Does the quantity and timing of fresh water flowing into a dry tropical estuary affect year-class strength of barramundi (Lates calcarifer)?
Jonathan Staunton-Smith A C , Julie B. Robins A , David G. Mayer A B , Michelle J. Sellin A and Ian A. Halliday AA Department of Primary Industries and Fisheries, Southern Fisheries Centre, PO Box 76, Deception Bay, Qld 4508, Australia.
B Department of Primary Industries and Fisheries, Animal Research Institute, Locked Mail Bag 4, Moorooka, Qld 4105, Australia.
C Corresponding author. Email: jonathan.staunton-smith@dpi.qld.gov.au
Marine and Freshwater Research 55(8) 787-797 https://doi.org/10.1071/MF03198
Submitted: 15 December 2003 Accepted: 27 October 2004 Published: 16 November 2004
Abstract
The influence of fresh water flowing into estuaries on biological processes, such as recruitment of juvenile fish, is poorly understood, but important if freshwater resources are to be managed sustainably. Typically, lagged correlations between freshwater flows and fisheries production (i.e. catch) are used to support speculation that flows affect the survival of fish (and thus year-class strength) during their first year of life. The present study compares the relative strength of year classes in an estuarine fish population with two indices of fresh water flowing into the estuary, river flow and coastal rainfall. Year-class strength was estimated from a subset of the age structure of commercially caught adult barramundi (Lates calcarifer), which were sampled at seafood processors for three consecutive years. Strong and coherent fluctuations in year-class strength were observed. Positive correlations were found between the abundance of year classes (accounting for age) and quantity of fresh water flowing into the estuary during spring and summer, when barramundi spawn and young-of-the-year recruit to nursery habitats. Regression analysis was used to explore the relationships between year-class strength and environmental variables. A possible, but unproven, causal mechanism for the relationship is that the quantity of fresh water flowing into the estuary during spring and summer influences the survival of early life-history stages of barramundi (i.e. juvenile recruitment) by altering accessibility, productivity and or carrying capacity of nursery habitats.
Extra keywords: environmental flows, fish recruitment, otoliths, regression analysis, year-class strength.
Acknowledgments
The study was funded by the Cooperative Research Centre for Coastal Zone Estuary and Waterway Management and the Fisheries Research and Development Corporation. We thank Michael Hutchison, Peter Long, David Milton, Gary Fry and Wayne Sumpton and three anonymous reviewers for constructive comments on the manuscript. Nicola Barnard, Denise White and Marie Yonger helped in the laboratory and Bob Packett helped at the seafood processors. We thank Andrew McDougall, John Russell, John Platten, Ken Cowden and Andrew Hamilton for providing us with access to otoliths and data for known-age barramundi. We thank Bill Sawynok and John Platten for the many stimulating discussions about barramundi habits in central Queensland. We thank Peter Long (Department of Primary Industries and Fisheries) for collating fish-stocking data, and Gary Hargraves, Hans Mulder and Mike Keane (Department of Natural Resources, Mines and Energy) and Quentin Rider (Fitzroy River Water) for providing river-flow data. Finally, we thank the seafood processors of Rockhampton and Gladstone and commercial fishers of the Fitzroy River region for cooperation and allowing access to the commercial catch of barramundi.
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