Material model calibration for superplastic forming

Superplastic forming is a slow forming process. The forming time can be minimized by optimizing the pressure profile applied to the forming sheet. The optimization of the superplastic forming pressure is usually done such that a target strain rate at a high strain rate sensitivity is maintained. Careful consideration of the strain rate is required, since localized thinning can occur when the material is strained too quickly. This paper demonstrates that it is essential to explicitly include strain rate sensitivity data, obtained from strain rate jump tests, during the calibration of material model used for superplastic forming simulations. Conventional calibration methods only consider stress–strain data at different strain rates. Such an approach implicitly assumes that a material model that matches the stress–strain data at the different strain rates, will automatically match strain rate sensitivity data. However, by explicitly including the strain rate sensitivity data, the selected material model is more susceptible to localized thinning as the applied strain rate is increased. It is essential for the selected material model to exhibit this behaviour to prevent superplastic forming simulations at high strain rates from predicting stable deformation, when in fact localized thinning will occur.http://www.tandfonline.com/loi/gipe202019-07-03hj2018Mechanical and Aeronautical Engineerin

Unexpected survival of sharptooth catfish Clarias gariepinus (Burchell 1822) during acute rotenone toxicity trials will complicate management of invasions

The sharptooth catfish Clarias gariepinus is an emerging global invader for which control strategies might include the use of piscicides such as rotenone. Experimental exposure demonstrated that C. gariepinus was less susceptible to rotenone than most other fish species, with unexpected survival observed at rotenone concentrations of 87.5 and 100 lg L-1. C. gariepinus were also observed exhibiting avoidance behaviour to rotenone treated water and were found to be capable of recovering from rotenone exposure. As such, effective eradication might not be attainable even at a dose exceeding 100 lg L-1 with exposures of longer than 24 h. This exposure scenario may pose an unacceptable risk to non-target fauna and highlights the difficulty associated with managing current and future invasions

Optimising invasive fish management in the context of invasive species legislation in South Africa

South Africa hosts a large number of non-native freshwater fishes that were introduced for various industries. Many of these species are now listed under the National Environmental Management: Biodiversity Act (NEM:BA) Alien and Invasive Species (A&IS) lists and regulations, though the practical options available to conservation agencies to effectively manage these fishes vary greatly among species and regions. Objectives & methods: We assessed the history and status of national legislation pertaining to invasive freshwater fishes, and the practical implications of the legislation for managing different species with contrasting distributions, impacts and utilisation value. Results: The smallmouth bass, despite being a potential conflict-generating species, is fairly straightforward to manage based on current legislation. Two species of trout, which remain absent from the NEM:BA A&IS lists because of ongoing consultation with stakeholders, continue to be managed in regions like the Western Cape province using existing provincial legislation. To maximise the limited capacity for management within conservation agencies, we proposed a decision-support tool that prioritises invasive fish populations that represent high environmental risk and low potential for conflict with stakeholders. Using three case studies, we demonstrated how the tool can be used to set management goals of 'eradicate', 'manage against impacts and further spread' and 'continue to monitor population' as the most pragmatic solutions given the state of an invasion, its socio-economic impact and the capacity of the responsible agency to act. Conclusion: By choosing a pragmatic management strategy, conservation agencies can maximise the effective deployment of limited resources, while minimising avoidable conflicts with stakeholders.EM201

Rethinking refuges: Implications of climate change for dam busting

Climate change is projected to alter river discharge in every populated basin in the world. In some parts of the world, dam removal now outpaces their construction and the diminishing cost efficiency of dams in drying regions is likely to further increase the rate of removals. However, the potential influence of climate change on the impact of dam removals has received almost no consideration. Most dams have major biological and ecological impacts and their removal would greatly benefit riverine ecosystems. However, using model regions in the Southern Hemisphere, we highlight that artificial lentic habitats created by dams can act as refuges for increasingly imperiled freshwater fishes, and dams may also prevent the upstream spread of invasive alien species in rivers. We argue that, in these and other regions where the major impact of climate change will be to reduce streamflow and aquatic refuge availability, a shifting balance between the negative and positive environmental impacts of dams requires policy makers to include climate change predictions in prioritisation processes for dam remova

