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La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.Knowledge of the biology of native fishes of the Murray-Darling Basin is based largely on studies conducted under hatchery conditions and on a limited number of recreationally important species. From observations that increases in water level in aquaculture ponds initiate spawning in some species, and from limited studies of wild fishes and studies in overseas floodplain river systems, a perception has emerged of the importance of flooding and the flood plain in the life cycles of Murray-Darling fishes in general. However, there is little confirmatory evidence of the use of temporary floodplain habitats by larvae, juveniles or adults. The significance of in-channel habitats, especially for rearing, has received little attention. Murray-Darling fish species can be placed into three life history modes, based mainly on spawning style and time and developmental intervals of larvae at first feeding. Fish in each group may be able to take advantage of floods if the timing is right and prey are plentiful, however, the larvae of some species are able to recruit under non-flood conditions within the main river channel. This forms the basis of the low flow recruitment hypothesis, which attempts to explain why some species spawn during the warmest months and lowest flows and how they are able to recruit under these conditions. This hypothesis is then placed in the context of the current state of knowledge of the relationships between flow and the biology of Murray-Darling fishes, specifically cues for spawning, movement and recruitment. The lack of widespread evidence for floodplain use by any life history interval of fish may be due to a paucity of study, however, there are some fundamental factors, such as the predictability of timing and duration of high flow events as well as the lack of coincidence of high flows and high temperatures in some regions of the Basin, which may be important in determining the use of floodplain habitats by fish.

MDFRC item.1. One of the greatest threats to lotic ecosystems is flow regulation. The impacts of flow regulation on native fish are often mitigated using periodic water allocations, termed environmental flows. The effectiveness of environmental flows has been studied in some systems, but the role of flow conditions prior to water allocation (i.e. antecedent conditions) has rarely been quantified. 2. We evaluated the effects of floodplain inundation due to variable river flows on fish abundance in wetlands of the mid-Murray River, Australia, using a hierarchical multi-species model parameterized to estimate fish abundance while accounting for variable detection. We evaluated the effects of antecedent conditions on three time-scales, including patterns in long-term (5 years prior), medium-term (1 year prior) and short-term (3 months prior) wetland inundations. 3. While species-specific responses to antecedent conditions varied, we found a general divergence in the responses of native and non-native species. Native fish tended to respond positively to consistent frequent inundation of wetlands, while non-native fish tended to respond positively to long- or medium-term dry periods and short-term wet periods. 4. Fish detection probability varied among species, sampling gears, wetland areas and wetlands, indicating that accounting for variable detection can be critical when evaluating patterns in fish abundance. 5. Synthesis and applications. We found that antecedent conditions can be important for determining environmental water allocation policies. Our results indicated that native fish generally responded positively to frequent inundation of wetlands, while non-native species generally responded positively to long dry periods followed by short-term inundation events. For some non-native species, long dry periods not only generated a positive response in abundance, but enhanced the positive response to short-term inundation events. The divergence between native and non-native fishes' responses to antecedent conditions provides opportunities for managers to allocate water to favour native fish assemblages. Future research of environmental flows for managing fish assemblages should consider antecedent conditions and apply models that account for incomplete detection, such as the one developed here, to better inform the management process.

MDFRC item.1. Flow alteration has reduced connectivity between many of the world’s rivers and their floodplains,causing changes in riverine productivity and the isolation of floodplain wetlands. Environmental water is being increasingly used to help restore wetland habitats and their biota, including fish. However, some of these managed deliveries of water occur into discrete wetlands via artificial structures or at unseasonal times and may not deliver the expected gains in fish production. 2. In the Murray River, south-eastern Australia, we examined the relationship between attributes of watering and fish production (species-specific recruitment, total abundance), at two time intervals:short term (6–8 weeks after watering) and at the end of the spawning season (April) for 26 discrete watering events. The study also recognised the importance of habitat in mediating fish responses to watering and examined whether fish abundance after environmental water delivery is better predicted by attributes of watering or wetland characteristics? 3. We found that attributes of watering, including water source, its method of delivery and timing, best described fish recruitment (0+ abundance) and total fish abundance. Managers of environmental water may be able to optimise fish recruitment and abundance if they source their water from the river and deliver it during the spawning period of the target species via means that facilitate fish passage.

Fish kills are very visible, with high levels of public scrutiny and major effects on populations. In 2018–19, extensive fish kills in the lower Darling River, south-eastern Australia, resulted in the deaths of millions of fish, including threatened and popular, iconic angling and important cultural species. This distressed local communities and the broader Australian society, who questioned the competence of fish and water management. Fish kills are increasing in frequency and severity, exacerbated by climate change. This paper reports on eight major fish-kill case studies across the Murray–Darling Basin that were examined to assess management adequacy. Field assessments and reporting have been poor, not documenting all species or numbers affected. Few values of fishes (cultural, conservation, recreational, social, ecological, economic) have been assessed and replacement or management costs not determined. There is a need to philosophically change our approach to take fish kills more seriously. More comprehensive approaches to assessment, evaluation and management are needed. Responsibilities for fish kills should be clarified and include water and habitat management agencies. Post-kill recovery plans that include the replacement of lost ecological assets should be published and enacted. This paper provides a fresh perspective on fish kills, with 15 key recommendations applicable to improve future management worldwide.

