From an irrigation system to an ecological asset: adding environmental flows establishes recovery of a threatened fish species

Abstract

Worldwide, riverine fish are the target of environmental water because populations have declined in lotic river habitats following river regulation. Murray cod is an endangered Australian riverine fish with remaining populations associated with lotic river reaches with instream habitat, including some creeks operated as part of irrigation systems. Our objectives were to develop a life history model, apply the building block method of environmental flows to enhance the abundance of juvenile Murray cod and promote population recovery. From 2008 to 2018 we evaluated changes to Murray cod juvenile abundance before and after implementation of a perennial environmental flow regime that began in 2013. During the first year of the environmental flow, larvae were collected as evidence of spawning. Murray cod abundance can be enhanced with environmental flows that target: (1) an annual spring spawning or recruitment flow with no rapid water level drops; (2) maximising hydrodynamic complexity (i.e. flowing habitats that are longitudinally continuous and hydrodynamically complex); and (3) an annual base winter connection flow. Recognition that incorporating hydraulics (water level and velocity) at fine and coarse time scales, over spatial scales that reflect life histories, provides broader opportunities to expand the scope of environmental flows to help restore imperilled fish species in regulated ecosystems.

Riverine spawning, long distance larval drift, and floodplain recruitment of a pelagophilic fish: A case study of golden perch (Macquaria ambigua) in the arid Darling River, Australia

“…A similar approach may also be applicable in the northern MDB, where the Macintyre–Barwon and Weir rivers are confirmed spawning locations for golden perch (Reynolds, ; Rolls et al, ) and where other tributaries (Paroo, Culgoa, Warrego, Moonie, Condamine–Balonne rivers) are also likely to serve as spawning and recruitment habitats (Balcombe et al, ; Rolls et al, ). By systematically identifying important tributary habitats, local actions can be applied (Hermoso, Abell, Linke, & Boon, ; Embke et al, ; Stuart, Sharpe, Stanislawski, Parker, & Mallen‐Cooper, ), such as protecting refuge water holes and the first spring/summer flows that serve as migration or spawning cues, when there is a sharp rise from low‐flow antecedent conditions. Such actions can help maintain the natural functioning of these rivers, most notably for the downstream export of fish larvae into receiving riverine or floodplain nursery habitats.…”

Underlying trends confound estimates of fish population responses to river discharge

“…The discharge metrics each reflected one of four time periods based on the life history of our study species and the effects of river regulation on discharge regimes in our study systems. These metrics build on previous studies of associations between discharge and recruitment for our study species (Humphries et al., 1999, 2020; King et al., 2009; Koster et al., 2017; Stuart et al., 2019; Tonkin et al., 2019, 2020). The discharge metrics were: (1) maximum 3‐day proportional change in discharge in the 12 months prior to sampling; (2) median daily discharge in September–November prior to sampling; (3) median daily discharge in December–March prior to sampling; (4) median daily discharge in May–July prior to sampling; (5) maximum daily discharge in the 12–24 months prior to sampling; and (6) the number of days in the 12 months prior to sampling with discharge below its long‐term (1991–present) 10th percentile.…”

Contrasting natal origin and movement history informs recovery pathways for three lowland river species following a mass fish kill

“…Murray cod spawn annually, although the presence of gaps in numerous age classes suggests that recruitment in the lower Darling River is variable. To rebuild populations, recruitment needs to be supported by the provision of hydraulically complex, flowing water habitats at key times to support growth and survival (Tonkin et al 2017(Tonkin et al , 2021Mallen-Cooper and Zampatti 2018;Stuart et al 2019). Indeed, Murray cod are often a focal species for environmental water allocation within the MDB, and the storage and subsequent reregulation of water in the Menindee Lakes means that targeted environmental flows can be delivered to the lower Darling River to support population restoration (Koehn et al 2014;Sharpe and Stuart 2018).…”