Comparative movements of four large fish species in a lowland river

Quantifying movement of multiple threatened species to inform adaptive management of environmental flows

There is a growing need for water managers to refine and optimise environmental flow strategies (e-flows) to balance water requirements for humans and nature. With increasing demands for freshwater and consequent declines in biodiversity, managers are faced with the problem of how to adaptively manage e-flows for multiple stakeholders and species whose flow requirements may overlap or vary. This study assessed the effectiveness of a regulated e-flow release strategy from a dam, aimed at providing movement opportunities and facilitating reproductive processes for multiple threatened species. Movements of 24 Mary River cod (Maccullochella mariensis), 20 Australian lungfish (Neoceratodus forsteri) and 13 Mary River turtle (Elusor macrurus) were quantified using acoustic telemetry over a three-year period. The influence of regulated e-flow releases, season, river depth, water temperature and rainfall on animal movements was assessed using Generalised linear mixed models (GLMMs). Models showed that hydraulic connectivity provided by both natural flows and regulated e-flow releases facilitated movement of all three species between pool habitats, throughout the year. Mary River turtles made extensive use of regulated e-flow releases when moving between habitats, whereas Mary River cod and Australian lungfish required additional natural rises in river height above the regulated e-flows to trigger movements. Significant movement activity was also recorded for cod and turtles during the dry season (winter and spring), broadly coinciding with breeding periods for these species. The effectiveness of, and potential improvements to, current e-flow strategies to sustain key life-history requirements of these species is discussed. Findings suggest a revised e-flow strategy with relatively minor increases in the magnitude of e-flow releases throughout winter and spring, would be effective in providing movement opportunities and supporting reproductive success for all three species. This study demonstrates that by quantifying movement behaviour in an e-flow context, ecological risk assessment frameworks can then be used to assess and provide for critical life-history requirements of multiple species within the context of a highly regulated system under increasing water use demands.

Lifetime movement history is associated with variable growth of a potamodromous freshwater fish

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.

Multi-year pair-bonding in Murray cod (Maccullochella peelii)

Mating strategies in fishes are known to include polygyny, polyandry and monogamy and provide valuable insights regarding powerful evolutionary forces such as sexual selection. Monogamy is a complex of mating systems that has been relatively neglected. Previous work on mating strategies in fishes has often been based on observation and focused on marine species rather than freshwater fishes. SNPs are increasingly being used as a molecular ecology tool in non-model organisms, and methods of probabilistic genetic analysis of such datasets are becoming available for use in the absence of parental genotypes. This approach can be used to infer mating strategies. The long-term pair bonding seen in mammals, reptiles and birds has not been recorded in freshwater fishes-in every other respect an extremely diverse group. This study shows that multi-year pair bonding occurs in an Australian Percichthyid fish that exhibits paternal care of eggs and larvae. Using SNPs, full sibling pairs of larvae were found over multiple years in a three-year study. Stable isotope signatures of the larvae support the genetic inference that full sibling pairs shared a common mother, the ultimate source of that isotopic signature during oogenesis. Spatial and temporal clustering also suggests that the full sibling larvae are unlikely to be false positive identifications of the probabilistic identification of siblings. For the first time, we show multi-year pair bonding in a wild freshwater fish. This will have important conservation and management implications for the species. This approach could provide insights into many behavioural, ecological and evolutionary questions, particularly if this is not a unique case. Our findings are likely to initiate interest in seeking more examples of monogamy and alternative mating strategies in freshwater fishes, particularly if others improve methods of analysis of SNP data for identification of siblings in the absence of parental genotypes.

Site Fidelity, Habitat Use, and Movement Patterns of the Common Carp during Its Breeding Season in the Pearl River as Determined by Acoustic Telemetry

Understanding fish migration patterns and habitat use is essential for fisheries management. We conducted an acoustic fine-scale tracking experiment from March to June 2017 to determine the common carp movement pattern and habitat use in the downstream area of the Pearl River. The eight tagged common carp were detected for 39.38 ± 29.57 d, on average, with a total average detection period of 42.12 ± 28.02 d. A general linear mixed model suggested they were detected more during the night than during the day. Common carp preferred habitats near the sandbar and riparian shallow habitats, as revealed by their movement tracks and habitat selection indexes. The general additive mixed model (GAMM) analysis of their shortest distances to riverbanks and depth indicated that they migrated to shallower riparian habitat more frequently during the night than during the day. The continuous wavelet spectrum further confirmed the significant diel pattern of their vertical movement. Their habitat use was also influenced by the water temperature, water level, and river discharge, as suggested by the GAMM. Our results provide novel information on common carp spatiotemporal movement and habitat use patterns, and have important implications for its native population restoration and the invasive population control/exclusion.

