Marine and Freshwater Research Marine and Freshwater Research Society
Advances in the aquatic sciences

Effects of freshwater flow on the year-class strength of a non-diadromous estuarine finfish, king threadfin (Polydactylus macrochir), in a dry-tropical estuary

Ian A. Halliday A C , Julie B. Robins A , David G. Mayer B , Jonathan Staunton-Smith A and Michelle J. Sellin A
+ Author Affliations
- Author Affliations

A Department of Primary Industries and Fisheries, Southern Fisheries Centre, 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:

Marine and Freshwater Research 59(2) 157-164
Submitted: 13 April 2007  Accepted: 11 January 2008   Published: 27 February 2008


The year-class strength of the commercial catch of king threadfin (Polydactylus macrochir (Gunther, 1876)) was correlated with freshwater flows into a dry-tropical estuary over five consecutive years. The year-class strength of king threadfin, a non-diadromous estuarine species, fluctuated and correlated significantly with freshwater flow and coastal rainfall in spring and summer; a result similar to that found for the catadromous barramundi (Lates calcarifer) within the same estuarine system. All sub-sets general linear models were used to screen relationships between year-class strength and freshwater variables. King threadfin spawn from spring to summer in north-eastern Australia, when hydrological conditions adjacent to estuaries have high salinities and are optimal for egg and post-larval survival. Young-of-the-year enter estuaries during the wet season, enabling them to take advantage of salinity gradients and the seasonal blooms in prey species such as Acetes spp. and juvenile penaeids that are accentuated in wet years. Freshwater flows in spring and summer are important drivers of the year-class strength of estuarine finfish, and reduction in these flows, through the development of water infrastructure and abstraction or long-term climate change, will potentially reduce the size of the population of estuarine fish available for human harvest.

Extra keywords: environmental flows, fish recruitment, otoliths, year-class strength (YCS).


The present study was funded by the Cooperative Research Centre for Coastal Zone Estuary and Waterway Management and the Fisheries Research and Development Corporation. We thank the seafood processors and commercial fishers of the Fitzroy River region for their cooperation and allowing access to the commercial catch of king threadfin. Technical support was provided by Richard Marsh, Nicola Barnard, Marie Younger and Denise White. We also thank Infofish Services for providing access to the ANSA tag–recapture data and Gary Hargraves, Hans Mulder, Mike Keane (Department of Natural Resources, Mines and Water, Queensland) and Quentin Rider (Fitzroy River Water) for providing freshwater flow data.


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