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RESEARCH ARTICLE
Contents Vol 61(11)

Temporal variability in fish assemblage structure and recruitment in a freshwater-deprived estuary: The Coorong, Australia

Brenton P. Zampatti A B , Christopher M. Bice A and Paul R. Jennings A
+ Author Affiliations
- Author Affiliations

A Inland Waters and Catchment Ecology Program, SARDI Aquatic Sciences, PO Box 120, Henley Beach, SA 5022, Australia.

B Corresponding author. Email: brenton.zampatti@sa.gov.au

Marine and Freshwater Research 61(11) 1298-1312 https://doi.org/10.1071/MF10024
Submitted: 2 February 2010  Accepted: 2 June 2010   Published: 16 November 2010

Abstract

River regulation can diminish freshwater flows to estuaries and compromise estuarine functionality. Understanding biotic responses to altered flow regimes is imperative to effectively manage aquatic ecosystems. The present study investigated temporal variation in fish assemblage structure and the recruitment of catadromous fish in the Coorong estuary at the terminus of the Murray River, in south-eastern Australia. Over the three-year study period, freshwater inflows to the estuary diminished and ultimately ceased, disconnecting freshwater and estuarine environments. It was hypothesised that these conditions would lead to (1) increases in estuarine salinities and concomitant changes in fish assemblage structure and abundance, and (2) decreased recruitment of catadromous fish. As freshwater inflow decreased, salinities immediately downstream of a series of tidal barrages increased from brackish to marine–hypersaline, species richness and diversity decreased, freshwater and diadromous species became less abundant and assemblages were increasingly characterised by marine species. Furthermore, the abundance of young-of-year catadromous fish decreased dramatically. Excessive regulation of freshwater inflows is resulting in the Coorong estuary resembling a marine embayment, leading to a loss in species diversity. We suggest, however, that even small volumes of freshwater may promote diversity in estuarine fish assemblages and some recruitment of catadromous species.

Additional keywords: diadromous, drought, Galaxias, Murray River, Pseudaphritis.


Acknowledgements

We thank the following Department of Water, Land and Biodiversity Conservation staff for supporting the establishment and funding of this project: Mandy Rosetto, Ian Burns, Brenton Erdmann, Rohan Henry and Richard Brown. Thanks also to Adrienne Frears and Glynn Ricketts from the South Australian Murray–Darling Basin Natural Resource Management Board for ongoing management and support of the project. To Peter Lewis (deceased), Anthony Jones, Anthony Hobbs, Ray Maynard, Arron Strawbridge and Josh Fredberg and all the other SA Water and SARDI staff who braved four seasons in one day to set and retrieve traps, and assist in processing fish, thanks for all your efforts. Thanks to Luciana Bucater (SARDI) for assistance with figures. We would also like to thank Bronwyn Gillanders, Alan Whitfield, Andrew Boulton and two anonymous reviewers for helpful comments on drafts of this manuscript. This project was funded by the Murray–Darling Basin Commission. All sampling was conducted under an exemption (no. 9902132) of Section 115 of the Fisheries Management Act 2007.


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