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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.

Understanding connectivity is crucial for the effective conservation and management of biota. However, measuring connectivity directly is challenging and it is often inferred based on assumptions surrounding dispersal potential, such as environmental history and species life history traits. Genetic tools are often underutilised, yet can infer connectivity reliably. Here, we characterise and compare the genetic connectivity and genetic diversity of three diadromous Australian fish species: common galaxias (Galaxias maculatus), tupong (Pseudaphritis urvillii) and Australian grayling (Prototroctes maraena). For each species, we investigate the extent of genetic connectivity across a study region in south-eastern Australia (~700 km). We further determine the potential roles of contemporary ocean currents in shaping the patterns of genetic connectivity observed. Individuals across multiple rivers were sampled and >3000 single nucleotide polymorphisms were genotyped for each species. We found differences in genetic connectivity for the three species: common galaxias were highly connected, and Australian grayling and tupong exhibited patterns of isolation by distance. The degree of genetic connectivity for tupong and Australian grayling appeared unrelated to oceanic currents. This study indicates that the degree of connectivity for different diadromous species can vary greatly despite broadly similar life history strategies, highlighting the potential value of genetic tools for informing species-specific management plans.

Through using different sources, population reintroductions can create genetically diverse populations at low risk of harmful inbreeding and well equipped for adaptation to future environments. Genetic variation from one source can mask locally nonoptimal alleles from another, thereby enhancing adaptive potential and population persistence. We assessed the outcomes in survival, growth and reproduction of using two differentiated sources (genetically diverse Yarra and moderately diverse Dartmouth) for translocations and stocking to reintroduce the endangered Australian freshwater Macquarie perch Macquaria australasica into the Ovens River. For stocking, same‐ and different‐population parents (“cross‐types”) were used during hatchery production. Genetic samples and data on individual fish were collected over three years of monitoring the Ovens. We genetically assigned Ovens fish to their broodstock parents and tested whether cross‐type and genetic dissimilarity between parents are associated with offspring survival, and whether cross‐type and parental dissimilarity or individual genetic diversity are associated with somatic growth rates of stocked fish. We genetically identified translocated fish and assessed local recruit ancestry. Of 296 Ovens fish, 31.1% were inferred to be stocked, 1.3% translocated and 67.6% locally born. Cross‐type strongly predicted survival of stocked offspring: those with two Yarra parents had the highest survival, followed by offspring with two‐population, then Dartmouth, ancestry. Of the Ovens recruits, 59.5% had Yarra, 33.5% two‐population and 7.0% Dartmouth ancestry, despite 67% of stocked and 98% of translocated fish originating from Dartmouth. Offspring with two Yarra parents grew faster than offspring of Dartmouth or two‐population ancestry. Although Dartmouth fish appear to be less fit in the Ovens compared to Yarra fish, possibly due to deleterious variation or genetic or plastic maladaptation, they contribute to the reintroduced population through local interbreeding with Yarra fish and relatively high survival of stocked offspring of two‐population ancestry. Thus, combining compatible stocks is likely to benefit restoration of other wildlife populations.

Most predictions for the future climate in temperate ecosystems show longer periods of drought followed by more extreme precipitation events. These changes in flow regimes can strongly affect riverine fish populations; therefore, assessing the recovery of populations following these episodic events provides important information to help guide species management. This study investigated the dynamics of 5 spatially distinct riverine populations of the nationally endangered Macquarie perch Macquaria australasica in southeastern Australia from 2007-2018, a period that included the tail end of a decadal long drought followed by extreme fluctuations in river flow. Modelling catch rates and size trends, we found that 4 of the 5 populations showed some synchrony and underwent a slow recovery that was undetectable for several years. The largest increases in population size were driven by the survival of new recruits. Despite this general trend, we could only find a weak association between annual flow extremes and annual population change. This suggests intermediate variations in river flows may have a negligible influence on annual population change or are idiosyncratic in their effect within each waterway or on different life stages. The one population which did not follow this trend occurred in the largest waterway and was subject to legal recreational fishing, suggesting the magnitude of impacts of disturbance on populations occupying larger systems are reduced, and/or that recreational fishing hinders recovery rates following episodic disturbance events such as drought. Our results suggest that forecasting and management of long-lived freshwater fish must incorporate multi-year planning to include factors such as the maintenance of refuges, connectivity and increased protection of mature fish to aid recovery.