Habitat use, movement and activity of two large-bodied native riverine fishes in a regulated lowland weir pool

The construction of dams and weirs, and associated changes to hydrological and hydraulic (e.g., water level and velocity) characteristics of rivers is a key environmental threat for fish. These multiple stressors potentially can affect fish in a variety of ways, including by causing changes in their movement, habitat use and activity. Understanding how and why these changes occur can inform management efforts to ameliorate these threats. In this context, we used acoustic telemetry to examine habitat use, longitudinal movement and activity of two lowland river fishes, Murray cod Maccullochella peelii and golden perch Macquaria ambigua, in a weir pool environment in south-eastern Australia. We compared our results to published studies on riverine populations to determine if their behaviours are similar (or not). We show that M. peelii and M. ambigua in a weir pool exhibited some similar behaviours to conspecific riverine populations, such as strong site fidelity and use of woody habitat for M. ambigua. However, some behaviours, such as large-scale (tens-hundreds of kilometres) movements documented for riverine populations, were rarely observed. These differences potentially reflect flow regulation (e.g., stable water levels, loss of hydraulic cues) in the weir pool. The two species also exhibited contrasting responses to dissolved oxygen conditions in the weir pool, which may reflect differences in their life history. Overall, this study shows that although some aspects of these two native fishes' life history can continue despite flow regulation, other aspects may change in weir pools, potentially impacting on long-term population persistence.

Prolonged exposure to low oxygen improves hypoxia tolerance in a freshwater fish

Persistent hypoxic or low-oxygen conditions in aquatic systems are becoming more frequent worldwide, causing large-scale mortalities to aquatic fauna. It is poorly understood, however, whether species can acclimate to long-term hypoxic conditions. In two experiments, we exposed juvenile freshwater fish (Murray cod, Maccullochella peelii) to low-oxygen conditions and investigated acclimation effects. Experiment 1 determined how responses could be modified by exposure to different temperatures (20, 24 and 28°C) and oxygen conditions (control 6-8 mgO₂ L^-1 and low-oxygen 3-4 mgO₂ L^-1) over 30 days. Experiment 2 determined the acclimation ability of fish exposed to two temperatures (20 and 28°C) and low-oxygen conditions (3-4 mgO₂ L^-1) for three different acclimation periods (7, 14 and 30 days). Responses were measured by determining critical oxygen tension (P _crit), loss of equilibrium and aerobic capacity using resting respirometry. In experiment 1, resting oxygen requirements were negatively affected by long-term low-oxygen exposure except at the highest temperature (28°C). However, long-term acclimation in low-oxygen improved tolerance as measured by loss of equilibrium but not P _crit. In experiment 2, fish could tolerate lower oxygen levels before reaching loss of equilibrium after 7 days acclimation, but this declined overtime. Murray cod were most tolerant to low-oxygen at the lowest temperature (20°C) and shortest exposure time (7 days). Extended low-oxygen exposure resulted in reduced aerobic capacity of fish particularly at the lowest temperature. While prior exposure to low-oxygen may allow fish to cope with hypoxic conditions better in the long-term, acclimation time was inversely related to tolerance, suggesting that resistance to hypoxia might decrease as a function of exposure time. Our study fills a much-needed gap in our understanding of how freshwater species acclimate to hypoxia, and in particular, how exposure to prolonged periods of low-oxygen and elevated temperatures affect organisms physiologically.

Abiotic drivers of activity in a large, free-ranging, freshwater teleost, Murray cod (Maccullochella peelii)

The allocation of time and energy to different behaviours can impact survival and fitness, and ultimately influence population dynamics. Intrinsically, the rate at which animals expend energy is a key component in understanding how they interact with surrounding environments. Activity, derived through locomotion and basic metabolism, represents the principal energy cost for most animals, although it is rarely quantified in the field. We examined some abiotic drivers of variability in locomotor activity of a free-ranging freshwater predatory fish, Murray cod (Maccullochella peelii), for six months using tri-axial accelerometers. Murray cod (n = 20) occupied discrete river reaches and generally exhibited small-scale movements (<5 km). Activity was highest during crepuscular and nocturnal periods when water temperatures were warmest (19-30°C; January-March). As water temperatures cooled (9-21°C; April-June) Murray cod were active throughout the full diel cycle and dormant periods were rarely observed. Light level, water temperature and river discharge all had a significant, non-linear effect on activity. Activity peaked during low light levels, at water temperatures of ~20°C, and at discharge rates of ~400 ML d-1. The temporal changes observed in the behaviour of Murray cod likely reflect the complex interactions between physiological requirements and prey resource behaviour and availability in driving activity, and highlight the importance of empirical field data to inform bioenergetics models.