In the summer of 2018–19 mass fish kills occurred in the Lower Darling (Baaka) River in south-eastern Australia. The fish kills received national and international attention and have been the focus of numerous government agency and independent assessments. Although fish kills have previously been recorded in the Lower Darling region, the size and rapid succession of the 2018–19 ‘Menindee’ fish kills made them unprecedented in the Murray–Darling Basin, placing significant pressure on the native fish community. Although the deaths of millions of fish were documented, the significant negative effect that the fish kills had on local communities, particularly the traditional Baakandji people, was largely ignored. The social and cultural aspects of such events can have major non-economic effects on local communities. In this paper we document heart-felt feelings conveyed by local community members. Their sense of loss, despair and helplessness is compounded by frustration regarding water management and policy decision making in the Murray–Darling Basin. However, these tragic events have increased understanding of traditional Baakandji connection to the river and its fish and, together with local recovery efforts, now provide prospects for enhanced community and agency cooperation to improve the health of the lower Darling Baaka River and restore its native fish populations.

Directional or stabilising selection should drive the expression of a dominant movement phenotype within a population. Widespread persistence of multiple movement phenotypes within wild populations, however, suggests that individuals that move (movers) and those that do not (residents) can have commensurate performance. The costs and benefits of mover and resident phenotypes remain poorly understood. Here, we explored how the presence and timing of movements are correlated with annual somatic growth rates, a useful proxy for performance because it is easily measured and rapidly reflects environmental changes. We used otolith growth measurements and stable isotope analyses to recreate growth and among-reach movement histories of a partially migrating, long-lived freshwater fish, golden perch Macquaria ambigua. We compared the association between movement and growth at two temporal scales: (a) short-term (annual) differences in growth, in the years preceding, during or following movement; and (b) long-term (lifetime) differences in growth. Overall, 59% of individuals performed at least one among-reach movement, with these individuals subsequently more likely to move repeatedly throughout their lives. Movers grew faster than residents, with this difference most pronounced in the juvenile and early adult stages, when most movements occurred. Annual growth did not, however, change immediately prior to or following a specific movement event. Among-individual variation in growth was initially higher for residents than for movers but decreased with age, at a faster rate for residents than for movers, such that levels conformed after 5 years of age. Our results indicate that lifetime movement is linked to faster growth in the early years of a fish's life. These faster growing movers are likely to be larger at a given age, leading to numerous potential benefits. However, the persistence of resident phenotypes suggests that there is likely a cost-benefit trade-off to moving. The presence of multiple movement phenotypes may contribute to the resilience of populations by buffering against naturally and anthropogenically exacerbated environmental variability.

Inland fisheries make substantial contributions to food security and livelihoods locally, regionally, and globally but their conservation and management have been largely overlooked by policy makers. In an effort to remedy this limited recognition, a cross-sectoral community of scientists, practitioners, and policy makers from around the world convened a high-level meeting in 2015 at the Food and Agriculture Organization of the United Nations headquarters in Rome, Italy to develop recommendations for sustainable inland fisheries management. This meeting resulted in the production of the Rome Declaration, outlining ten key steps needed to achieve responsible inland fisheries. When the Ten Steps were conceived, they were framed in a global context because inland fisheries around the world face similar challenges, and it was hoped that these large-scale and ambitious steps would draw the attention of regional or international bodies for greater investment in their proper management. Most inland fisheries, however, are managed at a local (often community, watershed, or waterbody) scale with the "on-the-ground" practitioners, managers, assessment biologists, and stewardship officers responsible for achieving the promise of the Ten Steps. Here, we reflect on the relevance of the Ten Steps to practitioners using six regional case studies from around the globe (North America, South America, Europe, Asia, Australia, and Africa) to identify the extent to which existing efforts align with the Ten Steps and where there are opportunities to do more. Learning what is effective from local/regional actions should better inform a more global "action plan" and provide tangible guidance for implementation recognizing that global guidance needs to be informed by and acted upon by local practitioners. We conclude by considering the common challenges, synergies, and other emergent properties that arise from these case studies, and use these as a path forward to advancing responsible management of inland fisheries through the Rome Declaration. Of particular importance is the need to balance the high-level aspirational goals of the Ten Steps with the local cultural, socio-economic, and institutional realities that ultimately influence how humans interact with fisheries resources and aquatic ecosystems. This assessment provides valuable information on how to refine and implement the Ten Steps recognizing that success will require coordinated efforts among on-the-ground practitioners, scientists, stakeholders, rightsholders and international decision makers. Natural Sciences and Engineering Research Council of Canada; Genome Canada; Fonds de recherche du Quebec -Nature et Technologies grant from the Government of Quebec, Canada; Danish Rod and Net Fishing License Funds Published version Natural Sciences and Engineering Research Council of Canada(Natural Sciences and Engineering Research Council of Canada (NSERC)CGIAR); Genome Canada(Genome Canada); Fonds de recherche du Quebec -Nature et Technologies grant from the Government of Quebec, Canada; Danish Rod and Net Fishing License Funds Public domain – authored by a U.S. government employee

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.

Globally, river degradation has decimated freshwater fish populations. To help reverse this trend in a southeastern Australia river, we used multiple restoration actions, including reintroduction of instream woody habitat, riparian revegetation, removal of a weir hindering fish movement, fencing out livestock, and controlling riparian weeds. We monitored the responses of native fish at the segment scale (20 km) and reach scale (0.3 km) over 7 years to assess the effectiveness of the different restoration strategies. Two closely related species, Murray cod Maccullochella peeli and trout cod Maccullochella macquariensis, increased at the restored segment compared with the control segment. However, inherent differences between river segments and low sample size hampered assessment of the mechanisms responsible for segment‐scale changes in fish abundance. In contrast, at the reach scale, only M. peeli abundance significantly increased in reaches supplemented with wood. These differential responses by 2 closely related fish species likely reflect species‐specific responses to increased habitat availability and enhanced longitudinal connectivity when the weir improved passage around a fishway. Changes in M. peeli abundance in segments supplemented with and without wood suggest an increase in carrying capacity and not simply a redistribution of individuals within the segment, facilitated the observed expansion. Our findings confirm the need to consider individual fish species' habitat preferences carefully when designing restoration interventions. Further, species‐specific responses to restoration actions provide waterway managers with precise strategies to target fish species for recovery and the potential to predict fish outcomes based on ecological preferences.