Understanding how and why the size of populations varies is critical knowledge for conservation and management. While considerable work has explored how different demographic parameters affect population growth, less is known the drivers of variability in these parameters. Long-term time series tracking population size that are coupled with empirical data to examine the relative importance of different drivers are rare, especially in freshwater systems. Even rarer are studies that collect this information concurrently from multiple species with contrasting life history strategies in the same system to assess whether population size and the relative importance of drivers also vary. We studied changes in the abundance and size structure of four native freshwater fish species in the Murray River, southeastern Australia, over a continuous 19-yr period. Two species with traits typical of "equilibrium" species (Murray cod Maccullochella peelii and trout cod Maccullochella macquariensis) and two with traits of "periodic" species (golden perch Macquaria ambigua and silver perch Bidyanus bidyanus) were sampled annually and capture-mark-recapture modeling was used to ask (1) how did population size change during this period, (2) how were changes in population size related to variability in hydrology, and (3) how were changes in population size driven by different processes (local recruitment or migration events)? Populations of all four species varied throughout the study, and our results are consistent with the notion that local recruitment is an important driver of this variability for Murray cod and trout cod, whereas immigration is more important for the two other species. Increases in spring river discharge strongly influenced these responses for trout cod and golden perch. Our study provides fundamental insights into the population dynamics of these valued species, and how management strategies might differ based on their life histories. Management should focus on allowing connectivity for golden and silver perch, and on promoting local scale recruitment and survival for Murray cod and trout cod. More generally, our study highlights the importance of understanding the processes underpinning population persistence, how these processes may vary for different species, and ultimately how this knowledge can inform targeted management actions.

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.

In many animal populations, demographic parameters such as survival and recruitment vary markedly with age, as do parameters related to sampling, such as capture probability. Failing to account for such variation can result in biased estimates of population‐level rates. However, estimating age‐dependent survival rates can be challenging because ages of individuals are rarely known unless tagging is done at birth. For many species, it is possible to infer age based on size. In capture–recapture studies of such species, it is possible to use a growth model to infer the age at first capture of individuals. We show how to build estimates of age‐dependent survival into a capture–mark–recapture model based on data obtained in a capture–recapture study. We first show how estimates of age based on length increments closely match those based on definitive aging methods. In simulated analyses, we show that both individual ages and age‐dependent survival rates estimated from simulated data closely match true values. With our approach, we are able to estimate the age‐specific apparent survival rates of Murray and trout cod in the Murray River, Australia. Our model structure provides a flexible framework within which to investigate various aspects of how survival varies with age and will have extensions within a wide range of ecological studies of animals where age can be estimated based on size.

A growing worldwide body of literature is demonstrating the geomorphic and ecological roles played by wood in rivers. After more than a century of removing wood from rivers in many parts of the world, researchers and managers are now interested in returning the load of wood back to a more natural condition. The mechanical placement of wood in rivers is expensive, and so it is useful to know how long it will take for in‐stream wood loads to passively recover a target load by recruitment from riparian forests. Of fundamental interest to managers and researchers alike are the questions: (1) can a river passively recover to a preremoval load of wood, and (2) if so, how long will recovery take? We address these questions using the example of the anabranching King River, Northeast Victoria, Australia, which was desnagged twice: once in 1957 and again in 1980. We predict a recovery time of 255 ± 23 years using a complete census of recovering wood loads to develop and parameterize a mass balance delivery model run in a Monte Carlo simulation. Our results indicate that with a healthy supply of riparian vegetation and minimal interference from managers, rivers are likely to passively recover natural wood loads at least two and a half centuries after desnagging. Using the data and methods described in this paper, we develop a theory of recovery, conceptually describing the recovery process as a sequence of five stages that can be used to monitor and track wood loads through time.

Anthropogenic alterations to river flow regimes threaten freshwater biodiversity globally, with potentially disproportionate impacts on species that rely on flow cues to trigger critical life history processes, such as migration for diadromous fishes. This study investigates the influence of river discharge on the abundance of juvenile fish moving into rivers by four temperate catadromous or amphidromous species (common galaxias Galaxias maculatus, spotted galaxias Galaxias truttaceus, climbing galaxias Galaxias brevipinnis and the threatened Australian grayling Prototroctes maraena). Fyke netting or fishway trapping was used to catch juvenile fish moving from estuaries into freshwater in five coastal waterways in south-eastern Australia during the spring migratory period. There was a positive relationship between the probability of high catch rates and mean discharge in September. We also found a positive relationship between discharge and the number of recruits captured 22-30 days later in a flow stressed system. In addition, day-of-year had a strong influence on catch rates, with the peak abundance of juveniles for three species most likely to occur midway through the sampling period (spotted galaxias in October, climbing galaxias in late October and Australian grayling in late October and early November). Our study shows that higher magnitudes of river discharge were associated with increased catches of juvenile catadromous and amphidromous fishes. With a limited supply of environmental water, environmental flows used to enhance immigration of these fishes may be best targeted to maintain small amounts of immigration into freshwater populations in waterways or years when discharges are low and stable. When there are natural, large discharge volumes, relatively large numbers of juvenile fish can be expected to enter coastal waterways and during these times environmental flows may not be required to promote immigration.

