title: Shock, stress or signal? Implications of freshwater flows for a top-level estuarine predator.
abstract: Physicochemical variability in estuarine systems plays an important role in estuarine processes and in the lifecycles of estuarine organisms. In particular, seasonality of freshwater inflow to estuaries may be important in various aspects of fish lifecycles. This study aimed to further understand these relationships by studying the movements of a top-level estuarine predator in response to physicochemical variability in a large, temperate south-east Australian estuary (Shoalhaven River). Mulloway (Argyrosomus japonicus, 47-89 cm total length) were surgically implanted with acoustic transmitters, and their movements and migrations monitored over two years via fixed-position VR2W acoustic receivers configured in a linear array along the length of the estuary. The study period included a high degree of abiotic variability, with multiple pulses (exponentially high flows over a short period of time) in fresh water to the estuary, as well as broader seasonal variation in flow, temperature and conductivity. The relative deviation of fish from their modal location in the estuary was affected primarily by changes in conductivity, and smaller fish (n = 4) tended to deviate much further downstream from their modal position in the estuary than larger fish (n = 8). High-flow events which coincided with warmer temperatures tended to drive mature fish down the estuary and potentially provided a spawning signal to stimulate aggregation of adults near the estuary mouth; however, this relationship requires further investigation. These findings indicate that pulse and press effects of freshwater inflow and associated physicochemical variability play a role in the movements of mulloway, and that seasonality of large freshwater flows may be important in spawning. The possible implications of river regulation and the extraction of freshwater for consumptive uses on estuarine fishes are discussed.
authors.affiliation: Port Stephens Fisheries Institute, NSW Department of Primary Industries, Nelson Bay, New South Wales, Australia; School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Taylor
authors.affiliation: School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia; Batemans Bay Fisheries Centre, NSW Department of Primary Industries, New South Wales, Australia.
authors.forename: Dylan E
authors.initials: DE
authors.lastname: van der Meulen
authors.affiliation: Environmental Change Institute, Oxford University Centre for the Environment, University of Oxford, United Kingdom.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Ives
authors.affiliation: Batemans Bay Fisheries Centre, NSW Department of Primary Industries, New South Wales, Australia.
authors.forename: Chris T
authors.initials: CT
authors.lastname: Walsh
authors.affiliation: NSW Office of Water, Wollongong, New South Wales, Australia.
authors.forename: Ivars V
authors.initials: IV
authors.lastname: Reinfelds
authors.affiliation: School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales, Australia; WildFish Research, Sydney, New South Wales, Australia.
authors.forename: Charles A
authors.initials: CA
authors.lastname: Gray
mesh_terms: D000818:Animals; D063366:Estuaries; D005399:Fishes / Q000502:physiology; D005618:Fresh Water; D012621:Seasons
references.citation: J Fish Biol. 2010 Jun;76(9):2067-89
references.pmid: 20557655
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references.pmid: 21470729
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references.pmid: 22039470