce habitat degradation and threats to species persistence. However, several interdimensional relationships might be affected by temporal or spatial mismatches in data. Weak relationships mean that global biodiversity maps that categorize areas by single indicators (such as threats or trends in habitat size) may not be representative of changes in other indicators (e.g., ecosystem function). By simplifying the complex global mosaic of coastal wetland status and identifying regions with similar issues that could benefit from knowledge exchange across national boundaries, we help set the scene for globally and regionally coordinated conservation.

Recent environmental flow management in the Murray–Darling basin, south‐eastern Australia, has centred on restoring natural flooding regimes to meet ecological requirements, including the promotion of native fish recruitment, despite uncertainty about the effectiveness of managed environmental flooding. This study investigated recruitment responses of small‐bodied native and non‐native fish species to a large natural flood, supported by managed environmental flows in the Macquarie Marshes of the Murray–Darling basin. We surveyed the fish community within the heavily regulated, dryland floodplain system of the marshes, the year after breaking of the Millennium drought (2002–2009). During the spring–summer of 2010, the Macquarie Marshes experienced a one‐in‐10‐year flood, sustained by two environmental flow allocations, flooding 174,000 ha of floodplain. Five native species were collected across the nine study sites. Two non‐native species were particularly abundant during the flood, outnumbering the five native species in a ratio of 32:1, with Gambusia holbrooki the most abundant species, comprising 87% of all native and non‐native individuals captured. There was no marked effect of flood stage on the total abundance of small‐bodied native or non‐native fishes, but the composition of the fish community varied between surveys of the rising and falling phases of the flood. We did not capture any larval or post‐larval fish despite using a variety of suitable sampling methods. The lack of larvae in the Macquarie Marshes, following extensive flooding, most likely reflected the overall poor condition of native fish communities and low standing stocks of mature fish, resulting from deleterious long‐term effects of flow regulation exacerbated by drought. A gradual rebuilding of ecosystem health, fish health, and resilient fish populations by active management of environmental flows to impose more natural boom and bust dynamics may be needed to restore fish reproduction and recruitment in this regulated river.

Food web subsidies from external sources (“allochthony”) can support rich biological diversity and high secondary and tertiary production in aquatic systems, even those with low rates of primary production. However, animals vary in their degree of dependence on these subsidies. We examined dietary sources for aquatic animals restricted to refugial habitats (waterholes) during the dry season in Australia’s wet–dry tropics, and show that allochthony is strongly size dependent. While small-bodied fishes and invertebrates derived a large proportion of their diet from autochthonous sources within the waterhole (phytoplankton, periphyton, or macrophytes), larger animals, including predatory fishes and crocodiles, demonstrated allochthony from seasonally inundated floodplains, coastal zones or the surrounding savanna. Autochthony declined roughly 10% for each order of magnitude increase in body size. The largest animals in the food web, estuarine crocodiles (Crocodylus porosus), derived ~80% of their diet from allochthonous sources. Allochthony enables crocodiles and large predatory fish to achieve high biomass, countering empirically derived expectations for negative density vs. body size relationships. These results highlight the strong degree of connectivity that exists between rivers and their floodplains in systems largely unaffected by river regulation or dams and levees, and how large iconic predators could be disproportionately affected by these human activities.

Rivers and wetland ecosystems are degraded by diversions of water upstream. In response, governments have reallocated water to flood wetlands, mimicking natural inundation of habitats known to drive booms in native freshwater fish production. Individual flow events allow the ecological outcomes of restoration efforts to be evaluated, in order to improve ongoing adaptive management. This study investigated the population size and recruitment responses of seven native and three alien fish species to widespread floodplain inundation at 15 sites across the Macquarie Marshes, a regulated wetland in Australia's Murray-Darling Basin. Flooding during the late winter, when water temperatures were 4 to 12.6 degrees C below the spawning threshold for native fish species present in the system, promoted reproduction and recruitment by alien species, which were significantly more abundant than native species after flooding. Fish assemblage structure also differed significantly between main channel and floodplain habitats, with macrophytes, pH, emergent vegetation, flow velocity and small wood debris accounting for 59% of spatiotemporal variation in fish assemblage structure. Strong correlations were identified between the length of spawning window and post-flood abundance of young-of-year and recruit size classes in the most abundant alien and native fish species. Future environmental flows, particularly those that inundate floodplain habitats, need to be delivered in light of the confounding effects of flow-temperature coupling and the lower spawning temperature thresholds of alien species. Copyright (c) 2014 John Wiley & Sons, Ltd.

