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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.

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.

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.