The biomass of organisms of different sizes is increasingly being used to explore macroscale variation in food-web and community structure. Here we examine how invasive species and river flow regulation affect native fish biomass and fish community log10biomass – body mass scaling relationships in Australia’s largest river system, the Murray–Darling. The log10biomass – body mass scaling exponent (scaling B) of invasive fishes (95% CI: −0.14 to −0.18) was less negative than for native fishes (95% CI: −0.20 to −0.25), meaning that invasive species attained a higher biomass in larger size-classes compared to native species. Flow alteration and invasive common carp (Cyprinus carpio) biomass were correlated with severe reductions in native fish biomass ranging from −47% to −68% (95% CI). Our study provides novel evidence suggesting that invasive and native communities have different biomass – body mass scaling patterns, which likely depend on differences in their trophic ecology and body size distributions. Our results suggest that restoration efforts using environmental flows and common carp control has potential to boost native fish biomass to more than double the current level.

Recognition that many species share key life-history strategies has enabled predictions of responses to habitat degradation or rehabilitation by these species groups. While such responses have been well documented for freshwater fish that exhibit 'periodic' and 'opportunistic' life-history strategies, this is rare for 'equilibrium' life-history, due largely to their longevity and by comparison, more regular and stable levels of recruitment. Unfortunately, this limits the confidence in using life-history strategies to refine water management interventions to rectify the negative impacts of river regulation for these species. We addressed this knowledge gap for Murray cod Maccullochella peelii, a high-profile, long-lived recreationally popular equilibrium species in south-eastern Australia. We used monitoring data collected across a gradient of hydrologically altered rivers over two decades, to test various hypotheses linking recruitment strength with key attributes of the flow regime. Although Murray cod recruited in most years, as expected for an equilibrium species, responses to flow varied among and within rivers among years. We found links between recruitment strength and the magnitude and variation in discharge during the spring spawning period, as well as flows experienced by juvenile fish during summer and winter - the hydrological components most affected by river regulation. However, the specific slopes and directions of some of these links varied idiosyncratically across rivers. Our results emphasise the importance of accounting for flows that influence each of the key life stages during the recruitment process and lend support for managing rivers in accordance with the natural flow regime. It also shows the need for waterway-specific studies and further refinement of existing flow metrics to allow more credible transferability of results. The approach used in this study can also be applied to other species sharing life-history strategies for which long-term monitoring data has been compiled and length-at-age relationships established.

The serial discontinuity concept (SDC) proposes that hypolimnetic‐releasing impoundments cause major disruptions to the naturally occurring physical, chemical and biological gradients of rivers but that this impact diminishes with distance downstream. Such a gradient in discharge, flow velocity and temperature regime occurs below a large hypolimnetic‐releasing impoundment, the Hume Dam, on the River Murray in south‐eastern Australia. To examine the effects of this disturbance gradient on a warm‐water large‐bodied freshwater fish, the Murray cod (Maccullochella peelii), a bioenergetics model was developed and calibrated to explore energy expended under differing water velocities and temperature regimes. Model simulations predicted negative growth of juveniles directly downstream of the impoundment, due largely to the energetic costs associated with active and, to a lesser extent, standard metabolism outweighing the achievable energetic gains through food consumption. As flow velocity and temperature regimes became more favourable downstream, so did the simulated growth of the species. It was not until +239 km downstream of the impoundment that the model predicted that flow velocity and temperature regimes were suitable for greater weight gains. The modelled growth responses of juvenile Murray cod are consistent with the predictions of the SDC, emphasising that changes in the bioenergetics of individuals are likely to be reflected in reduced growth rates under the changed flow velocity and temperature regimes imposed by disturbance gradients. This research represents a valuable step in the biological understanding of Murray cod within variable riverine environments and emphasises the urgency required to mitigate impacts associated with hypolimnetic impoundments.

Fish species that have no commercial or recreational value are often overlooked in conservation management, despite serious threats to their long-term future. This can be termed the ‘small threatened freshwater fishes’ paradigm. Population viability analysis (PVA) is a useful technique to assess threatened species and conservation management options. While the development and use of population models and population viability analysis is common in conservation, and often used for larger fishes, this has not been so for small threatened freshwater species. This study uses the PVA process to develop a stochastic population model for Nannoperca australis (southern pygmy perch) in temperate south-eastern Australia. The model was most sensitive to early life-history survival rates, for which there were no estimates from field data, compared with other model uncertainty. This study also found that the oldest age class had the highest reproductive value, providing unique support to the value of big, old, fat and fecund fish (BOFFFs) in sustaining natural populations. Modelling indicated that a population in stable habitat supporting about 2000 female adults would likely to be viable, able to withstand some disturbance and possibly be used as a source population for reintroductions. In reality, however, there are few populations in the wild of sufficient size to withstand such take for translocations and hence the production of fish through hatchery means may be required. This type of approach should prove useful for the conservation management of many similar species globally.

