Small environmental flows, drought and the role of refugia for freshwater fish in the Macquarie Marshes, arid Australia

Abstract

Fish in arid-zone rivers are dependent on waterholes for refuge during drought. In heavily regulated systems, water extraction for human use has the potential to exacerbate drought conditions and increase the reliance of fish on refugia. This study investigated this hypothesis by surveying fish communities at 25 sites in the Ramsar listed Macquarie Marshes, before and after a 23-GL environmental flow event. Although such flows are central to restoration efforts in the Murray-Darling Basin, limited water availability often forces water managers to make difficult triage decisions regarding which ecological assets to service. This study aimed to provide an update on the current health and status of native fish populations in the Macquarie Marshes and discuss how small flows may best be delivered to meet their ecological needs, particularly during droughts. Eight native species were collected, but they were outnumbered by three alien species by more than 3 : 1. Post-flooding recruitment was observed in most species and mean species richness of sampling sites increased significantly, as fish moved out of drought refugia to utilize a more diverse array of microhabitats. This study presents a conceptual model of fish use of refugia and recommends that key low-flow refugia be targeted for remediation efforts.

Does flooding affect spatiotemporal variation of fish assemblages in temperate floodplain wetlands?

“…An associated component of this study compared physicochemical fluctuations in the wetlands studied relative to paired river sites and found that water chemistry was more spatially and temporally variable within wetlands (Beesley et al, 2011). Substantial autumnal recruitment of gambusia has been found in nearby floodplain systems, but has been attributed to environmental watering (23 GL) rather than season (Rayner, Jenkins & Kingsford, 2009). High food density, if coupled with low competition and predation, should increase the survival of larval fish, particularly for species with small and undeveloped larvae, such as carp gudgeon.…”

Mapping inundation in the heterogeneous floodplain wetlands of the Macquarie Marshes, using Landsat Thematic Mapper

“…1b). River regulation has altered river flows to the Marshes (Ren and Kingsford, 2011) and reduced flooding patterns (Thomas et al, 2011;Wen et al, 2013) with detrimental ecological impacts (Kingsford and Thomas, 1995;Kingsford and Johnson, 1998;Rayner et al, 2009;Thomas et al, 2010). The Marshes have access to a volume of environmental water each year (>300 GL) to mitigate the effects of river regulation, targeting the core wetland area.…”

Cost–benefit and water resources policy: a survey

“…The economic value of water comes fiom the many uses to which water can be put to satisfy human needs (Young, 2005) or uses to sustain key ecological assets (Rayner et al, 2009). Water has value in the dimensions of quantity, quality, timing and location.…”