Fish assemblages associated with natural and anthropogenically-modified habitats in a marine embayment: Comparison of baited videos and opera-house traps

Marine embayments and estuaries play an important role in the ecology and life history of many fish species. Cockburn Sound is one of a relative paucity of marine embayments on the west coast of Australia. Its sheltered waters and close proximity to a capital city have resulted in anthropogenic intrusion and extensive seascape modification. This study aimed to compare the sampling efficiencies of baited videos and fish traps in determining the relative abundance and diversity of temperate demersal fish species associated with naturally occurring (seagrass, limestone outcrops and soft sediment) and modified (rockwall and dredge channel) habitats in Cockburn Sound. Baited videos sampled a greater range of species in higher total and mean abundances than fish traps. This larger amount of data collected by baited videos allowed for greater discrimination of fish assemblages between habitats. The markedly higher diversity and abundances of fish associated with seagrass and limestone outcrops, and the fact that these habitats are very limited within Cockburn Sound, suggests they play an important role in the fish ecology of this embayment. Fish assemblages associated with modified habitats comprised a subset of species in lower abundances when compared to natural habitats with similar physical characteristics. This suggests modified habitats may not have provided the necessary resource requirements (e.g. shelter and/or diet) for some species, resulting in alterations to the natural trophic structure and interspecific interactions. Baited videos provided a more efficient and non-extractive method for comparing fish assemblages and habitat associations of smaller bodied species and juveniles in a turbid environment

Bottom trawl fishing footprints on the world’s continental shelves

Bottom trawlers land around 19 million tons of fish and invertebrates annually, almost one-quarter of wild marine landings. The extent of bottom trawling footprint (seabed area trawled at least once in a specified region and time period) is often contested but poorly described. We quantify footprints using high-resolution satellite vessel monitoring system (VMS) and logbook data on 24 continental shelves and slopes to 1,000-m depth over at least 2 years. Trawling footprint varied markedly among regions: from 50% in some European seas. Overall, 14% of the 7.8 million-km2 study area was trawled, and 86% was not trawled. Trawling activity was aggregated; the most intensively trawled areas accounting for 90% of activity comprised 77% of footprint on average. Regional swept area ratio (SAR; ratio of total swept area trawled annually to total area of region, a metric of trawling intensity) and footprint area were related, providing an approach to estimate regional trawling footprints when high-resolution spatial data are unavailable. If SAR was ≤0.1, as in 8 of 24 regions, there was >95% probability that >90% of seabed was not trawled. If SAR was 7.9, equal to the highest SAR recorded, there was >95% probability that >70% of seabed was trawled. Footprints were smaller and SAR was ≤0.25 in regions where fishing rates consistently met international sustainability benchmarks for fish stocks, implying collateral environmental benefits from sustainable fishing

Measurements of the t(t)Overbar charge asymmetry using the dilepton decay channel in pp collisions at root s=7 TeV

The tt¯ charge asymmetry in proton-proton collisions at s√ = 7 TeV is measured using the dilepton decay channel (ee, e μ , or μμ ). The data correspond to a total integrated luminosity of 5.0 fb −1 , collected by the CMS experiment at the LHC. The tt and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be A C = −0 . 010 ± 0 . 017 (stat . ) ± 0 . 008 (syst . ) and AlepC = 0 . 009 ± 0 . 010 (stat . ) ± 0 . 006 (syst . ). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the tt¯ system. All measurements are consistent with the expectations of the standard model

Ichthyoplankton assemblages associated with pink snapper (Pagrus auratus) spawning aggregations in coastal embayments of southwestern Australia

Pink snapper (Pagrus auratus) form spawning aggregations during the austral spring/summer in three adjacent, sheltered, coastal embayments in southwestern Australia (Cockburn Sound, Warnbro Sound and Owen Anchorage). Larval fishes were sampled in these embayments, as well as in the more exposed adjacent waters of Five Fathom Bank, to ascertain which teleost species utilised these areas for spawning concurrently with P. auratus. Obliquely towed bongo nets (500 μm mesh) were used to collect icthyoplankton in November 2007 over three days during the new moon period when spawning of P. auratus is known to peak. A total of 13 270 larvae from 30 teleost families was collected with an overall mean larval fish concentration of 1.91 m -3 (± s.e. 0.28). Larval fish assemblages were significantly different in each of the three embayments and Five Fathom Bank, reflecting the degree of shelter, water-circulation patterns and associated benthic habitats. The highest larval fish concentrations were recorded in Cockburn Sound (3.69 m -3 ± s.e. 0.05) and the lowest along Five Fathom Bank (0.16 m -3 ± s.e. 0.02). P. auratus larvae were only present in samples from the three embayments. The most abundant larvae were those of the Australian anchovy (Engraulis australis), which occurred predominantly in Cockburn Sound and, to a lesser extent, Owen Anchorage. The most ubiquitous larvae included the longspine dragonet (Callionymus goodladi) and leatherjackets (Monacanthidae). This study provides circumstantial evidence that eggs and larvae of P. auratus and other teleosts are retained in the sheltered waters of Cockburn and Warnbro Sounds during spring/summer