River regulation has degraded aquatic biodiversity globally, and the effects can be pronounced for diadromous species, whose life history processes can depend on flow conditions, such as cues for adult migration, spawning, attracting recruits into coastal rivers and promoting upstream dispersal. Environmental flows are being used to mitigate the effects of river regulation, and understanding their effectiveness is required to improve management practices. This study examined the effects of targeted environmental flows on the upstream dispersal of three temperate catadromous fish species, namely common galaxias Galaxias maculatus, tupong Pseudaphritis urvillii and short-finned eel Anguilla australis. Fyke netting was used to capture fish moving upstream before and during environmental flows in summer and autumn in two coastal rivers. We found significant increases in the catch of young-of-the-year (YOY) common galaxias (6-fold higher) and juvenile short-finned eel (26-fold higher), relative to control sites, during environmental flow pulses compared with stable, regulated base-flow conditions. A significant response was not detected for YOY tupong, despite a 39% increase in the catch. These results demonstrate that environmental flows enhance the upstream movement of juvenile diadromous fishes, a critical process governing population persistence or recovery. The findings provide managers with confidence in the use of environmental flows to support populations.

© 2020 Journal Compilation Effective fisheries management requires fish size, growth and mortality information representative of the population and location of interest. Golden perch Macquaria ambigua is long lived, potamodromous and widespread in the Murray-Darling Basin (MDB), Australia. Using a sample spanning 13 river systems and 10° of latitude, we examined whether the maximum size of golden perch differed by latitude and whether growth and mortality varied between northern and southern MDB regions. The length, weight and age ranges of golden perch sampled (n = 873) were 52-559 mm, 2-3201 g and 0+ to 26+ years respectively, and maximum length and weight were unaffected by latitude. Length and age-length distributions represented by age-length keys varied by region, with greater variability in age-at-length and a larger proportion of smaller individuals in northern MDB rivers, which generally exhibit greater variability in discharge. Growth and mortality rates were similar between regions, and an MDB-wide von Bertalanffy growth model (L∞ = 447, k = 0.32 and t0 = -0.51) and instantaneous mortality rate (Z = 0.20) best described the data. An MDB-wide length-weight equation also provided the best fit (W = 6.76 × 10-6 L3.12). Our data suggest that the MDB can be treated as one management unit in terms of golden perch maximum size, growth and mortality parameters.

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 intrapopulation variability in the size and age structure of the spawning stock and migration of the threatened Macquarie perch Macquaria australasica in Lake Dartmouth was investigated between 2008 and 2016. Sampling centred on the core reproductive period (October-December) when mature fish migrate from the lake into riverine habitat to spawn. Spawning fish were predominantly large, spanning a broad age structure, with a high proportion of fish (25%) aged 15-30 years. The overall median size of spawning fish did not change for males or females during the 9 year study period. The size of the smaller mature male fish did change in some years suggesting a small proportion of male M. australasica matured at age 1+ and 2+. Acoustic telemetry employed over 3 years showed that M. australasica were most likely to be in the spawning reach from October to mid-December, migrated to this reach annually and moved large distances throughout the lake all year, with no evidence for any spatial structuring. Mature fish sometimes occupied the spawning reach for several months after the core reproductive period, which increased their vulnerability to recreational fishing. Males tagged in the lake were seldom recorded in the spawning reach, presumably because a high proportion had not yet entered the spawning stock despite their size suggesting maturity. Maintaining a broad age and size-structure of the spawning stock of long-lived iteroparous fish species is crucial for recruitment stability and population persistence. Overexploitation of the spawning stock has probably contributed to previous population declines in the lake as well as the collapse of other M. australasica populations in south-eastern Australia.

