Flows for native fish in the Murray‐Darling Basin: lessons and considerations for future management

Abstract

Summary Increased regulation and extraction of water from rivers has contributed to the decline of fishes, and the use of environmental water allocations (EWAs) is now a key rehabilitation measure. Major reform of water policy in the Murray‐Darling Basin (MDB), Australia, has recently provided significant EWAs to improve ecological outcomes. Conflict over water buybacks, the value of the water and the need to maximise environmental benefits and minimise risks of unwanted outcomes has increased the expectation for science to underpin and justify such actions. Recent research has focussed attention on the need to understand fish–flow relationships. The Native Fish Strategy for the Murray‐Darling Basin 2003–2013 (NFS), while not specifically targeted at water policy reform or water delivery, has provided fish ecology research and flow restoration experimentation and contributed considerable new scientific knowledge to support flow management. It has contributed to a substantial and positive change in environmental watering for fish, with native fish targets now regularly incorporated into watering objectives. This study documents changes to water management in the MDB, summarises current knowledge of flow‐related fish ecology in the MDB, highlights the benefits and risks of some water management practises and provides recommendations for future management and research. A major recommendation is the need for a coordinated, cross‐jurisdictional approach to flow restoration for native fish, ensuring that the best available science is being used in all watering allocations. We caution on the use of environmental works such as regulators to artificially inundate floodplains and suggest that such approaches should be viewed as large‐scale experiments with the significant risks posed to fish needing to be recognised, adequately monitored and adaptively managed.

Identifying environmental correlates of intraspecific genetic variation

“…Thus, our findings suggest that river reaches across the MDB that have more disturbed flow regimes are likely to support larger, more genetically diverse populations of Murray cod. Although this result seems counterintuitive because many native fish species are adversely affected by river regulation (Koehn et al, 2014), more consistent, perennial flows observed in regulated channels may reduce the frequency of population bottlenecks that can occur during the dry phases that typify the highly variable and unpredictable natural flow regime in the MDB . In the MDB the greatest disturbance to the natural flow regime typically occurs in lowland river reaches where river regulation and water extraction for irrigation support agricultural production.…”

“…Flow-related variables are commonly identified as important predictors of species occurrence patterns in rivers, with flow considered a 'master variable' strongly associated with habitat complexity, geomorphology and many key physicochemical properties of rivers including temperature, pH and oxygen concentration (Poff et al, 1997). Disruption to a river's natural flow regime as a result of human activities (for example, flow regulation, construction of dams and weirs and water extraction) can have negative consequences for biodiversity, but may benefit some species Koehn et al, 2014). For example, in environments with highly variable and unpredictable natural flow regimes, flow-dependent species may benefit from artificially induced perennial flows .…”

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

“…Given that the long potential spawning season for carp can overlap with the environmental watering needs of many native fishes and other biota (vegetation, waterbirds; MDBA 2011) careful management of the associated risks relating to carp spawning and recruitment is needed. Managing environmental water is a relatively new science, particularly within an adaptive management framework; consequently, both scientists and managers need to continue to formally learn and garner knowledge from watering actions (Koehn et al 2014). The use of tools such as the population model demonstrated in this study, can assist this process by allowing scenario analysis and the exploration of the relative likely outcomes of alternative management actions so that can help tradeoffs can be evaluated.…”

“…High levels of water abstraction have placed significant pressure on aquatic ecosystems in the MDB, and many rivers are considered in poor health (Davies et al 2010). In response, environmental water allocations are now considered essential for the rehabilitation of its aquatic ecosystems (MDBA 2011;Koehn et al 2014) and initiatives such as the basin plan (MDBA 2011), are increasing the availability of environmental water (water delivered for environmental, not consumptive objectives; see Arthington 2012) in an attempt to rehabilitate riverine ecosystems, including native fishes (MDBA 2011;Koehn and Lintermans 2012).…”

“…The delivery of environmental water is not intended to benefit carp, but as carp can readily move and spawn in response to flows, there is concern that their populations may benefit from some allocations (Conallin et al 2012Koehn et al 2014). Given the poor public perception of carp in Australia, this would be an undesirable outcome for environmental watering, and indeed may negate some of the intended benefits for native species.…”