This study profiled the motivations of recreational fishers involved in habitat management activities in Australia, USA, UK and Ireland. Fishers were surveyed using an online questionnaire. Primary motivations for involvement were social (‘putting something back’) rather than to increase fish numbers or improve fishing experience. Fishers were more likely to participate in habitat management if they were members of a club or organisation or self-rated their knowledge of various aspects of fish ecology as very good. Most activities undertaken were relatively simple tasks such as picking up litter and contacting government or the media. Fishers that did not take part in habitat management cited lack of time as the principal reason, but organisational issues (lack of contacts, funding and ideas) were also important. There are considerable opportunities for government agencies and recreational fishing organisations to increase the participation of recreational fishers in habitat management as well as their involvement in more complex tasks through targeted programmes providing contact points, ecological information and administrative support.

A range of perspectives is presented from the International Fisheries Section of the American Fisheries Society on climate change effects on inland fisheries from standing and flowing waters in Africa, Asia, Australia, Europe, and Latin America. Fil: Winfield, Ian J.. Lancaster Environment Centre; Reino Unido Fil: Baigún, Claudio Rafael M.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental; Argentina Fil: Balykin, Pavel A.. Russian Academy of Sciences; Rusia Fil: Becker, Barbara. Pontifícia Universidade Católica de Minas Gerais; Brasil Fil: Chen, Yushun. Chinese Academy of Sciences; República de China Fil: Filipe, Ana F.. Universidade de Lisboa; Portugal. Universidad de Porto; Portugal Fil: Gerasimov, Yuri V.. Russian Academy of Sciences; Rusia Fil: Godinho, Alexandre L.. Universidade Federal de Minas Gerais; Brasil Fil: Hughes, Robert M.. State University of Oregon; Estados Unidos Fil: Koehn, John D.. Government of Victoria. Department of Environment, Land, Water & Planning. Arthur Rylah Institute for Environmental Research; Australia Fil: Kutsyn, Dmitry N.. Russian Academy of Sciences; Rusia Fil: Mendoza Portillo, Verónica. Universidad Nacional Autónoma de México; México Fil: Oberdorff, Thierry. Museum National d'Histoire Naturelle; Francia. Centre National de la Recherche Scientifique; Francia. Universite Pierre et Marie Curie; Francia Fil: Orlov, Alexei M.. Russian Academy of Sciences; Rusia. Dagestan State University. Faculty of Biology. Department of Ichthyology; Rusia. Russian Federal Research Institute of Fisheries and Oceanography; Rusia Fil: Pedchenko, Andrey P.. Berg State Research Institute; Rusia Fil: Pletterbauer, Florian. University of Natural Resources and Life Sciences Vienna; Austria Fil: Prado, Ivo G.. Universidade Federal de Minas Gerais; Brasil Fil: Rösch, Roland. Fisheries Research Station Baden‐Wuerttemberg; Alemania Fil: Vatland, Shane J.. Nez Perce Tribe. Department of Fisheries Resources Management. Research Division; Estados Unidos

Fisheries stock assessments are essential for science-based fisheries management. Inland fisheries pose challenges, but also provide opportunities for biological assessments that differ from those encountered in large marine fisheries for which many of our assessment methods have been developed. These include the number and diversity of fisheries, high levels of ecological and environmental variation, and relative lack of institutional capacity for assessment. In addition, anthropogenic impacts on habitats, widespread presence of non-native species and the frequent use of enhancement and restoration measures such as stocking affect stock dynamics. This paper outlines various stock assessment and data collection approaches that can be adapted to a wide range of different inland fisheries and management challenges. Although this paper identifies challenges in assessment, it focuses on solutions that are practical, scalable and transferrable. A path forward is suggested in which biological assessment generates some of the critical information needed by fisheries managers to make effective decisions that benefit the resource and stakeholders.

Common carp (Cyprinus carpio) are one of the world's most destructive vertebrate pests. In Australia, they dominate many aquatic ecosystems causing a severe threat to aquatic plants, invertebrates, water quality, native fish and social amenity. The Australian Government is considering release of cyprinid herpesvirus-3 (CyHV-3) as a control measure and consequently a robust, continental-scale estimate of the carp population and biomass is essential to inform planning and risk management. Here, we pioneer a novel model-based approach to provide the first estimate of carp density (no/ha) and biomass density (kg/ha) at river reach/waterbody, basin and continental scales. We built a spatial layer of rivers and waterbodies, classified aquatic habitats and calculated the area of each throughout the range of carp in Australia. We then developed a database of fishery-independent electrofishing catch-per-unit-effort (CPUE) for habitat types, containing catch information for 574,145 carp caught at 4831 sites. Eastern Australia accounted for 96% of carp biomass and 92% of the total available wetted habitat area (16,686 km2) was occupied. To correct these data for variable detection efficiencies, we used existing electrofishing data and undertook additional field experiments to establish relationships between relative and absolute abundances. We then scaled-up site-based estimates to habitat types to generate continental estimates. The number of carp was estimated at 199.2 M (95%Crl: 106 M to 357.6 M) for an ‘average’ hydrological scenario and 357.5 M (95%Crl: 178.9 M to 685.1 M) for a ‘wet’ hydrological scenario. In eastern Australia, these numbers correspond with biomasses of 205,774 t (95%Crl: 117,532–356,482 t) (average scenario) and 368,357 t (95%Crl: 184,234–705,630 t) (wet scenario). At a continental scale the total biomass was estimated at 215,456 t for an ‘average’ hydrological scenario. Perennial lowland rivers had the highest CPUE and greatest biomass density (up to 826 kg/ha) and the modelled biomass exceeded a density-impact threshold of 80–100 kg/ha in 54% of wetlands and 97% of stream area in large lowland rivers. The continental-scale biomass estimates provide a baseline for focusing national conservation strategies to reduce carp populations below thresholds needed to restore aquatic ecosystems at a range of spatial scales.