Adaptive differences across species’ ranges can have important implications for population persistence and conservation management decisions. Despite advances in genomic technologies, detecting adaptive variation in natural populations remains challenging. Key challenges in gene-environment association studies involve distinguishing the effects of drift from those of selection, and identifying subtle signatures of polygenic adaptation. We used paired-end restriction-site associated-DNA sequencing data (6605 biallelic single nucleotide polymorphisms; SNPs) to examine population structure and test for signatures of adaptation across the geographic range of an iconic Australian endemic freshwater fish species, the Murray cod Maccullochella peelii. Two univariate gene-association methods identified 61 genomic regions associated with climate variation. We also tested for subtle signatures of polygenic adaptation using a multivariate method (redundancy analysis; RDA). The RDA analysis suggested that climate (temperature- and precipitation-related variables) and geography had similar magnitudes of effect in shaping the distribution of SNP genotypes across the sampled range of Murray cod. Although there was poor agreement among the candidate SNPs identified by the univariate methods, the top 5% of SNPs contributing to significant RDA axes included 67% of the SNPs identified by univariate methods. We discuss the potential implications of our findings for the management of Murray cod and other species generally, particularly in relation to informing conservation actions such as translocations to improve evolutionary resilience of natural populations. Our results highlight the value of using a combination of different approaches, including polygenic methods, when testing for signatures of adaptation in landscape genomics studies. This article is protected by copyright. All rights reserved.

Fish are often targets for environmental watering outcomes under the premise that aspects of the flow regime are linked to key components of their life-history. This study examined the conceptual link between variability in river discharge and fish productivity by measuring annual growth patterns (generated using sclerochronology over a 22-year period) of two native freshwater cod Maccullochella spp. species over a range of flow conditions in a regulated Australian floodplain River. We found a positive relationship between fish growth, flow variability and river discharge. Flow variability during spring and summer-autumn, as well as their antecedent values, was particularly important in explaining annual growth of the nationally endangered Maccullochella macquariensis. Growth of Maccullochella peelii displayed similar patterns, though were more closely aligned with spring discharge. These results are consistent with the general view that increased river regulation, due to its suppression of flow magnitude and variability, has been a major contributing factor in the decline of native fish populations throughout the world. Our results provide support and guidance for the use of environmental water delivery, and have broad application to rivers worldwide for which any quantification of ecological impacts of regulation, and responses to water management remain scarce.

Most assessments of the effectiveness of river restoration are done at small spatial scales (

Reporting uncertainty in environmental measurements and estimates is important for cross-comparison and inter-comparison of sites and other spatial units. One such measure is the load of large in-stream wood in river systems. In this paper we propose the use of the Weibull distribution to describe the central tendency and variability of wood loads along a river reach. We illustrate the link between the average wood load and the central tendency or scale parameter of the Weibull distribution. The shape of the Weibull distribution is strongly related to the ability of rivers to transport and rearrange the wood in a reach. We use six Victorian rivers to test the fit of the Weibull distribution, showing that the Weibull is a useful and flexible distribution that provides common reporting metrics useful for future studies. Using common reporting metrics provides a stronger tool for comparisons of wood loads between rivers and with reaches. Copyright © 2016 John Wiley & Sons, Ltd.

Genetic variation is critical to the persistence of populations and their capacity to adapt to environmental change. The distribution of genetic variation across a species' range can reveal critical information that is not necessarily represented in species occurrence or abundance patterns. We identified environmental factors associated with the amount of intraspecific, individual-based genetic variation across the range of a widespread freshwater fish species, the Murray cod Maccullochella peelii. We used two different approaches to statistically quantify the relative importance of predictor variables, allowing for nonlinear relationships: a random forest model and a Bayesian approach. The latter also accounted for population history. Both approaches identified associations between homozygosity by locus and both disturbance to the natural flow regime and mean annual flow. Homozygosity by locus was negatively associated with disturbance to the natural flow regime, suggesting that river reaches with more disturbed flow regimes may support larger, more genetically diverse populations. Our findings are consistent with the hypothesis that artificially induced perennial flows in regulated channels may provide greater and more consistent habitat and reduce the frequency of population bottlenecks that can occur frequently under the highly variable and unpredictable natural flow regime of the system. Although extensive river regulation across eastern Australia has not had an overall positive effect on Murray cod numbers over the past century, regulation may not represent the primary threat to Murray cod survival. Instead, pressures other than flow regulation may be more critical to the persistence of Murray cod (for example, reduced frequency of large floods, overfishing and chemical pollution).

