Nick S. Whiterod

Freshwater fish conservation in the face of critical water shortages in the southern Murray-Darling Basin, Australia

The lower reaches of the expansive Murray–Darling Basin, Australia, are a hotspot for freshwater biodiversity. The regional ecosystem, however, has been significantly altered by river regulation, including local and catchment-wide water abstraction. Freshwater fishes have suffered from the resultant altered flow regime, together with other threats including habitat degradation and alien species. Impacts reached a critical point (imminent species extinction) during a prolonged drought (1997–2010) that lead to broad-scale habitat loss and drying of refuges during 2007–2010, and urgent conservation measures were subsequently instigated for five threatened small-bodied fish species. A critical response phase included ad hoc interventions that were later incorporated within a broader, coordinated multi-agency program (i.e. the Drought Action Plan and Critical Fish Habitat projects). On-ground actions included local translocation, alien species control, in situ habitat maintenance (e.g. earthworks, environmental water delivery), fish rescues, artificial refuge establishment and captive breeding. Improved river flows signalled an initial phase of recovery in 2011–2012 that included reintroductions. The present paper aims to document the actions undertaken in the Lower Murray, and review successes and lessons from practical examples that will help guide and inform management responses to conserve fish in modified systems subjected to severe water decline.

Flow regulation simplifies a lowland fish assemblage in the Lower River Murray, South Australia

ABSTRACT Regulation has profoundly altered the ecological character of many rivers in the world, with pronounced effects in dryland systems subject to competing demand for water between the environment and society. Pervasive changes to flow regimes have cascading effects on ecological processes and biota attuned to natural variability. The Lower River Murray in south-eastern Australia occupies a curious landscape, being a large lowland river flowing through semi-arid environs fed by a vast inland basin from upstream temperate (River Murray, seasonally predictable) and subtropical-to-desert (Darling River, episodic and highly variable) regions. Extensive regulation via upland dams, water abstraction and serial lowland weirs has reduced mean annual discharge to the sea by two-thirds and transformed riverine hydraulics, leading to dramatic changes in the composition and abundance of biota, including the simplification of a formerly biologically and functionally diverse fish assemblage. Research since the 1980s, often led by the late Keith Forbes Walker, has sought to characterise ecological response to regulation on the Lower River Murray to understand pattern and process and aid in rehabilitation. This paper synthesises a significant body of work relating to freshwater fishes in the river to set a foundation for future monitoring, research and management.

Genetic analyses reveal limited dispersal and recovery potential in the large freshwater crayfish Euastacus armatus from the southern Murray–Darling Basin

Understanding dispersal traits and adaptive potential is critically important when assessing the vulnerability of freshwater species in highly modified ecosystems. The present study investigates the population genetic structure of the Murray crayfish Euastacus armatus in the southern Murray–Darling Basin. This species has suffered significant population declines in sections of the Murray River in recent years, prompting the need for information on natural recruitment processes to help guide conservation. We assessed allele frequencies from 10 polymorphic microsatellite loci across 20 sites encompassing the majority of the species’ range. Low levels of gene flow were observed throughout hydrologically connected waterways, but significant spatial autocorrelation and low migration rate estimates reflect local genetic structuring and dispersal limitations, with home ranges limited to distances <50-km. Significant genetic differentiation of headwater populations upstream of barriers imposed by impoundments were also observed; however, population simulations demonstrate that these patterns likely reflect historical limitations to gene flow rather than contemporary anthropogenic impacts. Dispersal limitations, coupled with its biological traits, suggest that local populations are vulnerable to environmental disturbance with limited potential for natural recolonisation following population decline. We discuss the implications of these findings in the context of managing the recovery of the species.

Calibration of a rapid non-lethal method to measure energetic status of a freshwater fish (Murray cod, Maccullochella peelii peelii)

The energetic status of freshwater fish provides a dynamic measure of their energy balance in response to the environment they occupy. Commercially available microwave technology (the ‘energy meter’) provides a rapid, non-lethal and inexpensive alternative to traditional laboratory methods for the determination of energy density. The energy meter requires species-specific confirmation of the water–lipid relationship, and comparison of energy meter readings with laboratory-determined estimates of the whole-body energy density. I explored the applicability of the energy meter to the threatened Murray cod (Maccullochella peelii peelii), using both hatchery and wild individuals. Although hatchery and wild fish varied in lipid content, water content and energy density, the parameter comparisons necessary to calibrate the energy meter were statistically consistent between both groups. Subsequently, a robust combined water–lipid relationship was identified for Murray cod, where energy density was strongly related to both water content and lipid content. Average energy meter readings were capable of providing a rapid, non-lethal and accurate assessment of Murray cod energy density. The successful calibration highlights the applicability of the energy meter to provide a dynamic measure of the energetic status of threatened freshwater fish throughout the world.

Linking the recruitment and survivorship of a freshwater stream-specialist fish species to flow metrics in Mediterranean climate temporary streams

ABSTRACT Novel modelling was utilised in the present study to reveal significant relationships between the abundance of the Australian freshwater stream-specialist fish Galaxias olidus and metrics defining flow regimes across a region dominated by temporary streams. It was revealed that increases in total abundance were linked to metrics (both 1- and 3-year periods) that indicate greater water availability and the persistence of water in pools across the year, namely the average duration of zero-flow days over the low-flow season (negatively) and total duration of bankfull flows across the year (positively). The analysis identified 3-year metrics as being more important to the abundance of 0+ fish rather than annual ones. Taken together, these findings describing the flow requirements of a stream specialist will help to guide implementation of environmental flows, but will also highlight the need for continued exploration of flow–ecology relationships.