Vulnerability of Cape Fold Ecoregion freshwater fishes to climate change and other human impacts

1. Native freshwater fish populations throughout South Africa's Cape Fold Ecoregion (CFE) are in decline as a result of human impacts on aquatic habitats, including the introduction of nonnative freshwater fishes. Climate change may be further accelerating declines of many species, although this has not yet been studied in the CFE. This situation presents a major conservation challenge that requires assigning management priorities through assessing species in terms of their vulnerability to climate change. 2. One factor hindering reliable vulnerability assessments and the concurrent development of effective conservation strategies is limited knowledge of the biology and population status of many species. This paper reports on a study employing a rapid assessment method used in the USA, designed to capitalize on available expert knowledge to supplement existing empirical data, to determine the relative vulnerabilities of different species to climate change and other human impacts. Eight local freshwater fish experts conducted vulnerability assessments on 20 native and 17 non‐native freshwater fish species present in the CFE. 3. Results show (1) that native species were generally classified as being more vulnerable to extinction than were non‐native species, (2) that the climate change impacts are expected to increase the vulnerability of most native, and some non‐native, species, (3) that vulnerability hotspots requiring urgent conservation attention occur in the Olifants‐Doring, upper Berg and upper Breede River catchments in the south west of the region, (4) that in addition to providing guidance for prioritizing management interventions, this study highlights the need for reliable data on the biology and distribution of many CFE freshwater fishes, and (5) that identification of priority areas for protection should be based on multiple sources of data

The SARAO MeerKAT 1.3 GHz Galactic Plane Survey

We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251○ ≤l ≤ 358○ and 2○ ≤l ≤ 61○ at |b| ≤ 1 5). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8″ and a broadband RMS sensitivity of ∼10–20 μJy beam−1. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908–1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE H II region candidates are not true H II regions; and a large sample of previously undiscovered background H I galaxies in the Zone of Avoidance

Protected areas and endemic freshwater fishes of the Cape Fold ecoregion : missing the boat for fish conservation?

CITATION: Jordaan, M. S., Chakona, A. & Van der Colff, D. 2020. Protected areas and endemic freshwater fishes of the Cape Fold ecoregion : missing the boat for fish conservation? Frontiers in Environmental Science, 8:502042, doi:10.3389/fenvs.2020.502042.The original publication is available at https://www.frontiersin.org/journals/environmental-scienceFreshwater systems and their associated biodiversity are among the most threatened ecosystems globally. The greatest threats to freshwater fishes are the introduction and spread of non-native species, pollution, habitat degradation and loss, and overexploitation. While many regions across the world contain extensive networks of protected areas, these are largely ineffective for protecting riverine systems and their biodiversity. This is because they were designed with the aim of prioritising conservation of terrestrial biodiversity, with limited or no consideration for aquatic systems. The Cape Fold Ecoregion, located within the Western and Eastern Cape Provinces of South Africa, is home to the highest percentage of threatened freshwater fishes in the country. The region has an extensive protected area network that protects a wide array of ecosystems, but limited information exists on the role of protected areas in conserving the endemic freshwater fish fauna of this region. This study evaluated the value of protected areas for protection of freshwater fishes in the Western Cape Province by setting species conservation targets and then intersecting species distribution data with protected area polygons. Conservation targets were set to protect the minimum viable population required for long-term persistence, with a minimum of 10 subpopulations as a target. This, along with other factors such as population viability and protected area effectiveness was used to determine whether a species was effectively protected by the current protected area network. Species were classified into one of four categories; (1) "well protected," (2) "moderately protected," (3) "poorly protected," and (4) "not protected." Our results indicate that the majority of native fishes are inadequately protected within the current protected area network in the province. This is mainly a result of the linear nature of riverine ecosystems that exposes them to impacts and threats that emanate from outside of the protected area. These limitations are not unique to the CFE, and our findings have broader implications as they highlight the need for integrating both the riverine and terrestrial ecosystems in the design, expansion and management of protected areas. This will enhance and maximise conservation and protection of riverine systems and their unique biodiversity.Publisher's versio

Determining the minimum effective dose of rotenone for eradication of alien smallmouth bass Micropterus dolomieu from a South African river.