Stock enhancement is an important tool used to rebuild depleted fish populations or enhance recreational fishing. Hatchery-reared individuals can express trait differences, such as growth, which may affect later survival. However, there is little understanding of how early life growth variation affects stocking success. We examined early life growth of golden perch Macquaria ambigua and assessed how growth within hatcheries affects the survival of stocked fish. We measured daily otolith increment widths at 10, 20 and 30 days after hatching, but before stocking into lakes in south-eastern Australia. Mean growth decreased with age, but variation in growth increased. We then compared the early life growth of these individuals to those recaptured after 2 years at liberty (age-2+). Faster individual growth between 20 and 30 days was positively correlated with increased length at stocking. Mean growth between 20 and 30 days of age-2+ fish was higher than that of young-of-year fish, but among-individual variation in growth did not differ between the two groups. These results suggest that individuals with fast hatchery growth have increased survival to 2 years. We propose that enhancing growth within hatcheries may increase the survival of stocked fish, and thus the cost-effectiveness of fish stocking.

The COVID-19 global pandemic and resulting effects on the economy and society (e.g., sheltering-in-place, alterations in transportation, changes in consumer behaviour, loss of employment) have yielded some benefits and risks to biodiversity. Here, we considered the ways the COVID-19 pandemic has influenced (or may influence) freshwater fish biodiversity (e.g., richness, abundance). In many cases, we could only consider potential impacts using documented examples (often from the media) of likely changes, because anecdotal observations are still emerging and data-driven studies are yet to be completed or even undertaken. We evaluated the potential for the pandemic to either mitigate or amplify widely acknowledged, pre-existing threats to freshwater fish biodiversity (i.e., invasive species, pollution, fragmentation, flow alteration, habitat loss and alteration, climate change, exploitation). Indeed, we identified examples spanning the extremes of positive and negative outcomes for almost all known threats. We also considered the pandemic's impact on freshwater fisheries demand, assessment, research, compliance monitoring, and management interventions (e.g., restoration), with disruptions being experienced in all domains. Importantly, we provide a forward-looking synthesis that considers the potential mechanisms and pathways by which the consequences of the pandemic may positively and negatively impact freshwater fishes over the longer term. We conclude with a candid assessment of the current management and policy responses and the extent to which they ensure freshwater fish populations and biodiversity are conserved for human and aquatic ecosystem benefits in perpetuity.

The Murray–Darling Basin (MDB) is Australia’s food bowl, contributing 40% of agricultural production and supporting a population of over 4 million people. Historically, the MDB supported a unique native fish community with significant cultural, subsistence, recreational, commercial and ecological values. Approximately one-quarter of the MDB’s native species are endemic. Changes to river flows and habitats have led to a >90% decline in native fish populations over the past 150 years, with almost half the species now of conservation concern. Commercial fisheries have collapsed, and important traditional cultural practices of First Nations People have been weakened. The past 20 years have seen significant advances in the scientific understanding of native fish ecology, the effects of human-related activities and the recovery measures needed. The science is well established, and some robust restoration-enabling policies have been initiated to underpin actions. What is now required is the political vision and commitment to support investment to drive long-term recovery. We present a summary of 30 priority activities urgently needed to restore MDB native fishes.

Many freshwater fishes are imperilled globally, and there is a need for easily accessible, contemporary ecological knowledge to guide management. This compendium contains knowledge collated from over 600 publications and 27 expert workshops to support the restoration of 9 priority native freshwater fish species, representative of the range of life-history strategies and values in south-eastern Australia’s Murray–Darling Basin. To help prioritise future research investment and restoration actions, ecological knowledge and threats were assessed for each species and life stage. There is considerable new knowledge (80% of publications used were from the past 20 years), but this varied among species and life stages, with most known about adults, then egg, juvenile and larval stages (in that order). The biggest knowledge gaps concerned early life stage requirements, survival, recruitment, growth rates, condition and movements. Key threats include reduced longitudinal and lateral connectivity, altered flows, loss of refugia, reductions in both flowing (lotic) and slackwater riverine habitats, degradation of wetland habitats, alien species interactions and loss of aquatic vegetation. Examples and case studies illustrating the application of this knowledge to underpin effective restoration management are provided. This extensive ecological evidence base for multiple species is presented in a tabular format to assist a range of readers.

Increased regulation and extraction of water from rivers has contributed to the decline of fishes, and the use of environmental water allocations (EWAs) is now a key rehabilitation measure. Major reform of water policy in the Murray-Darling Basin (MDB), Australia, has recently provided significant EWAs to improve ecological outcomes. Conflict over water buybacks, the value of the water and the need to maximise environmental benefits and minimise risks of unwanted outcomes has increased the expectation for science to underpin and justify such actions. Recent research has focussed attention on the need to understand fish–flow relationships. The Native Fish Strategy for the Murray-Darling Basin 2003–2013 (NFS), while not specifically targeted at water policy reform or water delivery, has provided fish ecology research and flow restoration experimentation and contributed considerable new scientific knowledge to support flow management. It has contributed to a substantial and positive change in environmental watering for fish, with native fish targets now regularly incorporated into watering objectives. This study documents changes to water management in the MDB, summarises current knowledge of flow-related fish ecology in the MDB, highlights the benefits and risks of some water management practises and provides recommendations for future management and research. A major recommendation is the need for a coordinated, cross-jurisdictional approach to flow restoration for native fish, ensuring that the best available science is being used in all watering allocations. We caution on the use of environmental works such as regulators to artificially inundate floodplains and suggest that such approaches should be viewed as large-scale experiments with the significant risks posed to fish needing to be recognised, adequately monitored and adaptively managed.

