The western blue groper (Achoerodus gouldii), a protogynous hermaphroditic labrid with exceptional longevity, late maturity, slow growth, and both late maturation and sex change

The western blue groper (Achoerodus gouldii) is shown to be a temperate protogynous hermaphrodite, which spawns between early winter and mid-spring. Because A. gouldii changes body color at about the time of sex change, its color can be used as a proxy for sex for estimating the size and age at sex change and for estimating growth when it is not possible to use gonads for determining the sex of this fish. The following characteristics make A. gouldii highly susceptible to overfishing: 1) exceptional longevity, with a maximum age (70 years) that is by far the greatest yet estimated for a labrid; 2) slow growth for the first 15 years and little subsequent growth by females; and 3) late maturation at a large total length (TL50 = 653 mm) and old age (~17 years) and 4) late sex change at an even greater total length (TL50 = 821 mm) and age (~35 years). The TL50 at maturity and particularly at sex change exceeded the minimum legal total length (500 mm) of A. gouldii and the lengths of many recreationally and commercially caught fish. Many of these characteristics are found in certain deep-water fishes that are likewise considered susceptible to overfishing. Indeed, although fishing effort for A. gouldii in Western Australia is not particularly high, per-recruit analyses indicate that this species is already close to or fully exploited

Biological characteristics and mortality of western butterfish (Pentapodus vitta), an abundant bycatch species of prawn trawling and recreational fishing in a large subtropical embayment

The western butterfish (Pentapodus vitta) is numerous in the bycatch of prawn trawling and recreational fishing in Shark Bay, Western Australia. We have thus determined crucial aspects of its biological characteristics and the potential impact of fishing on its abundance within this large subtropical marine embayment. Although both sexes attained a maximum age of 8 years, males grow more rapidly and to a larger size. Maturity is attained at the end of the first year of life and spawning occurs between October and January. The use of a Bayesian approach to combine independent estimates for total mortality, Z, and natural mortality, M, yielded slightly higher point estimates for Z than M. This result indicates that P. vitta is lightly impacted by fishing. It is relevant that, potentially, the individuals can spawn twice before recruitment into the fishery and that 73% of recreationally caught individuals are returned live to the water

A new proportionality-based back-calculation approach, which employs traditional forms of growth equations, improves estimates of length at age

The performance of a new proportionality-based back calculation approach, describing the relationship between length, otolith size and age using traditional growth curves and assuming a bivariate distribution of deviations from those curves, was evaluated. Cross-validation was used for six teleost species to compare predictions of expected lengths or otolith sizes at age, given otolith size or length, respectively, with those of other proportionality-based approaches that incorporate age. For four species, and particularly Acanthopagrus butcheri when using a biological intercept, better estimates were produced using the new model than were produced using the regression equations in the other back-calculation approaches. Back-calculated lengths for A. butcheri estimated using this model were more consistent with observed lengths, particularly when employing a biological intercept, than those obtained using other proportionality-based approaches and also a constraint-based approach known to produce reliable estimates. By selecting somatic and otolith growth curves from a suite of alternatives to better describe the relationships between length, otolith size, and age, the new approach is likely to produce more reliable estimates of back-calculated length for other species.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Similarities between Line Fishing and Baited Stereo-Video Estimations of Length-Frequency: Novel Application of Kernel Density Estimates

<div><p>Age structure data is essential for single species stock assessments but length-frequency data can provide complementary information. In south-western Australia, the majority of these data for exploited species are derived from line caught fish. However, baited remote underwater stereo-video systems (stereo-BRUVS) surveys have also been found to provide accurate length measurements. Given that line fishing tends to be biased towards larger fish, we predicted that, stereo-BRUVS would yield length-frequency data with a smaller mean length and skewed towards smaller fish than that collected by fisheries-independent line fishing. To assess the biases and selectivity of stereo-BRUVS and line fishing we compared the length-frequencies obtained for three commonly fished species, using a novel application of the Kernel Density Estimate (KDE) method and the established Kolmogorov–Smirnov (KS) test. The shape of the length-frequency distribution obtained for the labrid <i>Choerodon rubescens</i> by stereo-BRUVS and line fishing did not differ significantly, but, as predicted, the mean length estimated from stereo-BRUVS was 17% smaller. Contrary to our predictions, the mean length and shape of the length-frequency distribution for the epinephelid <i>Epinephelides armatus</i> did not differ significantly between line fishing and stereo-BRUVS. For the sparid <i>Pagrus auratus</i>, the length frequency distribution derived from the stereo-BRUVS method was bi-modal, while that from line fishing was uni-modal. However, the location of the first modal length class for <i>P. auratus</i> observed by each sampling method was similar. No differences were found between the results of the KS and KDE tests, however, KDE provided a data-driven method for approximating length-frequency data to a probability function and a useful way of describing and testing any differences between length-frequency samples. This study found the overall size selectivity of line fishing and stereo-BRUVS were unexpectedly similar.</p></div

Results of Kolmogorov–Smirnov (KS) and kernel density estimate (KDE) tests of differences between pairs of fish length-frequency distributions sampled by line fishing and baited remote underwater stereo-video.

<p>Results of Kolmogorov–Smirnov (KS) and kernel density estimate (KDE) tests of differences between pairs of fish length-frequency distributions sampled by line fishing and baited remote underwater stereo-video.</p

Length-frequency distribution for <i>Choerodon rubescens</i>, <i>Epinephelides armatus</i> and <i>Pagrus auratus</i> sampled using either line fishing (Line) or stereo-BRUVS.

<p>The separate bandwidth ‘h’ of each KDE was chosen by the Sheather & Jones (1991) bandwidth selection procedure. Length classes for the histogram of each species were chosen to match the KDE; <i>C. rubescens</i> 50 mm, <i>E. armatus</i> 40 mm and <i>P. auratus</i> 50 mm. Rug plot just above the x-axis indicate individual length observations. Dashed vertical lines indicate the minimum legal length of retention for each species and ‘n’, indicates the sample size.</p

Minimum legal length of retention (MLL), length-frequency mean and standard deviation (SD) and mode, estimated by the kernel density estimate (KDE) for <i>Choerodon rubescens</i>, <i>Epinephelides armatus</i> and <i>Pagrus auratus</i> sampled by fishing (Line) and baited remote underwater stereo-video (stereo-BRUVS).

<p>Minimum legal length of retention (MLL), length-frequency mean and standard deviation (SD) and mode, estimated by the kernel density estimate (KDE) for <i>Choerodon rubescens</i>, <i>Epinephelides armatus</i> and <i>Pagrus auratus</i> sampled by fishing (Line) and baited remote underwater stereo-video (stereo-BRUVS).</p

Map of Western Australia, showing the sampling locations at (A) the Houtman-Abrolhos Islands and Rottnest Island, adjacent to the Perth metropolitan area.

<p>(B) Forward-facing baited remote underwater stereo-video system (stereo-BRUVS).</p