Using a Population Model to Inform the Management of River Flows and Invasive Carp (Cyprinus carpio)

Carp are a highly successful invasive fish species, now widespread, abundant and considered a pest in south-eastern Australia. To date, most management effort has been directed at reducing abundances of adult fish, with little consideration of population growth through reproduction. Environmental water allocations are now an important option for the rehabilitation of aquatic ecosystems, particularly in the Murray-Darling Basin. As carp respond to flows, there is concern that environmental watering may cause floodplain inundation and provide access to spawning habitats subsequently causing unwanted population increase. This is a management conundrum that needs to be carefully considered within the context of contemporary river flow management (natural, environmental, irrigation). This paper uses a population model to investigate flow-related carp population dynamics for three case studies in the Murray-Darling Basin: (1) river and terminal lakes; (2) wetlands and floodplain lakes; and (3) complex river channel and floodplain system. Results highlight distinctive outcomes depending on site characteristics. In particular, the terminal lakes maintain a significant source carp population regardless of river flow; hence any additional within-channel environmental flows are likely to have little impact on carp populations. In contrast, large-scale removal of carp from the lakes may be beneficial, especially in times of extended low river flows. Case studies 2 and 3 show how wetlands, floodplain lakes and the floodplain itself can now often be inundated for several months over the carp spawning season by high volume flows provided for irrigation or water transfers. Such inundations can be a major driver of carp populations, compared to within channel flows that have relatively little effecton recruitment. The use of a population model that incorporates river flows and different habitats for this flow-responsive species, allows for the comparison of likely population outcomes for differing hydrological scenarios to improve the management of risks relating to carp reproduction and flows.

Testing hypoxia: physiological effects of long-term exposure in two freshwater fishes

Hypoxic or oxygen-free zones are linked to large-scale mortalities of fauna in aquatic environments. Studies investigating the hypoxia tolerance of fish are limited and focused on marine species and short-term exposure. However, there has been minimal effort to understand the implications of long-term exposure on fish and their ability to acclimate. To test the effects of long-term exposure (months) of fish to hypoxia we devised a novel method to control the level of available oxygen. Juvenile golden perch (Macquaria ambigua ambigua), and silver perch (Bidyanus bidyanus), two key native species found within the Murray Darling Basin, Australia, were exposed to different temperatures (20, 24 and 28 °C) combined with normoxic (6-8 mgO₂ L^-1 or 12-14 kPa) and hypoxic (3-4 mgO₂ L^-1 or 7-9 kPa) conditions. After 10 months, fish were placed in individual respirometry chambers to measure standard and maximum metabolic rate (SMR and MMR), absolute aerobic scope (AAS) and hypoxia tolerance. Golden perch had a much higher tolerance to hypoxia exposure than silver perch, as most silver perch died after only 1 month exposure. Golden perch acclimated to hypoxia had reduced MMR at 20 and 28 °C, but there was no change to SMR. Long-term exposure to hypoxia improved the tolerance of golden perch to hypoxia, compared to individuals held under normoxic conditions suggesting that golden perch can acclimate to levels around 3 mgO₂ L^-1 (kPa ~ 7) and lower. The contrasting tolerance of two sympatric fish species to hypoxia highlights our lack of understanding of how hypoxia effects fish after long-term exposure.

Influence of streamflow on spawning-related movements of golden perch Macquaria ambigua in south-eastern Australia

In this study, linkages were examined between movement and spawning behaviour for golden perch Macquaria ambigua in a lowland river by integrating acoustic telemetry and egg and larval drift sampling over 4 years. Movement was strongly seasonal, being most prevalent during the spawning season (spring to early summer), and occurred primarily downstream into the lower river reaches during elevated flows. A very strong association was found between the occurrence of spawning and long-distance M. ambigua movement. The results also revealed that targeted environmental water allocation can promote movement and spawning of this species. By integrating multiple analytical approaches and focusing on key life-history events, this study provides an improved picture of the life history and flow requirements of M. ambigua. The findings can help guide the development of effective environmental flow recommendations.

Who's your mama? Riverine hybridisation of threatened freshwater Trout Cod and Murray Cod

Rates of hybridization and introgression are increasing dramatically worldwide because of translocations, restocking of organisms and habitat modifications; thus, determining whether hybridization is occuring after reintroducing extirpated congeneric species is commensurately important for conservation. Restocking programs are sometimes criticized because of the genetic consequences of hatchery-bred fish breeding with wild populations. These concerns are important to conservation restocking programs, including those from the Australian freshwater fish family, Percichthyidae. Two of the better known Australian Percichthyidae are the Murray Cod, Maccullochella peelii and Trout Cod, Maccullochella macquariensis which were formerly widespread over the Murray Darling Basin. In much of the Murrumbidgee River, Trout Cod and Murray Cod were sympatric until the late 1970s when Trout Cod were extirpated. Here we use genetic single nucleotide polymorphism (SNP) data together with mitochondrial sequences to examine hybridization and introgression between Murray Cod and Trout Cod in the upper Murrumbidgee River and consider implications for restocking programs. We have confirmed restocked riverine Trout Cod reproducing, but only as inter-specific matings, in the wild. We detected hybrid Trout Cod-Murray Cod in the Upper Murrumbidgee, recording the first hybrid larvae in the wild. Although hybrid larvae, juveniles and adults have been recorded in hatcheries and impoundments, and hybrid adults have been recorded in rivers previously, this is the first time fertile F1 have been recorded in a wild riverine population. The F1 backcrosses with Murray cod have also been found to be fertile. All backcrosses noted were with pure Murray Cod. Such introgression has not been recorded previously in these two species, and the imbalance in hybridization direction may have important implications for restocking programs.