[Extract] The amphibian disease chytridiomycosis, caused by the pathogen Batrachochytrium dendrobatidis (Bd), has dramatically affected amphibians, causing population declines in over 200 species worldwide (Fisher et al. 2009). The disease is widespread, driving amphibian declines in North America (Muths et al. 2003; Briggs et al. 2005), Australia (Berger et al. 1998), Central America (Lips et al. 2006) and South America (Catenazzi et al. 2011). The variation in susceptibility to disease and mortality seen among host species, populations and locations is at least partially driven by interplay between external environmental and internal host-specific factors (Woodhams et al. 2007; Searle et al. 2011; Blaustein et al. 2012). While at a single location some species may be locally extirpated, others may persist (Lips et al. 2006). Amphibian infection prevalence and mortality rates due to chytridiomycosis are correlated with ambient environmental conditions: being highest during cooler months and at higher elevations (Berger et al. 1998; Woodhams and Alford 2005; Kriger and Hero 2008).

Freshwater environments and their fishes are particularly vulnerable to climate change because the persistence and quality of aquatic habitat depend heavily on climatic and hydrologic regimes. In Australia, projections indicate that the rate and magnitude of climate change will vary across the continent. We review the likely effects of these changes on Australian freshwater fishes across geographic regions encompassing a diversity of habitats and climatic variability. Commonalities in the predicted implications of climate change on fish included habitat loss and fragmentation, surpassing of physiological tolerances and spread of alien species. Existing anthropogenic stressors in more developed regions are likely to compound these impacts because of the already reduced resilience of fish assemblages. Many Australian freshwater fish species are adapted to variable or unpredictable flow conditions and, in some cases, this evolutionary history may confer resistance or resilience to the impacts of climate change. However, the rate and magnitude of projected change will outpace the adaptive capacities of many species. Climate change therefore seriously threatens the persistence of many of Australia’s freshwater fish species, especially of those with limited ranges or specific habitat requirements, or of those that are already occurring close to physiological tolerance limits. Human responses to climate change should be proactive and focus on maintaining population resilience through the protection of habitat, mitigation of current anthropogenic stressors, adequate planning and provisioning of environmental flows and the consideration of more interventionist options such as managed translocations.

Background: Given the globally poor protection of fresh waters for their intrinsic ecological values, assessments are needed to determine how well fresh waters and supported fish species are incidentally protected within existing terrestrial protected-area networks, and to identify their vulnerability to human-induced disturbances. To date, gaps in data have severely constrained any attempt to explore the representation of fresh waters in tropical regions.Methodology and Results: We determined the distribution of fresh waters and fish diversity in the Wet Tropics of Queensland, Australia. We then used distribution data of fresh waters, fish species, human-induced disturbances, and the terrestrial protected-area network to assess the effectiveness of terrestrial protected areas for fresh waters and fish species. We also identified human-induced disturbances likely to influence the effectiveness of freshwater protection and evaluated the vulnerability of fresh waters to these disturbances within and outside protected areas. The representation of fresh waters and fish species in the protected areas of the Wet Tropics is poor: 83% of stream types defined by order, 75% of wetland types, and 89% of fish species have less than 20% of their total Wet Tropics length, area or distribution completely within IUCN category II protected areas. Numerous disturbances affect fresh waters both within and outside of protected areas despite the high level of protection afforded to terrestrial areas in the Wet Tropics (>60% of the region). High-order streams and associated wetlands are influenced by the greatest number of human-induced disturbances and are also the least protected. Thirty-two percent of stream length upstream of protected areas has at least one human-induced disturbance present.Conclusions/Significance: We demonstrate the need for greater consideration of explicit protection and off-reserve management for fresh waters and supported biodiversity by showing that, even in a region where terrestrial protection is high, it does not adequately capture fresh waters.