Managers and communities are now artificially reintroducing instream woody habitat (IWH) to rivers following historic large-scale removal. Riverscape-scale datasets that quantify existing habitat conditions are fundamental to setting the priorities and allocating resources for such programs. Unfortunately, such datasets are rare, primarily because existing assessment approaches are limited in their accuracy (remote sensing) or are costly and labour intensive (field assessments). This study used both field assessments and aerial data to improve the accuracy of remotely sensed measures of IWH and estimate current IWH volumes and subsequent condition (compared with reference levels) across approximately 28 000 km of stream in the south-eastern Australian state of Victoria. We found that aerial measures, when used in conjunction with measures of stream size and riparian overhang, produced significantly better estimates of IWH loads than using aerial data alone. The statewide assessment indicated that streams currently have IWH volumes, on average, 41% lower than reference levels that represented an average reduction of 0.0207 m3 m−2. The degree of IWH condition was highly variable across regions (20–95% reductions from reference levels), a likely reflection of regional variation in land use practices and past river work activities. This scale of IWH reduction may pose major negative impacts on the ecological integrity of these streams. Whilst the approach used during this study has temporal and spatial limitations, it was designed as a generalised, rapid and relatively inexpensive method to measure stream condition and assist with priority setting at state and regional levels. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Summary 1. Environmental flows are a key restoration technique for conserving ecological function in flow-degraded rivers. Species-specific, flow–biota relationships are increasingly being used to determine environmental flow needs and manage their use; however, many of these relationships are poorly described. 2. We evaluate relationships between environmental variables and spawning intensity for a fish assemblage from the Murray River, Australia, over a ten-year period. We developed a hierarchical multispecies model that accounted for incomplete detection to compare spawning outcomes of native and non-native species using realistic, alternative, water management scenarios. 3. Temperature was an important predictor of spawning intensity for all seven species studied, while both concurrent and antecedent flow conditions were important for many species. Our water management scenario testing accounted for these relationships and indicated that increasing the magnitude of smaller floods following lower antecedent flow conditions, at water temperatures of 18–20C, achieves the greatest spawning outcome for native fish. 4. Synthesis and applications. Our results indicate that principally temperature, and flow as a secondary variable, influence the timing and strength of fish spawning. The synthesis of these spawning relationships predicts that managers will achieve the greatest spawning return per unit of environmental water when flows are applied on top of an existing flow pulse. This study highlights the importance of considering a range of abiotic factors and the use of modelling scenarios to improve environmental flow outcomes.

Rapid increases in native riverine fish populations associated with trophic upsurge immediately following reservoir construction are well documented. Repeated upsurge periods and extended benefits to populations are, however, less understood. We used sclerochronology to investigate fish growth and netting surveys to estimate recruitment and abundance of a lacustrine population of an Australian riverine fish, the Macquarie perch (Macquaria australasica) in Lake Dartmouth. Record low inflows from 1997 to 2008 caused the reservoir to shrink to its lowest volume since construction. Refilling began in 2008, reaching 99% capacity in 2013. We hypothesized that fish growth, recruitment, and abundance would increase in response to the refilling of the lake, reproducing a similar response to the initial filling period. Our findings supported this hypothesis. Macquarie perch growth, recruitment, and abundance were enhanced during the refilling of Lake Dartmouth. Growth, best explained by the effects of dam height, change in dam height, temperature (and their interactions), and recruitment, were highest during the first years of refilling when lake levels and temperatures were low. We propose one or a combination of varying levels of intraspecific competition (low during initial filling and high following population expansion) and improved riverine conditions for reproductive success as the most plausible explanation. Our results suggest extended periods of low lake levels followed by rapid inundation events are likely to enhance recruitment and population growth opportunities for this species. While reservoir construction in general impacts negatively on native fish populations, the potential to offset these impacts for conservation management purposes should be considered.

Mark–recapture of fish is often used to inform fisheries or conservation management. Given that variability in tagging efficiencies can affect estimates of population size, it is important that rates of tag rejection are quantified. We double tagged over 45000 large-bodied, long-lived fish in a turbid lowland river in south-eastern Australia. During yearly recapture fish surveys, data on tag rejection were collected. We found that the probability of tag rejection varied as a function of fish species, tag type and tagger experience. Floy tags were more likely to be rejected as dart tags in large-bodied golden perch Macquaria ambigua (6 and 3% respectively), silver perch (18 and 4% respectively) and trout cod (19 and 7% respectively), whereas rates of rejection in the large-bodied Murray cod Maccullochella peelii were similar for both tag types (12 and 10% respectively). More experienced taggers had lower rates of rejection, which varied between 1 and 48% for individual taggers. We trialled three morphological locations for passive integrated transponder (PIT) tagging of fish, with rejection rates lowest for tags implanted in the stomach cavity and highest for those implanted in the pectoral musculature. This study presents the first tag rejection rates for dart, floy and PIT tags for lowland Australian river fish, information that can help guide future monitoring programs.

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.

