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Seeking out appropriate habitat or food resources is one of the key reasons why animals move. Despite the benefits of movement, some individuals in a population remain resident or express alternative movement phenotypes. Movement, however, is energetically costly and can result in resources being diverted away from growth and reproduction. The presence of multiple movement phenotypes within populations suggests that each can have commensurate levels of performance depending on the underlying environmental conditions.Here we explore the context‐dependent costs and benefits of upstream and downstream juvenile dispersal in a large river system. We expect that if the energetic costs of moving (upstream against a current or downstream with a current) exceed any benefits to growth, then residents (who do not move) will have faster growth. Alternatively, movement costs may be offset if individuals move to more favourable environments, resulting in dispersers benefiting with faster growth.We used biological information naturally archived in the otoliths of a potamodromous fish, golden perch Macquaria ambigua, to quantify how movement phenotypes affect growth across individuals exposed to spatiotemporally varying environmental conditions.We found that juvenile growth differed considerably among dispersal phenotypes (resident, upstream, downstream, stocked): in general, surviving wild‐spawned downstream and upstream dispersers and hatchery‐stocked fish all grew faster than individuals that remained resident within their natal reach. Further, juvenile growth was sensitive to local environmental conditions and had carryover effects from an individual's natal‐year. Juvenile growth of all dispersal phenotypes was higher in years with below average natal‐year summer discharge (when fish are ~2–3 months old), likely because of increased concentrations of food resources. In contrast, the effects of natal‐year spring discharge (around the time individuals were spawned) were dependent on dispersal direction, with positive effects for downstream dispersers and upstream dispersers, and negative effects for resident individuals.Our results suggest that an individual's growth can benefit from early‐life movement, although the magnitude of this effect depends on local environmental conditions and the direction travelled. Our study reinforces the importance of heterogeneous and connected riverscapes that foster a diversity of individual growth responses. [ABSTRACT FROM AUTHOR]

Context: Understanding the movement behaviour of flow-dependent fish species is a foundational principle underlying the effective management of highly modified riverscapes. Aims: To determine how variations in river discharge and instream barriers affect the residency, survival and movement of golden perch (Macquaria ambigua) in the degraded Gwydir River system within the northern Murray–Darling Basin. Methods: We monitored the movement of 25 acoustic-tagged golden perch for up to 3 years by using a linear array spanning ~180 km of the main river channels across the lower Gwydir system. Key results: Golden perch were largely sedentary for extended periods, with movements constrained by the barrier maze that now defines the system. High flows facilitated passage over instream barriers, with the highest periods of activity occurring in spring and early summer, and to a lesser extent in autumn. Conclusion: Our findings are indicative of a highly constrained and isolated population of golden perch that is now likely to be neither a source nor a sink, but is in effect a false sink perpetuated by re-stocking practices. Implications: The rehabilitation of the fish community in the Gwydir and other systems in similarly poor condition throughout the Murray–Darling Basin will require major institutional and societal change. We tracked golden perch in the highly modified Gwydir River to understand their response to different flows and the effect of barriers. Normally considered highly mobile, we found our golden perch to be highly constrained and largely sedentary, with little apparent connection to the wider population. The recovery and restoration of golden perch in the Murray–Darling Basin will require societal change. This article belongs to the collection Environmental flows in northern Murray–Darling Basin: what we know about the science and management after a decade of practice. [ABSTRACT FROM AUTHOR]

