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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]

Abstract Considerable technical developments over the past half century have enabled widespread application of electronic tags to the study of animals in the wild, including in freshwater environments. We review the constraints associated with freshwater telemetry and biologging and the technical developments relevant to their use. Technical constraints for tracking animals are often influenced by the characteristics of the animals being studied and the environment they inhabit. Collectively, they influence which and how technologies can be used and their relative effectiveness. Although radio telemetry has historically been the most commonly used technology in freshwater, passive integrated transponder (PIT) technology, acoustic telemetry and biologgers are becoming more popular. Most telemetry studies have focused on fish, although an increasing number have focused on other taxa, such as turtles, crustaceans and molluscs. Key technical developments for freshwater systems include: miniaturization of tags for tracking small-size life stages and species, fixed stations and coded tags for tracking large samples of animals over long distances and large temporal scales, inexpensive PIT systems that enable mass tagging to yield population- and community-level relevant sample sizes, incorporation of sensors into electronic tags, validation of tag attachment procedures with a focus on maintaining animal welfare, incorporation of different techniques (for example, genetics, stable isotopes) and peripheral technologies (for example, geographic information systems, hydroacoustics), development of novel analytical techniques, and extensive international collaboration. Innovations are still needed in tag miniaturization, data analysis and visualization, and in tracking animals over larger spatial scales (for example, pelagic areas of lakes) and in challenging environments (for example, large dynamic floodplain systems, under ice). There seems to be a particular need for adapting various global positioning system and satellite tagging approaches to freshwater. Electronic tagging provides a mechanism to collect detailed information from imperilled animals and species that have no direct economic value. Current and future advances will continue to improve our knowledge of the natural history of aquatic animals and ecological processes in freshwater ecosystems while facilitating evidence-based resource management and conservation.

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]

Understanding the spatial and temporal scales over which key population processes occur is fundamental to effective fisheries management, especially when informing recovery actions following extreme events. In 2018–19, hypoxia-induced fish kills occurred in the lower Darling River, south-eastern Australia. We collected carcasses of three potamodromous species that perished during these events to reconstruct their lifetime movements and identify potential recovery mechanisms. Golden perch Macquaria ambigua , Murray cod Maccullochella peelii and silver perch Bidyanus bidyanus otolith 87Sr/86Sr profiles were compared with water 87Sr/86Sr ratios to better understand natal provenance and movement history, and to identify the scale at which migration influences population processes. Golden perch were predominantly locally spawned (Darling River), although we found some evidence of emigration into the nearby Murray River early in life and return movements into the Darling River. Murray cod were mainly locally spawned and thereafter lifelong residents, with some evidence of stocking supplementing populations. Silver perch were mostly immigrants, with the Murray River (>500 km away) the principal source of fish. For recovery of native fish populations to be effective in the Darling River, recovery actions are required that incorporate knowledge on the relevant spatial and temporal scales over which life history processes occur. Otoliths were used to retrospectively determine lifetime movements of golden perch, Murray cod and silver perch that died in fish kills in the lower Darling River in 2018–19. Movement between the Murray and Darling rivers appears important for population function of golden perch and silver perch, but not Murray cod, emphasising the need for complementary local and regional-scale recovery efforts. [ABSTRACT FROM AUTHOR]