While invasive fish management is heavily focussed on containment measures when introductions occur, examples from invasive species management in terrestrial systems suggest that there may also be considerable conservation benefits in implementing localized control programmes. We conducted a field-based experiment to assess the effectiveness of removing a globally significant invasive fish, eastern gambusia Gambusia holbrooki, from natural wetland habitats of south-eastern Australia. With recent work suggesting the impacts of eastern gambusia may be minimal for species with generalist life-history strategies, we hypothesized that the removal of eastern gambusia will reduce localized population growth of the invasive species, but will have little influence on the population growth of more generalist sympatric wetland fish species. We used a predictive modelling approach to investigate changes in eastern gambusia populations following removal activities, and how sympatric fish species responded to such changes. Although eastern gambusia rapidly populated habitats, we demonstrated that control actions substantially reduced the rate of population increase over the four-month study period. This suggests that control may be an effective localized strategy to suppress eastern gambusia densities. There was however, no evidence of any response to the removal actions by any of the three sympatric fish species investigated – carp gudgeon (Hypseleotris spp.), Australian smelt (Retropinna semoni) and the invasive common carp (Cyprinus carpio). These results support previous work which suggests that the flexible life-history strategies and behavioural traits of all three species allow co-existence with eastern gambusia. The study highlights the importance of understanding the potential outcomes of control options which is particularly pertinent for established aquatic invasive species where information on control effectiveness, population dynamics and/or ecosystem response is currently lacking.

Macquarie perch, Macquaria australasica Cuvier, is an endangered Australian freshwater fish that has historically supported popular recreational fisheries, but since the 1980s, it has experienced a decline in both distribution and abundance. This study investigated whether a marked decline in the population size of Macquarie perch has occurred at Lake Dartmouth between the mid-1980s and 2000 and the likelihood of the current legal minimum length (LML) of 350 mm TL protecting the population from recruitment overfishing. Recreational angler survey data showed strong evidence for a temporal population decline. Sampling of the population and construction of a simulation model indicated that the current LML would protect the population from recruitment overfishing. This study highlights the value of specifically investigating suspected threats to endangered fish populations to allow the instigation of effective fisheries management.

Summary 1. The biological productivity of floodplain rivers is intimately related to their flow regimes and it has been proposed that fish production should be linked to components of the flow regime in productivity models. To assess applicability of existing models of productivity in floodplain rivers, we tested predictions about growth during the early life stages of a common, short-lived fish (Australian smelt Retropinna semoni) in a non-flow-altered, temperate Australian floodplain river. 2. The morphometric condition of larval and juvenile fish measured over a five-year period was positively related to annual discharge, but the highest average seasonal growth rates occurred in two years of contrasting hydrology, one with early spring flooding and the other with predominantly low flows and a late season (within channel) flow pulse. 3. Analysis of daily growth measures indicated that timing, river height, the duration of in-channel flow events and antecedent flood events are all significant factors influencing the early growth of Australian smelt. The flexible manner in which fish growth responds to these factors appears to be an effective early life history strategy for a short-lived species occupying a highly variable environment. 4. Growth rates conformed to some predictions of the Flood Pulse Concept (in particular the Extended Flood Pulse Concept), but specific growth responses suggest that the Riverine Productivity Model and tenets of the Low Flow Recruitment Hypothesis best describe the production of Australian smelt in this system. We suggest that none of the existing conceptual models adequately describes fish productivity in temperate Australian floodplain rivers but that aspects of each are likely to be relevant under different flow conditions.

Summary 1. A common goal of many environmental flow regimes is to maintain and/or enhance the river’s native fish community by increasing the occurrence of successful spawning and recruitment events. However, our understanding of the flow requirements of the early life history of fish is often limited, and hence predicting their response to specific managed flow events is difficult. To overcome this uncertainty requires the use of adaptive management principles in the design, implementation, monitoring and adjustment of environmental flow regimes. 2. The Barmah-Millewa Forest, a large river red gum forest on the Murray River floodplain, south-east Australia, contains a wide variety of ephemeral and permanent aquatic habitats suitable for fish. Flow regulation of the Murray River has significantly altered the natural flood regime of the Forest. In an attempt to alleviate some of the effects of river regulation, the Forest’s water regime is highly managed using a variety of flow control structures and also receives targeted Environmental Water Allocations (EWA). In 2005, the largest environmental flow allocated to date in Australia was delivered at the Forest. 3. This study describes the adaptive management approach employed during the delivery of the 2005 EWA, which successfully achieved multiple ecological goals including enhanced native fish spawning and recruitment. Intensive monitoring of fish spawning and recruitment provided invaluable real-time and ongoing management input for optimising the delivery of environmental water to maximise ecological benefits at Barmah-Millewa Forest and other similar wetlands in the Murray-Darling Basin. 4. We discuss possible scenarios for the future application of environmental water and the need for environmental flow events and regimes to be conducted as rigorous, large-scale experiments within an adaptive management framework.