The Native Fish Strategy aimed to return fish populations in Australia's largest (1 million square kilometre) river basin from an estimated 10 to 60% of pre-European settlement levels after 50 years of implementation. While funding for implementation of this programme has now ceased (despite native fish remaining in a poor state), the achievements of the Strategy's first 10 years provide a solid basis for implementing the work necessary to rehabilitate native fish populations in the future.

Sustainable management of natural resources requires robust and timely information inputs, particularly in multispecies or cross-jurisdictional fisheries such as the Murray-Darling Basin's (MDB) recreational fishery. Innovative data collection and monitoring approaches, management tools and cooperative efforts enable the requirements of fisheries managers to be met efficiently and cost-effectively. This paper considers a number of pioneering initiatives operationalised under the Native Fish Strategy that have helped inform sustainable management outcomes for the recreational fishery in the MDB.

The Murray–Darling Basin (MDB) covers 1.1 million km2, involves six legislative jurisdictions, a myriad of different agencies and illustrates the many complexities of managing fishes, people and water. Its rivers provide water for agriculture, are highly regulated and generally in poor health. Water allocation reform is underway to improve ecological condition but provision of water for environmental outcomes competes with agricultural requirements. Murray–Darling Basin rivers and fishes are important culturally and contribute substantially to tourism and recreational fishing. The MDB has a low number of fish species, now estimated to be at 10% of their pre-European abundance, and all subject to a range of threats, many related to water use and associated infrastructure. The MDB Native Fish Strategy takes a coordinated, long-term, whole-of-fish-community approach to address priority threats and rehabilitate populations. This strategy provides a holistic approach with many actions that complement the potential benefits of water reform.

Carp are a highly successful invasive fish species, now widespread, abundant and considered a pest in south-eastern Australia. To date, most management effort has been directed at reducing abundances of adult fish, with little consideration of population growth through reproduction. Environmental water allocations are now an important option for the rehabilitation of aquatic ecosystems, particularly in the Murray–Darling Basin. As carp respond to flows, there is concern that environmental watering may cause floodplain inundation and provide access to spawning habitats subsequently causing unwanted population increase. This is a management conundrum that needs to be carefully considered within the context of contemporary river flow management (natural, environmental, irrigation). This paper uses a population model to investigate flow-related carp population dynamics for three case studies in the Murray–Darling Basin: (1) river and terminal lakes; (2) wetlands and floodplain lakes; and (3) complex river channel and floodplain system. Results highlight distinctive outcomes depending on site characteristics. In particular, the terminal lakes maintain a significant source carp population regardless of river flow; hence any additional within-channel environmental flows are likely to have little impact on carp populations. In contrast, large-scale removal of carp from the lakes may be beneficial, especially in times of extended low river flows. Case studies 2 and 3 show how wetlands, floodplain lakes and the floodplain itself can now often be inundated for several months over the carp spawning season by high volume flows provided for irrigation or water transfers. Such inundations can be a major driver of carp populations, compared to within channel flows that have relatively little effecton recruitment. The use of a population model that incorporates river flows and different habitats for this flow-responsive species, allows for the comparison of likely population outcomes for differing hydrological scenarios to improve the management of risks relating to carp reproduction and flows.

Murray cod Maccullochella peelii (Mitchell) is a large, iconic Australian fish species targeted by anglers but also listed as nationally threatened. A consultative process that included conservation and fishery interests helped to develop a population model for this species and agree on management scenarios to be tested. The modelled scenarios illustrated that threats to populations (risk of decline) can be substantially reduced and catch rates increased through harvest slot length limits (HSLL) rather than minimum legal limits (MLL). A 600- to 1000-mm HSLL provided lower risk of decline and greater catch rates than the existing 500-mm MLL, but better results were achieved with a 400- to 600-mm HSLL. Importantly, a range of other impacts (fish kills, stocking, thermal impacts, larval mortalities, habitat changes) were recognised and incorporated. This study provides an example of the utility of a population model to improve management decision-making for both conservation and fishery objectives.

There is much interest in managing invasive freshwater fish, but little is known about the dynamics of these populations following establishment. We used annual commercial catch-per-unit-effort data at multiple spatio-temporal scales to test hypotheses about the population dynamics of invading common carp (Cyprinus carpio) in the Murray-Darling Basin, Australia. We hypothesised that following establishment of the Boolara strain of this species in the Murray-Darling Basin in 1961/1962: (1) carp would undergo exponential or logistic-type population growth; and (2) carp population growth rates would be highest following over-bank flood events that provided extensive off-channel spawning and feeding habitats. The logistic (wi = 0.73) and delayed-logistic (wi = 0.27) models best explained the population dynamics of common carp in the Murray-Darling Basin during 1962/1963–2001/2002; there was negligible support for exponential growth (wi ≤ 0.01). Although we cannot exclude the possibility that floods may have been important in the early years of the invasion we found little evidence that carp population growth rates increased following flood events. Our logistic-type model-based estimates of the maximum annual population growth rate (rm; 0.378 and 0.384) indicate that >0.315 or 0.319 of the adult population would need to be removed annually to achieve eradication. We conclude that the rapid spread of the Boolara strain of common carp through the Murray-Darling Basin was facilitated by high initial population growth rates. More generally, we suggest that the lag period between an invader establishing and increasing to high abundances will be characterised by logistic-type population growth. We encourage others to investigate the long-term population dynamics of invading freshwater fish using time series and models such as those reported here.

