A protected flow breaks the drought for golden perch (Macquaria ambigua) spawning along an extensive semi‐arid river system

ABSTRACTFish population dynamics are influenced by intrinsic and environmental drivers across multiple spatial and temporal scales. A thorough understanding of these drivers is essential for maintaining fish recruitment in flow‐regulated rivers. In the Murray–Darling Basin (MDB) in Australia, golden perch (Macquaria ambigua) are an iconic species with a life history characterised by irregular, strong recruitment of year classes. In‐channel flow pulses and overbank flows are important for spawning and recruitment; however, the drivers of fluctuations in golden perch recruitment have not been sufficiently quantified to allow for full operationalisation into river and fishery management. We used long‐term standardised electrofishing data to model relationships between the relative abundance of young‐of‐the‐year (YOY) golden perch with large‐scale climate indices, local river hydrology and temperature, and river/fishery management actions. While consistent recruitment was observed in only five rivers, there were strong, positive associations between the abundance of YOY golden perch and two broadscale climatic drivers (Australian Monsoonal Index and total rainfall across the northern MDB). The driver of these relationships is likely to be the effects of climate on local river discharge and temperature. YOY abundance increased with temperature and generally increased with river discharge to an optimum before declining at a very high discharge. We also found positive but variable effects of stocking, suggesting that stocking of fish can augment natural populations but that outcomes are spatially and temporally inconsistent. Our results have the potential to enable proactive management targeted towards supporting the hydrological conditions necessary for self‐sustaining golden perch populations.

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.

Context Dryland rivers are unique ecosystems, where drought and flood play an important role in shaping the ecosystem. River regulation has altered the natural flow regime in many of these systems, affecting migration cues and connectivity for many species. Aims To quantify the discharge-related movements of Murray cod and golden perch within the Condamine–Balonne River subject to differing levels of river regulation. Methods We quantified flow regime variability, river regulation and fish movement to develop generalised additive mixed models to predict movement probability for Murray cod and golden perch. Results Both species showed strong positive relationships between discharge and movement. Murray cod did not show any association with river regulation; however, medium-sized individuals were significantly more likely to move than were smaller or larger fish. Golden perch movements varied among levels of regulation, were more likely to move as body weight increased and showed seasonality of movement, moving less during winter. Conclusions This study presents the largely unobserved movement behaviours of fish across a gradient of river regulation and environmental conditions in the northern Murray–Darling Basin. Implications This information is valuable for informing policy and management decisions that may affect species’ life-history requirements in analogous river systems.

Larval silver perch (Bidyanus bidyanus) and golden perch (Macquaria ambigua) were subjected to gradients of light, depth, flow and wood leachate from river red gum (Eucalyptus camaldulensis) as well as a control treatment with no gradient. Both species were strongly attracted to light, while golden perch larvae were also attracted to river red gum and were carried downstream by water flow. Neither species displayed any response to depth. Gradient responses of silver perch were significantly more variable (P < 0.05) than those of golden perch, which may result in silver perch larvae being more widely distributed in floodplain habitats. Golden perch larvae may be more closely associated with inundated river red gum than silver perch larvae.

ABSTRACTManaging fish populations in regulated rivers requires an understanding of the spatial and temporal scale of their dispersal, the locations of key spawning and nursery habitats and the hydraulic processes that interplay with their life history. Golden perch (Macquaria ambigua), an Australian freshwater pelagic‐spawning fish, highlights the worldwide challenges of managing riverine species that rely on hydraulic conditions to sustain critical metapopulation processes. This study aimed to quantify the spatial scale of early life history golden perch dispersal after a drought‐breaking in‐channel flow event in early 2020 in a regulated lowland river. Otolith microchemistry (87Sr/86Sr) and single nucleotide polymorphisms (SNPs) determined natal origins and sibling relationships, respectively, of young‐of‐year (YOY) caught in a floodplain nursery with larval fish captured upstream. For fish collected in the floodplain nursery, dispersal distances ranged to ~1600 km. Otolith microchemistry attributed 52% of YOY as localised in origin, 44% as originating in the midcatchment and 4% from the most upstream sample locations. Genetic analyses identified a full‐sibling pair captured 900 km apart and 31 half‐sibling pairs that linked YOY to larval fish captured at a diversity of upstream sites. Our study highlights the range of spatial scales over which ELH dispersal can occur for golden perch and emphasises the importance of interconnected flowing river habitats in sustaining metapopulation processes. We illustrate the positive results that increased riverine connectivity can yield for fish with similar life history strategies.

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 × 10–6L3.12). Our data suggest that the MDB can be treated as one management unit in terms of golden perch maximum size, growth and mortality parameters.

