Environmental flows aim to mimic components of a river's natural flow variability, including the magnitude, frequency, timing, duration, rate of change and the predictability of flow events. Aspects of the natural flow regime are thought to be linked to critical components of the life history strategies of many riverine fishes, including spawning and recruitment. In the Murray River, Australia, environmental flows are increasingly being used as a restoration tool; however, there is little information about the response of fish to these managed flow events. This study reports on the results from a 3-year study on the effects of water management on the spawning and recruitment of four native fish species in the mid-Murray River system. Two of these years were hydrologically similar, while the third year encompassed an extensive period of floodplain inundation, including the use of the largest environmental flow allocation to date in Australia. Drift nets were used to collect the drifting eggs and larvae of four iconic native species throughout their spawning season each year. Young-of-year were collected in the following autumn. Although golden perch and silver perch eggs were collected in all 3 years, both species increased their spawning activity during the major flood period compared to the previous two seasons. Murray cod and trout cod appeared not to increase their spawning activity in the flood year, but their recruitment may be increased when floodplain inundation occurs at times when their larvae and juveniles are present, most likely through the generation of abundant food resources. Whilst further study is required to confirm the role and mechanism of flooding in the spawning and recruitment of these species; this study provides important evidence of a link between the provision of an environmental flood and fish spawning and recruitment, and has significant implications for managing flows in regulated rivers.
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