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.