How individuals respond to environmental change determines the strength and direction of biological processes like recruitment and growth that underpin population productivity. Ascertaining the relative importance of environmental factors can, however, be difficult given the numerous mechanisms through which they affect individuals. This is especially true in dynamic and complex estuarine environments. Here, we develop long-term otolith-based indices of recruitment and growth for estuary perch Percalates colonorum (Bemm River, Australia), to explore the importance of intrinsic (individual, demographic) and extrinsic (hydrologic, climatic, density-dependent) factors in driving estuarine fish productivity. Analyses involved a novel zero-inflated specification of catch curve regression and mixed effects modelling. The 39 years of recruitment and 46 years of growth data, spanning a period of environmental change including severe drought, displayed considerable inter-annual variation. Recruitment success was strongly related to high freshwater inflows during the spawning season, suggesting that these conditions act as spawning cues for adults and potentially provide favourable conditions for larvae. Individuals displayed age-dependent growth, with highest rates observed at younger ages in years characterized by warm temperatures, and to a lesser degree, greater magnitude base inflow conditions. We detected systematic among-year-class growth differences, but these were not attributable to year class strength, suggesting that environmental conditions experienced by individuals as juveniles can have long-lasting effects of greater importance to population productivity than density-dependent growth responses. The primacy of temperature in driving growth variation highlights that under-appreciated climatic variation can affect estuarine fish productivity through direct physiological and indirect food web mechanisms. We predict that climatic warming will promote individual growth in southerly populations of P. colonorum but concurrently limit recruitment due to forecast reductions in spawning season river discharge. Disparate trait responses are likely in other fishes as they respond to multiple and changing environmental drivers, making predictions of future population productivity challenging.

Acoustic technology is a common means to study the movements and habitat utilization of aquatic organisms. This study simultaneously assesses the relative importance of a number of major environmental variables affecting the detection range and detection frequency of acoustic tracking technology in near-shore marine environments. Transmitter power output and diel index in order of relative importance were the most influential variables affecting detection range within a temperate reef habitat. Wave height, transmitter power output, and diel index in order of relative importance were the most influential variables affecting detection range within the wash zone. Similar models resulted when examining detection frequency at 100 m within the two habitat types. Attention is also drawn to the selection of transmitter power output based upon the habitat type and environmental conditions of the study site. This study demonstrates the importance of in situ range test studies in array design and interpretation of acoustic telemetry data.

Two methods of otolith increment analysis were used to describe spatial, temporal and gender variation in growth of sand whiting, Sillago ciliata (Cuvier), in four south-east Australian estuaries. Mean annual standardised otolith increment widths were used as indices of individual lifetime growth rates, while raw otolith increment widths were used to describe variation in growth throughout the life of S. ciliata. Temporal variation in growth was observed at an annual scale, while spatial variation in growth was observed between estuaries. Growth rates increased significantly with decreasing latitude and greater mean sea surface temperatures. A divergence in growth rates between sexes was detected, with females growing faster than males after sexual maturity. This study highlights how otolith increment analyses can: (1) be used to analyse temporal trends in growth from a single sample and (2) provide insight into juvenile growth when samples have an absence of undersized fish. K E Y W O R D S :Estuarine, growth rate, otolith annuli, sex, Sillaginidae, temperature.

Aquatic macrophytes are often monitored to detect change in ecosystem function and state, as well as assessing the effectiveness of invasive aquatic plant management. This study compares seven methodologies to monitor the distribution and abundances of aquatic macrophytes. Four line transect methodologies and three spatial mapping techniques were employed in parallel over a broad turbidity gradient in two lentic habitats of south-eastern Australia. The methodologies examined included hydroacoustic surveys, on-site digitising, and digitisation of airborne remote sensing imagery. Variation in estimates of macrophyte coverage were observed between methodologies. Consistency in the collection and interpretation of data was greatest for the line transect methodologies and the digitisation of satellite imagery. Duel-frequency identification sonar proved to be an effective novel hydroacoustic technique to monitor macrophyte abundances over broad spatial scales. Single beam sonar transects was also an objective, repeatable and scalable methodology. Videography and on-site handheld PDA mapping were of limited utility due to restrictions imposed by turbidity. The utility of sidescan sonar could be improved when used in conjunction with on-site handheld PDA mapping. This study outlines important considerations when selecting a methodology to monitor macrophyte distribution and abundance. Results indicate that no one specific method can be employed across all macrophyte monitoring studies. The method or combination of methods employed during macrophyte monitoring studies is dependent upon the study objectives, budget and environmental conditions of the study site.

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