A 2 year (2000–2001) radio‐tagging study was undertaken to investigate the movements of 51 golden perch Macquaria ambigua in the Murray River at Nyah in north‐western Victoria, Australia. During the winter of both years, golden perch did not undertake movements >5 km and displayed strong home range fidelity. In the first year of the study there was an increase in the distance of golden perch movement during late spring which coincided with increasing water temperature and river discharge. Nineteen golden perch were tracked during this period, of which 10 travelled downstream between 11 and 290 km. Seven of these fish moved to an area below the junction of the Murray and Wakool Rivers. Five golden perch travelled upstream between 13 and 35 km, four of which travelled to an area around the junction of the Murray River and Speewa Creek. The remaining four golden perch undertook localized movements of <5 km. Many of the long distance movements undertaken in spring 2000 were rapid and 53% of these golden perch returned to within 3 km of their release locations, indicating homing behaviour. Given that the rapid movements of golden perch in spring coincided with the known spawning season of this species, these long distance movements may be associated with reproductive strategy.

The micro‐increments in otoliths from a series of golden perch (Macquaria ambigua) larvae of up to 15 days known age (n = 124, total length (TL) 4.14 to 10.0 mm) were examined and counted to establish the age at formation of the first increment, and periodicity of formation of subsequent increments. The regression of true age on increment count (true age = 3.54 +1.36 × increment count) was significant (r2 = 0.78, P < 0.001) and the slope of the overall regression (1.36 day–1) was not significantly different to 1 (t = 0.09, P = 0.05). First increment formation occurred from day 3 in some larvae, and was completed by day 13 in all larvae. A median estimate for age at first‐increment deposition was 6.0 days, when 50% of the daily sample (n = 10 fish) had at least one increment. However, solving the regression for age when increment number equaled 1.0 provided an estimate of mean age at first‐increment deposition of 4.9 days. Our study validated daily growth increment deposition for golden perch larvae over the first 15 days of development and cautions that age at first‐increment formation varied within a single cohort of larvae by 10 days (i.e., youngest larvae 3 days, oldest larvae 13 days old).

Migratory fish species are highly vulnerable to stream fragmentation. Potamodromous golden perch (Macquaria ambigua) inhabit the barrier-laden Murray–Darling Basin (MDB), Australia’s largest river system, and its lifecycle includes a requirement for uninterrupted stretches of flowing water habitat. Owing to these barriers, large-scale connectivity in many regions is limited to periods of high flow events that facilitate barrier drown-out. We undertook a 3-year (2021–2024) study using telemetry to quantify the movements of 150 adult golden perch from the Barwon–Darling River over a period that encompassed numerous high flow events and flooding. Approximately 75% of tagged golden perch undertook movements &gt; 50 km, with &gt; 90% of movements in an upstream direction, extending up to 1500 km and associated with increased river discharge. Tributary entries were detected on multiple occasions, with an apparent preference for specific tributaries. Ten fish migrated &gt; 1000 km upstream across multiple flow events. The results of this study (1) highlight the importance of the Barwon–Darling River and tributaries as a key migration conduit for adult golden perch, (2) demonstrate that multiple flow events are required to achieve large-scale dispersal and (3) provide quantitative flow-movement relationships that can be used to support inter-regional management actions. These management actions might include barrier removal, the construction of fishways and protection of tributary–mainstem flow events.

For riverine fishes threatened by fragmentation and flow modification, effective management requires an understanding of when and where key life history processes (spawning, recruitment and movement) take place. The structural and chemical properties of otoliths provide a unique means to recount a fish’s life in time and space. We investigated the age structure of the migratory, pelagic-spawning golden perch (Macquaria ambigua) in the Murray River, Australia, and used water and otolith 87Sr/86Sr ratios to delineate the natal origin and movement of fish from discrete cohorts. Water 87Sr/86Sr was distinct among the Darling River (a major tributary) and lower and mid-Murray River. Otolith chemistry revealed golden perch collected in the lower Murray River were progeny of spawning in either the Murray or Darling rivers, during years characterised by within-channel rises in flow, or in both rivers in a year of overbank flooding. Movement of juvenile fish from the Darling River substantially influenced population structure in the lower Murray River, whereby post-flood population growth was largely due to the immigration of age-1+ fish. This study demonstrates the potential importance of tributary recruitment sources, dispersal and connectivity on main-stem population dynamics and the utility of otolith chemistry for spatially reconciling population structure and the life histories of freshwater fishes.

Context Intermittent rivers make up more than 50% of the world’s rivers. Refuge waterholes in these systems are critical for survival of fish populations. Aim This study investigated the effect that angling pressure imparts on native fish within refuge waterholes. Methods Golden perch (Macquaria ambigua) size structure was analysed in eight refuge waterholes across three catchments of the northern Murray–Darling Basin. Waterhole characteristics were recorded, with town proximity or remoteness being adopted as a surrogate variable for angling pressure. Key results Remoteness was found to be significantly correlated with median length, biomass, and proportion of legal-sized fish, but not with fish density. Sampling occurred after widespread connective flows, and the strength of remoteness as a predictor of median length suggests that redistribution of legal-sized golden perch on these flows was minimal. Legal-sized fish were poorly represented in the length–frequency distributions of near-town waterholes, and smaller size classes were well represented in most waterholes. Conclusion This study suggests that populations of golden perch in refuge waterholes near towns face significant angling pressure, with impacts on size structure at a local level. Implications These findings may have wider implications for the long-term resilience of the species.

