Dry season habitat use of fishes in an Australian tropical river

K Keller,M M Douglas,B J Pusey,S Jackson,M J Kennard,S A Townsend,D A Crook,O J Luiz,Q Allsop,A J King,D Buckle,J Brim Box

doi:10.1038/s41598-019-41287-x

K Keller, M M Douglas + Show 10 more

Open Access

https://doi.org/10.1038/s41598-019-41287-x

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Journal: Scientific Reports	Publication Date: Apr 5, 2019
Citations: 12	License type: open-access

Affiliation: Charles Darwin University, Griffith University

Abstract

The modification of river flow regimes poses a significant threat to the world’s freshwater ecosystems. Northern Australia’s freshwater resources, particularly dry season river flows, are being increasingly modified to support human development, potentially threatening aquatic ecosystems and biodiversity, including fish. More information is urgently needed on the ecology of fishes in this region, including their habitat requirements, to support water policy and management to ensure future sustainable development. This study used electrofishing and habitat survey methods to quantify the dry season habitat use of 20 common freshwater fish taxa in the Daly River in Australia’s wet-dry tropics. Of twenty measured habitat variables, water depth and velocity were the two most important factors discriminating fish habitat use for the majority of taxa. Four distinct fish habitat guilds were identified, largely classified according to depth, velocity and structural complexity. Ontogenetic shifts in habitat use were also observed in three species. This study highlights the need to maintain dry season river flows that support a diversity of riverine mesohabitats for freshwater fishes. In particular, shallow fast-flowing areas provided critical nursery and refuge habitats for some species, but are vulnerable to water level reductions due to water extraction. By highlighting the importance of a diversity of habitats for fishes, this study assists water managers in future decision making on the ecological risks of water extractions from tropical rivers, and especially the need to maintain dry season low flows to protect the habitats of native fish.

Highlights

Freshwater ecosystems are threatened around the world by flow modification[1]
In the wet-dry tropics of Northern Australia, this effect of flow is evident at the end of the dry season when water levels are at their lowest due to reduced rainfall, and factors such as competition and predation can strongly influence fish community structure[21,22]
This study aims to explore the dry season habitat use of freshwater fishes in the Daly River, Northern Territory; a perennial river with a largely unmodified flow regime in Australia’s wet-dry tropics

Summary

Introduction

Freshwater ecosystems are threatened around the world by flow modification[1]. Flow modification can be attributed to a number of human-related activities including urbanisation, industrialisation, mining and agriculture arising from anthropogenic structures such as dams, reservoirs, levee’s and channelization[1,2,3]. In the wet-dry tropics of Northern Australia, this effect of flow is evident at the end of the dry season when water levels are at their lowest due to reduced rainfall, and factors such as competition and predation can strongly influence fish community structure[21,22]. In these systems, aquatic organisms have developed different modes of adaptation (e.g. life history, behaviour, morphology) in response to the seasonal timing and predictability of flow events[4,23]. Several studies indicate that the combination of persistent, predictable flows and habitat complexity are important in promoting and maintaining species specialisation and diversification in tropical rivers[10,24,25]

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