Anthropogenic threats such as water infrastructure, land-use changes, overexploitation of fishes and other biological resources, invasive species and climate change present formidable challenges to freshwater biodiversity. Historically, management of fish and fishery species has largely been based on studies of population- and community-level dynamics; however, the emerging field of conservation physiology promotes the assessment of individual fish health as a key management tool. Fish health is highly sensitive to environmental disturbances and is also a fundamental driver of fitness, with implications for population dynamics such as recruitment and resilience. However, the mechanistic links between particular anthropogenic disturbances and changes in fish health, or impact pathways, are diverse and complex. The diversity of ways in which fish health can be measured also presents a challenge for researchers deciding on methods to employ in studies seeking to understand the impact of these threats. In this review, we aim to provide an understanding of the pathway through which anthropogenic threats in freshwater ecosystems impact fish health and the ways in which fish health components impacted by anthropogenic threats can be assessed. We employ a quantitative systematic approach to a corpus of papers related to fish health in freshwater and utilize a framework that summarizes the impact pathway of anthropogenic threats through environmental alterations and impact mechanisms that cause a response in fish health. We found that land-use changes were the most prolific anthropogenic threat, with a range of different health metrics being suitable for assessing the impact of this threat. Almost all anthropogenic threats impacted fish health through two or more impact pathways. A robust understanding of the impact pathways of anthropogenic threats and the fish health metrics that are sensitive to these threats is crucial for fisheries managers seeking to undertake targeted management of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Variation in river flow is a strong behavioural determinant for the movement of many freshwater fish species and often is linked to key aspects of their life cycle. The alteration of natural flow regimes to meet human water demands can result in changes to this variability, and cause declines in water‐dependent biota. Environmental flows are used as a remediation tool in some regulated rivers with the intention of restoring aspects of the natural flow regime to benefit riverine species, although empirical data are required to inform the efficacy of these interventions.Using acoustic telemetry, we quantified the movement responses of two large‐bodied native fish species (freshwater catfish, Tandanus tandanus and Murray cod, Maccullochella peelii) to variations in river flow over 4 years in two intermittent regulated rivers in the northern Murray–Darling Basin, Australia. Both rivers received periodic environmental flow releases and also there were several large natural flow events during the study period.Both species displayed a range of intra‐specific movement behaviours. Analysis of individuals' movements revealed five distinct functional groups, which were represented in both species. We found that periods of environmental flow delivery played an important role in the movement behaviour of both species. Murray cod were more likely to move during periods of environmental flow releases, whereas freshwater catfish were less likely to move on an environmental release following higher antecedent flows.No large‐scale philopatric movements were observed, yet Murray cod were more likely to move during the breeding period, indicative of nest site selection. We also found that the likelihood of movement in both species was higher in the smaller of the two rivers for a given magnitude of flow.Our results suggest that environmental flows may benefit certain fish species by facilitating, rather than cueing breeding behaviours, allowing individuals improved access to, and provision of, higher‐quality nesting habitats.These findings will aid water managers in creating economical and targeted environmental flow releases, timing larger flow pulses for the species with flow‐cued reproductive strategies, and providing a continuity of smaller baseflows for species whose reproduction is not dependent on flow cues but may be enhanced by greater connectivity. [ABSTRACT FROM AUTHOR]

Translocation of individuals is a widely used tool in the conservation of threatened species. The movement behaviours of translocated individuals in their new environment are a key factor that can influence translocation success (i.e. survival and reproduction). In this study, eel‐tailed catfish (Tandanus tandanus) and Murray cod (Maccullochella peelii) movements were monitored using fine‐scale acoustic telemetry over a 5‐month period in two lowland rivers in eastern Australia. Fine‐scale movement and habitat selection were compared among translocated lacustrine and resident riverine T. tandanus and between species. We found no difference in fine‐scale movement behaviours between translocated and resident T. tandanus; however, there was some variation in movement response to environmental variation between species. In contrast, habitat selection varied not only between the two species, but also between resident and translocated T. tandanus individuals. Notably, activity was significantly lower in the first day after release compared to the remainder of the study period. Although T. tandanus translocated from a reservoir had never experienced the environmental fluctuations of a riverine system, individuals still responded in the same way as resident riverine fish, suggesting an innate behavioural response. However, this was not the case for habitat selection, where translocated individuals preferred habitats more common in their source population's lacustrine environment. The findings of this study are important in guiding future conservation efforts involving the translocation of wild‐caught fish, primarily the importance of the suitable habitat at the release site to ensure the success and persistence of translocated populations. [ABSTRACT FROM AUTHOR]