MDFRC item.First published online March 2012.Bayesian belief networks (BBNs) are a widespread tool for modelling the effects of management decisions and activities on a variety of environmental and ecological responses. Parameterisation of BBNs is often achieved by elicitation involving multiple experts, and this may result in different conditional probability distribution tables for the nodes in a BBN. Another common use of BBNs is in the comparison of alternative management scenarios. This paper describes and implements the 'belief index' (BI), an empirical measure for evaluating outcomes in BBN modelling that summarises the probabilities (or beliefs) of any one node in a BBN. A set of four species-specific BBNs for managing watering events for wetland fish is outlined and used to statistically assess between-expert and between-species variability in parameter estimates by means of the BI. Different scenarios for management decisions are also compared using the % improvement measure, a derivative of the BI.

The Native Fish Strategy (NFS) for the Murray-Darling Basin, south-eastern Aus- tralia, provides a whole-of-fish-community approach and coordinated direction for the rehabilita- tion of its severely degraded native fish populations. Together with actions outlined in recovery plans for threatened species, the NFS addresses priority threats identified for native fishes with the aim to rehabilitate native fish populations to 60% (current populations are estimated to be at about 10%) of the levels that existed prior to European settlement. The NFS has a 50 yr time frame and coordinates actions across 6 different management jurisdictions. A key component of the NFS is the engagement of communities and stakeholders, with this being undertaken, in particular, by the use of dedicated coordinators and the development of 'demonstration reaches' where rehabil- itation can be undertaken using multiple actions, with community involvement. The NFS is sup- ported by targeted research projects and monitoring within an adaptive management framework. The NFS provides an effective partnership model where central coordination, coupled with focused jurisdictional actions, can deliver benefits to all governments. It synthesises and dissemi- nates knowledge, integrates research and management and catalyses actions for priority prob- lems. The need, objectives, evolution and development, achievements, strengths and weaknesses of the NFS are presented. The NFS approach would be suitable for many large river basins throughout the world.

MDFRC item.Wetlands are productive and diverse habitats for native fish but can be highly degraded, particularly in the Murray-Darling Basin (MDB), south-eastern Australia. Wetland management requires tools and processes that facilitate the synthesis and application of knowledge for decisions concerning the allocation of environmental water to wetlands to improve environmental outcomes. This paper describes the development of a Decision Support Tool (DST), based on a Bayesian Network designed to provide the best available science and support adaptive management of environmental flows into wetlands. The DST predicts the probability of improvements in fish population health as defined by abundance, population structure and fish condition for introduced common carp and three native species of fish: carp gudgeon, Australian smelt, and golden perch. Model sensitivity and validation showed that fish response varied depending on model inputs, but that responses from the DST were an accurate reflection of fish responses in wetlands based on field data. Ultimately, the success of this DST is dependent on its adoption by wetland managers. Throughout the entire development process, adoption of the DST has been promoted through engagement with managers and subsequently, through initiatives to integrate it into current management initiatives.

Understanding the influence of extrinsic factors such as hydrology and hydraulics on recruitment provides essential insight to inform management of fish populations. The critically endangered silver perch Bidyanus bidyanus is a long-lived, potamodromous pelagophil endemic to Australia’s Murray–Darling Basin. Declines of this species are often attributed to river regulation, although quantitative studies linking hydrology and hydraulics to key aspects of its life cycle are sparse. We used a multidecadal age-structured dataset collected from a locally abundant population of silver perch to quantify the relative importance of different abiotic drivers on year-class strength (recruitment). Silver perch recruited across highly variable hydrological conditions. The strongest year classes were associated with a combination of low to average river discharge (i.e. within channel) and high water temperatures over the peak spawning period, followed in the next year by extended high flows and widespread flooding that promoted survival of age-1+ juvenile fish. We suggest that conditions affecting the growth and dispersal of juvenile fish, in addition to the spawning period, are critical in governing recruitment dynamics. This highlights the need for multiyear flow plans for freshwater fish populations.

Irrigated agriculture and inland fisheries both make important contributions to food security, nutrition, livelihoods and wellbeing. Typically, in modern irrigation systems, these components operate independently. Some practices, commonly associated with water use and intensification of crop production can be in direct conflict with and have adverse effects on fisheries. Food security objectives may be compromised if fish are not considered in the design phases of irrigation systems. The 2030 Agenda for Sustainable Development provides a framework that can serve as a backdrop to help integrate both sectors in policy discussions and optimise their contributions to achieving the Sustainable Development Goals (SDGs). Inland fisheries systems do play an important role in supporting many SDG objectives, but these contributions can sometimes be at odds with irrigated agriculture. Using case studies of two globally important river catchments, namely the Lower Mekong and Murray–Darling basins, we highlight the conflicts and opportunities for improved outcomes between irrigated agriculture and inland fisheries. We explore SDG 2 (Zero Hunger) as a path to advance our irrigation systems as a means to benefit both agriculture and inland fisheries, preserving biodiversity and enhancing the economic, environmental and social benefits they both provide to people.2

A common approach to nature conservation is to identify and protect natural 'assets' such as ecosystems and threatened species. While such actions are essential, protection of assets will not be effective unless the ecological processes that sustain them are maintained. Here, we consider the role of ecological processes and the complementary perspective for conservation arising from an emphasis on process. Many kinds of ecological processes sustain biodiversity: including climatic processes, primary productivity, hydrological processes, formation of biophysical habitats, interactions between species, movements of organisms and natural disturbance regimes. Anthropogenic threats to conservation exert their influence by modifying or disrupting these processes. Such threats extend across tenures, they frequently occur offsite, they commonly induce non-linear responses, changes may be irreversible and the full consequences may not be experienced for lengthy periods. While many managers acknowledge these considerations in principle, there is much scope for greater recognition of ecological processes in nature conservation and greater emphasis on long time-frames and large spatial scales in conservation planning. Practical measures that promote ecological processes include: monitoring to determine the trajectory and rate of processes; incorporating surrogates for processes in conservation and restoration projects; specific interventions to manipulate and restore processes; and planning for the ecological future before options are foreclosed. The long-term conservation of biodiversity and the well-being of human society depend upon both the protection of natural assets and maintaining the integrity of the ecological processes that sustain them.

