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Mulloway (Argyrosomus japonicus) in Mosman Bay, Western Australia produce three call categories associated with spawning behavior. The determination of call source levels and their contribution to overall recorded sound pressure levels is a significant step towards estimating numbers of calling fish within the detection range of a hydrophone. The source levels and ambient noise also provide significant information on the impacts anthropogenic activity may have on the detection of A. japonicus calls. An array of four hydrophones was deployed to record and locate individual fish from call arrival-time differences. Successive A. japonicus calls produced samples at various ranges between 1 and 100 m from one of the array hydrophones. The three-dimensional localization of calls, together with removal of ambient noise, allowed the determination of source levels for each call category using observed trends in propagation losses and interference. Mean source levels (at 1 m from the hydrophone) of the three call categories were calculated as 163 ± 16 dB re 1 μPa for Category 1 calls (short call of 2–5 pulses); 172 ± 4 dB re 1 μPa for Category 2 calls (long calls of 11–32 pulses); and 157 ± 5 dB re 1 μPa for Category 3 calls (series of successive calls of 1–4 pulses, increasing in call rate).

Spanish mackerel, Scomberomorus commerson, is a species of economic and artisanal importance throughout the Indo-West Pacific region. In this study a total of 2973 S. commerson were examined in a comprehensive study of otolith structure and demographic characteristics across multiple management regions along the Western Australian (WA) coast. Marginal increment analysis of sagittal otoliths showed a single annual peak in opaque zone formation indicating that one opaque and translucent band (annuli) is formed each year. Juvenile S. commerson of undifferentiated sex (n=67; 58-709mm FL) ranged in age from 23 days to 350 days. Males (n=1239; 301-1381mm FL) ranged in age from 80 days to 22yrs, and females (n=1273; 396-1720mm FL) ranged in age from 122 days to 18yrs. Significant differential growth was evident between sexes, with females attaining a larger size-at-age than males. Initial growth of S. commerson is rapid with both sexes reaching maturity within 1.5yrs of age. Growth parameters also differed among regions. The instantaneous rate of natural mortality (M) was estimated to be in the range of 0.16-0.20yr -1. The instantaneous rate of total mortality (Z) estimated from catch at age data for fully recruited age classes, was different between sexes and among regions. Significant differences in demography, age structure and otolith readability among management regions support earlier studies that have documented meta-population structure in S. commerson and underpin the regional management regime for this species in Western Australia. Populations of S. commerson have a high production potential given their rapid initial rate of growth and low age at maturity. Despite this high production potential, productivity of this species in WA is relatively low compared to related fisheries throughout the Indo-Pacific region. © 2012.

Life history characteristics of snapper (Pagrus auratus) were found to vary at fine spatial scales (less than tens of kilometres) in the sub-tropical waters of Shark Bay, Western Australia, from research undertaken between 1997 and 2004. Differences in the timing and duration of the spawning season, length and age at maturity, and maximum age and growth between snapper from the Eastern Gulf, Denham Sound and Freycinet Estuary were attributed to spatial differences in environmental conditions and density-dependent responses to fishing-induced changes in spawning biomass. Such fine-scale spatial variation in the biological characteristics of snapper is consistent with results of previous stock identification studies and further supports the geographic scale at which local snapper stocks are managed to protect both stock productivity and genetic diversity.

The accurate ranging of sounds produced by fish can provide valuable information on species ecology, and fish calls are being increasingly used to delineate and evaluate spawning grounds. In 2008, a single hydrophone was deployed on the riverbed of the Swan River, Western Australia, to assess the most effective technique for ranging mulloway (Argyrosomus japonicus) calls. During this experiment, the ranges of a calling mulloway were calculated using four techniques. These techniques involved comparing the characteristics of the direct and surface -reflected paths using: 1) arrival-time difference; 2) the pressure-amplitude ratios; 3) pulse sound-pressure-level ratios and; 4) a combination of techniques 1) and 2). Technique 1 proved the most consistent ranging technique, with accuracy limited by wave-motion-induced variation in water depth. However, a combination of the tested techniques is recommended when ranging fish.

Aim: This study investigated the use of stable δ13C and δ18O isotopes in the sagittal otolith carbonate of narrow-barred Spanish mackerel, Scomberomorus commerson, as indicators of population structure across Australia. Location: Samples were collected from 25 locations extending from the lower west coast of Western Australia (30°), across northern Australian waters, and to the east coast of Australia (18°) covering a coastline length of approximately 9500 km, including samples from Indonesia. Methods: The stable δ13C and δ18O isotopes in the sagittal otolith carbonate of S. commerson were analysed using standard mass spectrometric techniques. The isotope ratios across northern Australian subregions were subjected to an agglomerative hierarchical cluster analysis to define subregions. Isotope ratios within each of the subregions were compared to assess population structure across Australia. Results: Cluster analysis separated samples into four subregions: central Western Australia, north Western Australia, northern Australia and the Gulf of Carpentaria and eastern Australia. Isotope signatures for fish from a number of sampling sites from across Australia and Indonesia were significantly different, indicating population separation. No significant differences were found in otolith isotope ratios between sampling times (no temporal variation). Main conclusions: Significant differences in the isotopic signatures of S. commerson demonstrate that there is unlikely to be any substantial movement of fish among these spatially discrete adult assemblages. The lack of temporal variation among otolith isotope ratios indicates that S. commerson populations do not undergo longshore spatial shifts in distribution during their life history. The temporal persistence of spatially explicit stable isotopic signatures indicates that, at these spatial scales, the population units sampled comprise functionally distinct management units or separate ‘stocks’ for many of the purposes of fis