Summary With limited evidence linking Australia's Murray-Darling Basin fish species and flooding, this study assessed annual variation in abundance and recruitment levels of a small-bodied, threatened floodplain species, the Southern Pygmy Perch (Nannoperca australis), in floodplain habitats (creeks, lakes and wetlands) in the Barmah-Millewa Forest, Murray River, Australia. Spring and summer sampling over a 5-year period encompassed large hydrological variation, including 1 year of extended floodplain inundation which was largely driven by an environmental water release, and 2 years of severe regional drought. Recruitment and dispersal of Southern Pygmy Perch significantly increased during the floodplain inundation event compared with the other examined years. This study provides valuable support for an environmental water allocation benefiting a native species, and explores the link between flooding and its advantages to native fish. This suggests that the reduced flooding frequency and magnitude as a result of river regulation may well be a major contributing factor in the species’ decline in the Murray-Darling Basin.

Environmental flows aim to mimic components of a river's natural flow variability, including the magnitude, frequency, timing, duration, rate of change and the predictability of flow events. Aspects of the natural flow regime are thought to be linked to critical components of the life history strategies of many riverine fishes, including spawning and recruitment. In the Murray River, Australia, environmental flows are increasingly being used as a restoration tool; however, there is little information about the response of fish to these managed flow events. This study reports on the results from a 3-year study on the effects of water management on the spawning and recruitment of four native fish species in the mid-Murray River system. Two of these years were hydrologically similar, while the third year encompassed an extensive period of floodplain inundation, including the use of the largest environmental flow allocation to date in Australia. Drift nets were used to collect the drifting eggs and larvae of four iconic native species throughout their spawning season each year. Young-of-year were collected in the following autumn. Although golden perch and silver perch eggs were collected in all 3 years, both species increased their spawning activity during the major flood period compared to the previous two seasons. Murray cod and trout cod appeared not to increase their spawning activity in the flood year, but their recruitment may be increased when floodplain inundation occurs at times when their larvae and juveniles are present, most likely through the generation of abundant food resources. Whilst further study is required to confirm the role and mechanism of flooding in the spawning and recruitment of these species; this study provides important evidence of a link between the provision of an environmental flood and fish spawning and recruitment, and has significant implications for managing flows in regulated rivers. Copyright © 2008 John Wiley & Sons, Ltd.

– Relationships between fish length, otolith size, age and weight were assessed for a population of wild Australian smelt (Retropinna semoni) larvae and juveniles captured over a 4-year period to aid further interpretation of growth and condition during the early life history of the species. Nonlinear smoothed generalized additive models best described the fish–otolith size relationship during the larval and juvenile period, indicating that the proportionality between fish length and otolith size varies in relation to size. It is proposed that back-calculated predictions of fish size at a previous age or otolith size, accounting for individual variation is possible by assuming a body proportional hypothesis. Growth rate of larval and juvenile Australian smelt was best described using the Gompertz model that indicated a steady decline in growth rate after around 30 days of age. The allometric growth of larval and juvenile Australian smelt established from the length/weight relationship can subsequently be used to assess the condition of fish within this population using a relative condition or relative weight condition index. The results of the study have provided significant information to enable more precise growth reconstruction and condition assessment for the species in Australian lowland rivers.

To aid the interpretation of otolith microstructure in wild fishes, the present study assessed responses in daily otolith increment widths of early juvenile Australian smelt Retropinna semoni to sudden changes in feeding conditions. There was an almost immediate response in otolith increment widths (which can be interpreted as growth in length) to sudden changes in feeding conditions, with such changes being detected statistically after c. 4 days. Fish displayed compensatory growth when food supplies were increased following a period of limited food, indicating the magnitude of the response in growth appears highly dependant on feeding history. Additionally, fish size also appeared to influence increment widths suggesting that both fish size and feeding history are important factors that must be considered when interpreting otolith microstructure for the species.

– To aid otolith interpretation of wild fish, we conducted a laboratory study using metalarval Australian smelt (Retropinna semoni) collected from the Murray River, to examine daily increment deposition and the effects of different temperatures and feeding regimes on otolith growth. Daily increment deposition was confirmed by comparing the number of increments from an oxytetracycline mark with the known number of days from marking. After holding fish at two temperature levels and three feeding rates, both food density and temperature were found to have a significant effect on otolith growth, with food density having the greatest influence. Overall trends in final lengths and condition of fish were well represented by recent otolith growth. The results of the experiment have implications for estimating growth histories and its relationship to various environmental conditions.