African Journal of Aquatic ScienceIn February 2012 the Rondegat River, in the Cape Floristic Region, was the first river in South Africa where the piscicide rotenone was used to remove an alien invasive fish, smallmouth bass Micropterus dolomieu. In preparation for this treatment, the sensitivity of smallmouth bass to various concentrations of the rotenone formulation CFT Legumine (5% active rotenone) was evaluated a week prior to treatment using standard toxicity tests to determine the minimum effective dose (MED) that would result in 100% mortality after exposure for 4 h. The MED was 0.0125 mg l-1 rotenone. Adverse effects, including erratic swimming, loss of equilibrium and death, occurred in a dose-dependent manner with smaller fish responding faster than larger ones. Standard operating procedures for the use of rotenone recommend treatment at a minimum of twice the calculated MED. Given the uncertainty associated with rotenone losses through hydrolysis and photolysis under field conditions, and the possible occurrence of smallmouth bass more tolerant than those tested, a concentration of twice the recommended treatment dose (0.050 mg l-1 rotenone) was finally used to treat the Rondegat River for a duration of 6 h.Cape nature National Research Foundation Water research Commissio

Acute and sublethal effects of sequential exposure to the pesticide azinphos-methyl on juvenile earthworms (Eisenia andrei)

The use of organophosphate pesticides is an integral part of commercial farming activities and these substances have been implicated as a major source of environmental contamination and may impact on a range of non-target fauna. The extent to which soil dwelling non-target organisms are affected by exposure to the organophosphate azinphos-methyl was investigated through monitoring selected biomarker responses and life cycle effects under laboratory conditions in the earthworm Eisenia andrei. Standard acute toxicity tests were conducted followed by a sequential exposure regime experiment, in order to assess the effects of multiple pesticide applications on biomarker (cholinesterase activity and neutral red retention time), life-cycle (growth and reproduction) and behaviour (avoidance and burrowing activity) responses. The present study indicates that the time between exposure events was a more important variable than concentration and that a longer interval between exposures may mitigate the effects of pesticide exposure provided that the exposure concentration is low. Additionally, it was shown that E. andrei was unable to avoid the presence of azinphos-methyl in soil, even at concentrations as high as 50% of the LC 50 value, indicating that the presence of azinphos-methyl in the soil pose a realistic threat to earthworms and other soil dwelling organisms. The ChE inhibition test showed a high percentage inhibition of the enzyme in all exposure groups that survived and NRR times of exposed organisms were lower than that of the controls. The present study yielded important results that contribute to the understanding of biological impacts of pesticide pollution on the environment. Extrapolating these results can aid in optimising pesticide application regimes to mitigate the environmental effects thereof and thus ensuring sustained soil biodiversity in agricultural areas. © 2011 Springer Science+Business Media, LLC

Analysis of active rotenone concentration during treatment of the Rondegat River, Cape Floristic Region, South Africa: evaluation of the Minimum Effective Dose (MED).

Most endemic freshwater fish species of the Cape Floristic Region are listed as threatened, due mainly to the impacts of invasive alien fish species. The piscicide rotenone has been identified as a potential tool to aid the conservation of indigenous species through the removal of invasive fish. Rotenone was used in the Rondegat River, Cederberg, where smallmouth bass Micropterus dolomieu had extirpated the indigenous fish. An initial rotenone treatment in March 2012 was followed by another in March 2013. Due to concerns following the first treatment about possible build-up of rotenone between treatment stations, the second treatment included monitoring of rotenone concentrations during the treatment. Measured concentrations were consistently below the selected treatment concentration of 37.5 μg l−1 and dropped to below the tested effective piscicidal concentration of 12.5 μg l−1 at some sampling points. There was no build-up of rotenone within the treatment zones, but rotenone took longer than expected to clear out of the treatment area. The rotenone was effectively neutralised when the neutralisation station was operational, but was still detectable after neutralisation was terminated.CapeNature, NRF, SAIA