In Australia’s Wet Tropics rivers, perennial base flows punctuated by wet season floods drive instream responses across a range of spatial and temporal scales. We combined gut-content and stable-isotope analyses to produce preliminary webs depicting trophic links between fish, their main prey items and basal productivity sources. We then used these webs to test the applicability of general food web principles developed in other tropical systems. Although a range of sources appeared to underpin fish productivity, a large portion of total energy transfer occurred through a subset of trophic links. Variability in food web structure was negatively correlated with spatial scale, being seasonally stable at river reaches and variable at smaller scales. Wet Tropics rivers are similar to those in other tropical areas, but exhibit some unique characteristics. Their high degree of channel incision improves longitudinal connectivity, thereby allowing fish to move between mesohabitats and target their preferred prey items, rather than shifting their diet as resources fluctuate. However, this also inhibits lateral connectivity and limits terrestrial energy inputs from beyond the littoral zone.

Wet-season flooding causes dietary shifts in tropical freshwater fish by regulating instream productivity, habitat structure and food availability. These dynamics have been comprehensively documented worldwide, but data are limited for Australia’s Wet Tropics rivers. The aim of the present study was to extend our earlier fish–habitat model for these systems by examining the role of trophic dynamics in determining fish assemblage composition. Chlorophyll a and phaeophytin concentrations, benthic and littoral invertebrates and fish were collected at four sites in the lower Mulgrave River under a range of flow conditions. Wet-season flooding caused significant reductions in instream productivity, whereas habitat disturbance reduced densities and abundances of littoral and benthic invertebrates. However, volumetric gut contents of 1360 fish, from 36 species, revealed seasonal shifts in guild membership by only two species, with fish moving between sites to target their preferred prey items – largely irrespective of differences in habitat structure. As a result, the food consumed by the fish community present at each site closely reflected the seasonal availability of food resources. The present paper questions whether fish community composition in small tropical rivers can be accurately predicted from habitat surrogates alone and encourages consideration of constraints imposed by the trophic dynamics and reproductive ecology of fish.

Fish in arid‐zone rivers are dependent on waterholes for refuge during drought. In heavily regulated systems, water extraction for human use has the potential to exacerbate drought conditions and increase the reliance of fish on refugia. This study investigated this hypothesis by surveying fish communities at 25 sites in the Ramsar listed Macquarie Marshes, before and after a 23‐GL environmental flow event. Although such flows are central to restoration efforts in the Murray‐Darling Basin, limited water availability often forces water managers to make difficult triage decisions regarding which ecological assets to service. This study aimed to provide an update on the current health and status of native fish populations in the Macquarie Marshes and discuss how small flows may best be delivered to meet their ecological needs, particularly during droughts. Eight native species were collected, but they were outnumbered by three alien species by more than 3:1. Post‐flooding recruitment was observed in most species and mean species richness of sampling sites increased significantly, as fish moved out of drought refugia to utilize a more diverse array of microhabitats. This study presents a conceptual model of fish use of refugia and recommends that key low‐flow refugia be targeted for remediation efforts. Copyright © 2009 John Wiley & Sons, Ltd.

Strong relationships between seasonal flooding, instream habitat structure and fish assemblages have been well documented in large tropical rivers (e.g. the flood pulse concept). However, the mechanics of these relationships are likely to differ substantially in smaller coastal rivers, such as those in Costa Rica, south-east Brazil and Australia’s Wet Tropics. These systems typically feature steep upland streams with short, deeply incised lowland channels and poorly connected floodplains. This hypothesis was investigated by documenting spatial and temporal variation in fish-habitat relationships in the Mulgrave River, north-east Queensland. Sampling was conducted at four lowland sites under a range of flow conditions, from dry-season baseflows to a one-in-ten-year flood. Longitudinal environmental gradients and fine-scale habitat patches were important in regulating fish assemblage structure during the dry season. However, high wet-season flows, constrained by the deep channel, acted as disturbances rather than gentle flood-pulses. In particular, the mobilisation of bed sediments led to scouring of aquatic vegetation and a dramatic reduction in habitat heterogeneity. Seasonal movements of fish led to significant changes in assemblage structure – from a community dominated by Neosilurus ater, Hypseleotris compressa, Awaous acritosus and Redigobius bikolanus during the dry season, to one dominated by Nematalosa erebi, Ambassis agrammus and Glossamia aprion during the wet season. Based on these observations, together with information from the literature, a conceptual model of fish-habitat dynamics is presented that is better suited to small tropical rivers than those developed in larger systems with expansive floodplains.