Densities of silver perch Bidyanus bidyanus eggs drifting in the Murray River, Australia, suggested a peak spawning time between 2100 and 0100 hours, and a propensity to drift in higher densities near shore and at the bottom of the water column. The results highlight the need to consider such spatial and temporal patterns when estimating species-specific drift abundances.

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited., Genetic diversity underpins the ability of populations to persist and adapt to environmental changes. Substantial empirical data show that genetic diversity rapidly deteriorates in small and isolated populations due to genetic drift, leading to reduction in adaptive potential and fitness and increase in inbreeding. Assisted gene flow (e.g. via translocations) can reverse these trends, but lack of data on fitness loss and fear of impairing population “uniqueness” often prevents managers from acting. Here, we use population genetic and riverscape genetic analyses and simulations to explore the consequences of extensive habitat loss and fragmentation on population genetic diversity and future population trajectories of an endangered Australian freshwater fish, Macquarie perch Macquaria australasica. Using guidelines to assess the risk of outbreeding depression under admixture, we develop recommendations for population management, identify populations requiring genetic rescue and/or genetic restoration and potential donor sources. We found that most remaining populations of Macquarie perch have low genetic diversity, and effective population sizes below the threshold required to retain adaptive potential. Our simulations showed that under management inaction, smaller populations of Macquarie perch will face inbreeding depression within a few decades, but regular small-scale translocations will rapidly rescue populations from inbreeding depression and increase adaptive potential through genetic restoration. Despite the lack of data on fitness loss, based on our genetic data for Macquarie perch populations, simulations and empirical results from other systems, we recommend regular and frequent translocations among remnant populations within catchments. These translocations will emulate the effect of historical gene flow and improve population persistence through decrease in demographic and genetic stochasticity. Increasing population genetic connectivity within each catchment will help to maintain large effective population sizes and maximize species adaptive potential. The approach proposed here could be readily applicable to genetic management of other threatened species to improve their adaptive potential.

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.Investigations into the feeding of the early stages of fishes can provide insights into processes influencing recruitment. In this study, we examined ontogenetic changes in morphology and feeding behaviour of two native Australian freshwater species, Murray cod, Maccullochella peelii peelii, and golden perch, Macquaria ambigua, and the alien species, common carp, Cyprinus carpio. Murray cod free embryos are large and well developed at the onset of feeding, whereas the other two species begin exogenous feeding much younger and are smaller and less-developed. Carp commence exogenous feeding 3 days earlier than golden perch, and show more advanced development of the eyes and ingestive apparatus. We conducted feeding experiments, presenting larvae of the three species with a standardised prey mix (comprising equal numbers of small calanoid copepods, large calanoid copepods, small Daphnia, and large Daphnia). Larvae of most tested ages and species showed a preference for mid-sized prey (300-500 µm wide). This was true even when their gapes substantially exceeded the largest prey offered. Daphnia were consumed more than similar-sized copepods. The results of this study suggest that survival through their larval period will be threatened in all three species if catchable prey < 500 µm in width are not available throughout such time. They also suggest that interspecific competition for prey may occur, especially when larvae are very young. The precocious development of structures involved in feeding and the extended transition from endogenous to exogenous feeding of early carp larvae are likely to have contributed to the success of this species since its introduction to Australia.

Highly variable recruitment is common for many riverine fish species, governed by a wide range of biotic and abiotic drivers that operate at local and regional scales. The dynamics and drivers of recruitment for many Australian freshwater fish species, particularly those that are rare and long-lived, are relatively undescribed. This study describes the recruitment dynamics of an endangered riverine fish, Macquarie perch Macquaria australasica, across five isolated populations from south-eastern Australia, and relates these dynamics to drivers that vary at local and regional scales. We hypothesised large flow events occurring during the core egg and larval period would be negatively associated with recruitment strength and that recruitment patterns across populations would fluctuate in synchrony in response to extremes in river discharge resulting from regional-scale climatic patterns. Discharge during the core egg and larval period, which was highly correlated across the region; and a local scale variable, spawning stock abundance, were the covariates most important in explaining recruitment strength. We also observed synchronised patterns in recruitment across our populations, thus conforming to predictions of the Moran effect (environmental synchrony). The findings suggest most remnant populations of Macquarie perch, which are now predominantly isolated within small tributary systems characterised by highly variable flows, face a heightened risk of poor recruitment periods, particularly under climate change predictions. The synchronised patterns in recruitment suggests threatened freshwater fishes like Macquarie perch with highly fragmented isolated populations, have an increased risk of the regional population becoming imperilled, thus, the need for a coordinated multijurisdictional conservation approach.