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.

Spawning, maturity, growth and movement of Platycephalus fuscus (Cuvier, 1829) (Platycephalidae): fishery management considerations

“…flood event) or what biotic/abiotic factors triggered such movements. Acoustic telemetry studies are required to better determine the rates of exchanges of dusky flathead between estuaries and coastal waters and relationships with key ecological processes (Walsh et al., ; Payne et al., ; Taylor et al., ). Nevertheless, as most of these distant recaptures occurred during the summer spawning period, we suggest that the predominant northerly directed movement displayed by these expatriated P. fuscus is potentially a life‐history tactic associated with reproduction to facilitate the dispersal of eggs and larvae to nursery areas by the southward‐flowing East Australian Current, as proposed for other species (Gray et al., ).…”

Rapid salinity changes affect the survival and physiology of a penaeid prawn: Implications of flood events on recruitment to the fishery

“…Stochastic environmental events, such as extreme changes in temperature or high rainfall, can cause dramatic physiochemical changes in estuaries that may affect aquatic organisms (e.g. Boesch, Diaz & Virnstein, ; Owen & Forbes, ; Payne et al., ; Preen, Lee Long & Coles, ; Taylor et al., ). Large rainfall events can dramatically reduce water salinity within 24 hr (Blöschl & Sivapalan, ; Robinson & Sivapalan, ) and salinity may remain low for weeks afterwards (Taylor et al., ).…”

“…Boesch, Diaz & Virnstein, ; Owen & Forbes, ; Payne et al., ; Preen, Lee Long & Coles, ; Taylor et al., ). Large rainfall events can dramatically reduce water salinity within 24 hr (Blöschl & Sivapalan, ; Robinson & Sivapalan, ) and salinity may remain low for weeks afterwards (Taylor et al., ). The frequency and intensity of large rainfall events are predicted to increase in the future (Pachauri et al., ); therefore, the potential impacts of these events on aquatic species will need to be considered by natural resource managers (e.g.…”

Development and ossification of the feeding apparatus in the larvae of two co‐occurring species of kob (Sciaenidae), Argyrosomus japonicus and Argyrosomus inodorus, in South Africa

“…Members of A. japonicus are highly mobile and undertake coastal migrations (Sasaki, 1989;Griffiths, 1996;Taylor et al, 2014). Populations of both A. japonicus and A. inodorus off the coast of South Africa have been heavily exploited and the current stock of A. japonicus is considered collapsed (Cowley et al, 2008;Palmer & Snowball, 2009), with A. inodorus entering a recovery phase after drastic efforts to reduce quotas in the commercial line fishery (Winker et al, 2013).…”