Connectivity, habitat, and flow regime influence fish assemblage structure: Implications for environmental water management in a perennial river of the wet–dry tropics of northern Australia

Bradley J. Pusey, Michael Douglas, Julian D. Olden, Sue Jackson, Quentin Allsop, Mark J. Kennard

Research output: Contribution to journalArticle

Abstract

Environmental water management seeks to balance competing demands between the water needed to sustain human populations and their economic activities and that required to sustain functioning freshwater ecosystems and the species they support. It must be predicated on an understanding of the environmental, hydrological, and biological factors that determine the distribution and abundance of aquatic species. The Daly River of the wet–dry tropics of northern Australia consists of a perennially flowing main stem and large tributaries, as well as many small to large naturally intermittent tributaries, and associated off-channel wetlands. Increased groundwater abstraction to support irrigated agriculture during the dry season threatens to reduce dry-season flows that maintain perenniality and persistence of freshwater fishes. Fish assemblages were surveyed at 55 locations during the dry season over a 2-year period with the goal of establishing the key landscape-scale and local-scale (i.e. habitat) drivers of fish species distribution. Longitudinal (upstream/downstream) and lateral (river/floodplain) gradients in assemblage structure were observed with the latter dependent on the position in the river landscape. Underlying these gradients, stream flow intermittency influenced assemblage composition, species richness, and body size distributions. Natural constraints to dispersal were identified and their influence on assemblage structure was also dependent on position within the catchment. Eight distinct assemblage types were identified, defined by differences in the abundance of species within five groups differing in functional traits describing body size, spawning requirements, and dispersal capacity. These functional groups largely comprised species widely distributed in northern Australia. The results of the study are discussed with reference to the environmental flow needs of the Daly River and other rivers of northern Australia. The findings may also be applied to environmental flow management in savannah rivers elsewhere.

Original languageEnglish
Pages (from-to)1-15
Number of pages15
JournalAquatic Conservation: Marine and Freshwater Ecosystems
Volume30
Issue number7
Early online date8 Jun 2020
DOIs
Publication statusPublished - Jul 2020

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