Larval golden perch, Macquaria ambigua, and silver perch, Bidyanus bidyanus, were exposed to light gradients in wavebands centred on 400, 496, 601 and 695 nm at nominal quantum irradiance values of 0–1, 1–0 and 10 μmol m−2 s−l. Silver perch larvae displayed stronger phototactic behaviour than golden perch, and both species were most responsive to light in the 601 nm waveband. The intensity of phototactic responses in both species was greater at higher irradiance levels. Enhanced responsiveness to longer wavelengths reflects possible adaptations to life in turbid habitats where the underwater light field is dominated by yellow/orange wavebands.At night, traps fitted with 12 h yellow lightsticks attracted more golden perch larvae than traps with blue, green, orange, red or no lightstick. The efficacy of yellow lightsticks may be due to yellow/orange wavebands not being attenuated under water as rapidly as blue or red wavebands. Yellow lightsticks also emit a greater intensity of light over a longer time than other colours tested, which may have increased the effectiveness of yellow traps. Light traps were ineffective during the day.

Primary and secondary stress responses in golden perch, Macquaria ambigua

SummaryDegradation of instream habitats in the northern Murray–Darling Basin has occurred through numerous stressors, including siltation, clearing of bankside vegetation, intrusion of livestock and impacts of pest species. A better understanding of habitat preferences of native fish species could help guide future instream habitat restoration actions. The habitat choices of seven native fish species, juvenile Murray Cod (Maccullochella peelii), juvenile Golden Perch (Macquaria ambigua ambigua), juvenile Silver Perch (Bidyanus bidyanus), adult Murray–Darling Rainbowfish (Melanotaenia fluviatilis), adult Olive Perchlet (Ambassis agassizii), adult Un‐specked Hardyhead (Craterocephalus stercusmuscarum fulvus) and adult carp gudgeons (Hypseleotris spp.) were tested in preference troughs to help inform potential habitat restoration actions in the Condamine catchment. Each species was given a choice between pair combinations of open sandy habitat, submerged macrophytes, emergent plants and rocky rubble. Habitat preferences varied between species. Murray Cod, Golden Perch, carp gudgeons and Olive Perchlets preferred structure over open sandy habitat, whilst juvenile Silver Perch, Un‐specked Hardyhead and Murray–Darling Rainbowfish did not avoid open sandy habitats. Juvenile Murray Cod preferred rocky rubble habitat over all other habitat choices. Use of complex rock piles to provide nursery habitat for Murray Cod populations is a potential restoration option. Introduction of rock could also benefit Golden Perch and carp gudgeons. Use of emergent plants, submerged macrophytes and rocky rubble for habitat restoration all appear to have merit for one or more species of small‐bodied fishes or juvenile stages of larger sized fishes. Rocky rubble or floating attached macrophytes could be viable restoration options in areas too turbid to establish submerged macrophytes. These habitat interventions would complement existing actions such as re‐snagging and provision of fish passage to assist with sustainable management of native fish populations.

Experiments were conducted over four consecutive breeding seasons. Golden perch, Macquaria ambigua, larvae (total length, 5.0 mm) held at 23º to 25ºC, commenced feeding on crustacean zooplankton (&amp;lt;350 pm in length) five days after hatching, at age D6 (D1 = day of hatch). Zooplankton density had a significant effect (P &amp;lt; 0.01) on the survival of larvae in 70-L aquaria. A delay of only two days to age D8 in initial feeding significantly reduced (P &amp;lt; 0.01) survival, and larvae not offered zooplankton until D10 did not commence feeding. There was a positive linear relationship (r2 = 0.98) between survival in earthen ponds (0-57.6%) and the volume of small zooplankton sampled from the ponds at stocking, but survival was not affected by larval stocking density (32-365 m-2) or length of the culture period (28-53 days). A mean survival of 44.6% in ponds that were left dry over winter and then stocked 10-14 days after filling, was significantly higher (P &amp;lt; 0.01) than survival in ponds stocked only 2-5 days after filling or in ponds inundated during winter. Survival, growth and production were not significantly different among ponds fertilized with inorganic fertilizer (NPK) alone or in combination with lucerne hay or poultry manure. Larvae grew at rates of 0.5-1.1 mm day-1, production rates were up to 153 kg ha-1 and a maximum number of 271 000 juveniles were reared in a 0.3 ha pond. Approximately 3 × 106 golden perch are produced annually at hatcheries in eastern Australia using techniques developed during this study.