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

Development of an ecosystem approach to the monitoring and management of Western Australian fisheries. Final FRDC report : project 2005/063

Objectives 1. Test the robustness of statistical procedures to identify impacts of multi-sector fishing on community composition using existing fishery data. 2. Assess the level of change in community composition in each bioregion of WA during the previous 30 years. 3. Identify key data to which ecosystem structure and management strategies are most sensitive and which should be collected in the future. 4. Identify critical changes in exploitation and/or environment that would impact marine ecosystems markedly. 5. Identify areas where more detailed research and/or monitoring are needed

Changes in catch rates and length and age at maturity, but not growth, of an estuarine plotosid (Cnidoglanis macrocephalus) after heavy fishing

The hypothesis that heavy fishing pressure has led to changes in the biological characteristics of the estuary cobbler (Cnidoglanis macrocephalus) was tested in a large seasonally open estuary in southwestern Australia, where this species completes its life cycle and is the most valuable commercial fish species. Comparisons were made between seasonal data collected for this plotosid (eeltail catfish) in Wilson Inlet during 2005–08 and those recorded with the same fishery-independent sampling regime during 1987–89. These comparisons show that the proportions of larger and older individuals and the catch rates in the more recent period were far lower, i.e., they constituted reductions of 40% for fish ≥430 mm total length, 62% for fish ≥4 years of age, and 80% for catch rate. In addition, total mortality and fishing-induced mortality estimates increased by factors of ~2 and 2.5, respectively. The indications that the abundance and proportion of older C. macrocephalus declined between the two periods are consistent with the perception of long-term commercial fishermen and their shift toward using a smaller maximum gill net mesh to target this species. The sustained heavy fishing pressure on C. macrocephalus between 1987–89 and 2005–08 was accompanied by a marked reduction in length and age at maturity of this species. The shift in probabilistic maturation reaction norms toward smaller fish in 2005–08 and the lack of a conspicuous change in growth between the two periods indicate that the maturity changes were related to fishery-induced evolution rather than to compensatory responses to reduced fish densities

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

Evaluating the potential use of change-in-ratio and index removal techniques for determining harvest rates and efficiency increases in the Western Rock Lobster Fishery FRDC Project 2009/019

Objectives: 1. Assess current data sources and their potential for estimating harvest rates and increases in efficiency in the western rock lobster fishery using change in ratio and index removal techniques. 2. Evaluate whether additional sources of information are needed to produce more robust estimates of harvest rate and efficiency increase. 3. Assess whether the estimates of harvest rate and fishing efficiency are reliable and could be used for the management of the western rock lobster fishery

Anomalous Hall effect in Rashba two-dimensional electron systems based on narrow-band semiconductors: side-jump and skew scattering mechanisms

We employ a helicity-basis kinetic equation approach to investigate the anomalous Hall effect in two-dimensional narrow-band semiconductors considering both Rashba and extrinsic spin-orbit (SO) couplings, as well as a SO coupling directly induced by an external driving electric field. Taking account of long-range electron-impurity scattering up to the second Born approximation, we find that the various components of the anomalous Hall current fit into two classes: (a) side-jump and (b) skew scattering anomalous Hall currents. The side-jump anomalous Hall current involves contributions not only from the extrinsic SO coupling but also from the SO coupling due to the driving electric field. It also contains a component which arises from the Rashba SO coupling and relates to the off-diagonal elements of the helicity-basis distribution function. The skew scattering anomalous Hall effect arises from the anisotropy of the diagonal elements of the distribution function and it is a result of both the Rashba and extrinsic SO interactions. Further, we perform a numerical calculation to study the anomalous Hall effect in a typical InSb/AlInSb quantum well. The dependencies of the side-jump and skew scattering anomalous Hall conductivities on magnetization and on the Rashba SO coupling constant are examined.Comment: 16 pages, 4 figures, accepted for publication in PR

Quantifying recreational fishing catch and effort: a pilot study of shore-based fishers in the Perth Metropolitan area

Recreational fishing is a popular activity throughout Western Australia, including adjacent to the populous Perth Metropolitan area. Understanding the level of catch and effort associated with this activity is essential for the sustainable management of fish stocks. Whilst the focus of recent surveys in the Perth Metropolitan area has been on boat-based fishers targeting demersal species, shore-based fishing has not been measured for many years. Recent changes to management controls for these demersal species, including the implementation of a fishing boat licence, may increase existing pressures on nearshore stocks by displacing fishing effort onto these resources. Therefore, a need exists for the collection of information on the behaviour and catch of recreational shore-based fishers to support management measures

Statewide survey of boat-based recreational fishing in Western Australia 2015/16

The statewide survey of boat-based recreational fishing includes three components: (i) off-site Phone Surveys (encompassing an initial Screening Survey, a longitudinal Phone-Diary Survey, and Post-Enumeration Surveys); (ii) on-site Boat Ramp Surveys; and (iii) a Remote Camera Survey

An integrated system to survey boat-based recreational fishing in Western Australia 2011/12

The Department of Fisheries developed an integrated system involving several survey methods to provide a more robust approach for obtaining annual estimates of recreational catch by boat based fishers at both state-wide and bioregional levels. These surveys, which used the recently implemented Recreational Fishing from Boat Licence (RFBL) as the basis for sampling, were the most comprehensive ever conducted in Western Australia. They not only provided estimates of catch and effort but provided the information for the validation of these estimates by enabling comparisons across the various methods

Why do people fail to turn good intentions into action? : The role of executive control processes in the translation of healthy eating intentions into action in young Scottish adults

Non peer reviewedPublisher PD