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Type: Journal article
Title: Impacts of drought, flow regime, and fishing on the fish assemblage in southern Australia's largest temperate estuary
Author: Ferguson, G.
Ward, T.
Ye, Q.
Geddes, M.
Gillanders, B.
Citation: Estuaries and Coasts, 2013; 36(4):737-753
Publisher: Springer New York LLC
Issue Date: 2013
ISSN: 1559-2723
1559-2731
Statement of
Responsibility: 
Greg J. Ferguson, Tim M. Ward, Qifeng Ye, Michael C. Geddes, Bronwyn M. Gillanders
Abstract: We analysed a 25-year time series of fishery catch and effort data, and age/size information for four large-bodied, native fish species to investigate the hypotheses that under conditions of reduced freshwater inflows and high fishing pressure: (1) the structure of fish assemblages in the lower Murray River system have changed, (2) species diversity of fishes has declined and (3) population age structures of large-bodied, late-maturing, native fish (Macquaria ambigua, Argyrosomus japonicus, Rhombosolea tapirina and Acanthopagrus butcheri) have been reduced. Annual catches and effort in the lower Murray River system were stable for 25 years, but proportional contribution to the total catch from each of freshwater, estuarine and adjacent marine habitats, and the species within them varied. Fish assemblages generally differed between subsequent 5-year periods, with the exception of 1989–1993 when floods occurred in 4 out of 5 years, and the following 5-year period (1994–1998). Species richness declined steeply over 25 years in freshwater and estuarine habitat and species diversity (Hill’s H 2) also declined after 2001 in estuarine habitat. Species with rapid growth and early maturation (opportunistic strategists), increasingly dominated catches, whilst species with slow growth and late maturation (periodic strategists) declined. Truncated population age structures suggested longevity overfishing of three periodic strategist species: golden perch (M. ambigua), black bream (A. butcheri), mulloway (A. japonicus) and a fourth species with an intermediate strategy, greenback flounder (R. tapirina). This has implications for management because loss of older/larger individuals suggests reduced capacity to withstand or recover from deteriorated environmental conditions associated with a historically extreme drought in the lower Murray River system. Management of these species should seek to preserve the remnant population age structures and then to rebuild age structures by allowing recruits to become established in the adult population. We recommend that assessment of multi-species fisheries in changeable environments, such as occur in estuaries and other end-river environments, requires a suite of indicators that address changes in fish assemblages and populations.
Keywords: Estuaries; species diversity; fish; life history; fishery biology; population characteristics; Australia
Rights: © Coastal and Estuarine Research Federation 2013
RMID: 0020124863
DOI: 10.1007/s12237-012-9582-z
Appears in Collections:Earth and Environmental Sciences publications

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