Annual, lunar and diel reproductive periodicity of a spawning aggregation of snapper Pagrus auratus (Sparidae) in a marine embayment on the lower west coast of Australia

Ichthyoplankton sampling and ovarian characteristics were used to elucidate whether the reproductive cycles of a spawning aggregation of snapper Pagrus auratus in a nearshore marine embayment were temporally and spatially specific and related with environmental conditions. The reproductive dynamics of this aggregation were studied over four consecutive years (2001-2004). Spawning occurred between September and January each year, when water temperatures ranged from 15·8 to 23·1° C. In all 4 years, the cumulative egg densities in Cockburn Sound were highest when water temperatures were between the narrow range of 19-20° C. The spawning fraction of females was monthly bimodal and peaked during new and the full moons at 96-100% and c. 75%, respectively. The backcalculated ages of P. auratus eggs collected from 16 ichthyoplankton surveys demonstrated that P. auratus in Cockburn Sound spawn at night during the 3 h following the high tide. The spatial distributions of P. auratus eggs in Cockburn Sound during the peak reproductive period in all 4 years were consistent, further implying spawning was temporally and spatially specific. High concentrations of recently spawned eggs (8-16 h old) demonstrated spawning also occurred within the adjacent marine embayments of Owen Anchorage and Warnbro Sound. Water circulation in Cockburn and Warnbro Sounds resembled an eddy that was most prominent during the period of highest egg densities, thereby facilitating the retention of eggs in these areas. The reproductive cycles of P. auratus described in this study have assisted managers with the appropriate temporal and spatial scale for a closed fishing season to protect these spawning aggregations

Rapid lateral extraction of otoliths that maintains the integrity of fish product to improve access to catches and reduce potential sampling biases

The capacity to sample otoliths of fish from commercial, recreational, artisanal or subsistence catches can be constrained if the dissection process results in alterations to their external appearance and thus reduces its value and/or shelf life. There can also be significant biases incorporated into the collection of otolith samples if access is only granted relative to the size of the fish (i.e. if smaller fish are sold whole). To reduce such limitations, we herein describe a rapid and simple method of lateral otolith extraction that maintains the integrity of the fish product, and thus reduces potential biases in sample collection for age structure data. Representative sampling is an important consideration for the collection of age structure data when it is intended to be used in fisheries stock assessments

Similarities between line fishing and baited stereo-video estimations of length-frequency: Novel application of Kernel Density Estimates

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 Choerodon rubescens 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 Epinephelides armatus did not differ significantly between line fishing and stereo-BRUVS. For the sparid Pagrus auratus, 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 P. auratus 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

A preliminary investigation of the potential impacts of the proposed Kwinana Quays development on the commercially and recreationally important fish and crab species in Cockburn Sound. Fisheries Research Report No. 186

Cockburn Sound is the largest of the very few protected marine embayments along the lower west coast of Western Australia. It has been recognised as playing an integral role in the life history strategies of many marine species, including the highly valued snapper Pagrus auratus and blue swimmer crab Portunus pelagicus. Currently, the adult stocks of snapper in the West Coast Bioregion and blue swimmer crabs in Cockburn Sound are at depleted levels, most likely a result of high fishing pressure and below average recruitment in recent years for both species. Due to increasing shipping operations and limited infrastructure the Port of Fremantle will soon be working at capacity. Thus, to alleviate this situation an additional harbour has been proposed in Cockburn Sound, to be located on the eastern margin north of James Point. This outer harbour development has been named ‘Kwinana Quay’. As part of the requirements of the Environmental Protection Agency of Western Australia, the potential impacts of this development on the environment and marine fauna in this embayment need to be assessed. The information provided in this report will aid in the environmental impact assessment to be undertaken by GHD and Oceanica. This report represents a preliminary investigation into the potential impacts of the Kwinana Quay development on commercially and recreationally important fish and crab species. It needs to be considered that this report does not address any broader biodiversity implications. The studies outlined in this report aimed to establish methods useful for assessment and to provide one year of sound quantitative data for future comparisons