– This study of Murray cod (Maccullochella peelii peelii) movements in a large lowland river in south-eastern Australia indicated that the species was not sedentary, but undertook complex movements that followed a seasonal pattern. While there were sedentary periods with limited home ranges and high site fidelity, Murray cod also under took larger movements for considerable portions of the year coinciding with its spawning schedule. This generally comprised movements (up to 130 km) from a home location in late winter and early spring to a new upstream position, followed by a rapid downstream migration typically back to the same river reach. Timing of movements was not synchronous amongst individuals and variation in the scale of movements was observed between individuals, fish size, original location and years.

We used radiotelemetry and mark-recapture tagging to determine the spatial move- ments of adults and juveniles (>180 mm total length) of a federally endangered, native Percichthyid fish, the trout cod Maccullochella macquariensis, in the Murray River, south-eastern Australia, to assist in its management and conservation. Trout cod exhibited strong evidence for site fidelity and homing in this study, typically utilizing only a few locations in the river channel and undertaking limited movements. The home range estimate for radiotracked fish was 61 ± 46 m (95% confidence interval). Movements of 1200 ± 46 m (95% confidence interval) were recorded for mark-recapture fish over longer time frames. No movements were recorded for 50% of fish. Larger movements (>3 km) were observed in

Trout cod (Maccullochella macquariensis, Cuvier) is a critically endangered species that now only occurs naturally in a 200 km reach of the Murray River in south-eastern Australia. An assessment of its habitat use was undertaken using radio telemetry to test the assumptions underlying conservation strategies for the species. Trout cod were more likely to be observed in deeper water associated with the low-flow channel. The importance of large wood habitat was dependent on its location within the river channel. In narrow river sections trout cod utilised location where large wood was abundant. In other locations, large wood was associated with deep scour pools that were utilised by trout cod. Our results support rehabilitation of large wood habitat in streams where this was a natural feature as part of the recovery program for this species.

A one-dimensional hydrodynamic reservoir model is coupled with a stochastic fish population model to examine the impacts of cold water pollution (CWP) on the Australian freshwater fish, Murray cod, downstream of Hume Dam, Australia. Mitigation of CWPthroughtheintroductionofselectivewithdrawalcapabilitiestoaccessnear-surfacewaterispredictedtoincreasedischarge temperatures during the crucial spring-early summer post-spawning period by 4‐68C for normal operating conditions, that is, a full reservoir in early spring. No improvement in discharge temperature was predicted for drought conditions characterized by relatively low storage levels in early spring. The predicted temperature increase using selective withdrawal increased the predicted average minimum female population abundance by 30‐300% depending on the assumed spawning behaviour. Increased discharge temperatures appear to be achievable and are expected to reduce the stress currently impacting Murray cod populations due to CWP during crucial post-spawning periods. This provides evidence that mitigation of this problem may assistinrehabilitatingMurraycodpopulationsintheMurrayRiverdownstreamofHumeDam.Copyright#2007JohnWiley& Sons, Ltd.

The environmental conditions and timing of spawning of Murray cod and trout cod were investigated over three successive years in the regulated Murray River and in the nearby, unregulated Ovens River. Larvae were collected in drift samples from early November. Murray cod larvae were present for up to ten weeks, but trout cod larvae were present for only about two weeks. Cod larvae were collected in both rivers in each year sampled, despite a range of flow conditions. Spawning periods, estimated by back-calculating larval ages and egg incubation times, were in part, concurrent for the two species, beginning in October when water temperatures had exceeded 15°C, allowing the occasional hybridization that has been noted between these two species. Trout cod larvae (10.0–18.2 mm) were significantly larger than Murray cod larvae (9.5–14.8 mm) in both years and the larvae of both species were significantly larger in 1995/6 than in 1994/5 in the Murray River. There was no relationship between larval size and water temperature, but later spawning times at the upper Murray River site coincided with lower water temperatures. Larval abundance varied significantly between sites, samples and years, with peak larval abundances occurring in November. Murray cod larval abundance was best explained by the explanatory variables of year, day length and change in flow over the previous 7 d. Environmental conditions for the spawning of Murray cod and trout cod are similar, and both species exhibit a similar larval dispersal strategy by emergence into the drift. Spawning occurred regularly under a range of flow conditions and it is likely that recruitment of these species in these rivers is driven by the subsequent survival of larvae and juveniles. Copyright © 2005 John Wiley & Sons, Ltd.

1. The importance of structural woody habitat (SWH) as instream fish habitat in eastern Australia has been well documented. In response, many native fish restoration programmes are returning SWH to rivers where it had previously been removed. However, there is little information to direct the placement of this SWH within a river landscape. 2. Low-level, high-resolution aerial photographs were used to investigate the spatial pattern of SWH in the Murray River between Lake Mulwala and Tocumwal. It was found that SWH occurred in aggregations that were closely associated with eroding banks on meanders. 3. The physical characteristics of the SWH in these aggregations varied (basal diameter range 0.44–2.45 m, length range 1–44 m); however, small- to medium-sized trees (basal diameter range 0.7–1.4 m, length range 5–20 m) were most common. 4. The association between eroding banks and SWH suggests that bank erosion may be an important determinant in the formation of SWH aggregations. Copyright © 2004 John Wiley & Sons, Ltd.