This study examines the complex diadromous movements in pinkeye mullet (Trachystoma petardi) of south-eastern Australia. The techniques used to study these movements included LA-ICP-MS single line ablation transects and microchemical imaging as well as preliminary acoustic telemetry results which were used to aid in interpretation of chemical signatures related to complex movement patterns across salinity gradients. Ba:Ca and Sr:Ca from single ablation transects and microchemical images revealed differences between the otolith core and outer regions. Otolith Ba:Ca and Sr:Ca patterns were more easily distinguished in images compared to transects and these revealed that T. petardi spend their early life in saline waters. Movement patterns for adults varied, with a range of movements identified between fresh and saline waters. Telemetry data assisted in explaining the likely cause of the ambiguity in otolith microchemistry data, including identification of multiple rapid movements across salinity gradients. However, many movements through salinity gradients appear too brief to result in any clear Sr:Ca or Ba:Ca saline or mesohaline signature within the chemistry of the otolith. The combination of otolith chemistry and telemetry proved useful in providing information on this poorly understood species suggesting that T. petardi display a catadromous life history. [ABSTRACT FROM AUTHOR]

Localized catastrophic events can dramatically affect fish populations. Management interventions, such as stocking, are often undertaken to re-establish populations that have experienced such events. Evaluations of the effectiveness of these interventions are required to inform future management actions. Multiple hypoxic blackwater events in 2010-2011 substantially reduced fish communities in the Edward-Wakool river system in the southern Murray-Darling Basin, New South Wales, Australia. These events led to extensive fish kills across large sections of the entire system following a period of prolonged drought. To expedite recovery efforts, 119 661 golden perch Macquaria ambigua and 59 088 Murray cod Maccullochella peelii fingerlings were stocked at five locations over 3 years. All fish stocked were chemically marked with calcein to enable retrospective evaluation of wild or hatchery origin. Targeted collections were undertaken 3 years post-stocking to investigate the relative contribution of stocking efforts and recovery via natural recruitment in the system. Of the golden perch retained for annual ageing (n = 93) only nine were of an age that could have coincided with stocking activities. Of those, six were stocked. The dominant year-class of golden perch were spawned in 2009; before the stocking programme began and prior to blackwater events. All Murray cod retained (n = 136) were of an age that coincided with stocking activities, although only eight were stocked. Among the Murray cod captured, the dominant year-class was spawned in 2011, after the blackwater events occurred. The results from this study provide first evidence that natural spawning and recruitment, and possibly immigration, were the main drivers of golden perch and Murray cod recovery following catastrophic fish kills. Interpreted in the context of other recent examples, the collective results indicate limited benefit of stocking to existing connected populations already naturally recruiting in riverine systems. [ABSTRACT FROM AUTHOR]

- Understanding the larval ecology of individual fish species is fundamental in ensuring their long-term conservation. The endangered eastern freshwater cod, Maccullochella ikei, is endemic to the Clarence and Richmond River systems of north-eastern New South Wales, Australia. Little is known about the behaviour of larval M. ikei in the wild, particularly before and after the swim-up stage, and following dispersal from the nest site. The aims of this study were to quantify the swimming ability, depth selection, light preference and substrate selection of hatchling to day-30 M. ikei under controlled laboratory conditions, and to describe its growth and development over the same period. Maccullochella ikei larvae grew constantly but not consistently during the experiment. Exogenous feeding commenced around day 12, prior to the full exhaustion of the yolk. Maximal swimming ability improved daily, but maximum swimming speed declined significantly between days 12 and 13 and remained low. Maccullochella ikei larvae were initially photonegative but were positively phototactic by day 10. Depth selection was for the benthos until day 8, beyond which time larvae dispersed to all depths when released. Substrate selection was for sand in younger larvae but changed to upstream substrates as the experiment progressed. The results of the current study suggest that the period between day 10 and day 20 is critical in the early ontogeny of M. ikei, when it switched phototrophic behaviour, transitioned from endogenous to exogenous feeding and experienced a decline in swimming ability. [ABSTRACT FROM AUTHOR]