Browsing by Author "Walsh, C"

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    Isotopic tools for better management of aquatic environment and resources
    (Australasian Environment Isotope Conference, 2015-07-08) Mazumder, D; Saintilan, N; Kobayashi, T; Wen, L; Rogers, K; Hollins, SE; Johansen, MP; Walsh, C; Narimbi, J; Sammut, J
    Water is a vital resource that is under ever-increasing demand from population and industry growth, agricultural development, and environmental allocations that are crucial to sustain the natural ecosystems upon which we all rely. Analysis of naturally-occurring stable isotopes (d13C and d15N) have emerged as powerful techniques for addressing research and management-related questions in ecology and aquaculture. Our work on coastal wetlands has identified carbon and nutrient dynamics, the sequestration potential of saltmarsh and mangrove systems, and anthropogenic impacts on aquatic food chains. We compared trophic position and dietary sources in freshwater wetlands during a severe El Nino drought (2007) and following a subsequent series of wetter than average La Nina years (2013), and identified that food chains expand and contract with oscillations in climate phase in the absence of new sources of carbon. We applied isotopic tools in aquaculture, which is the fastest growing food-producing sector in Australia and around the world and accounts for one-third of global fish production. However, production and profitability from inland and coastal aquaculture are often low due to environmental constraints and the increasing cost of production. Our work to develop low-cost feeding strategies for PNG fish farmers suggests operational costs can be reduced by carefully utilising production inputs or changing the ingredients used in feed formulations. These results provide insights for further applications of stable isotopes in the aquatic ecosystem studies.
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    A multi-faceted approach for evaluating fishway performance in south-eastern Australia
    (University of Massachusetts Amherst, 2015-06-24) Walsh, C; Duncan, M; Paull, T; Reinfelds, IV; Mazumder, D; Giligan, D
    In the coastal rivers of south-eastern Australia 70% of fish migrate at some stage between the rivers and estuary to complete their life cycle, predominantly as catadromous and amphidromous migrations. A major threat to diadromous fishes in this region is the construction of artificial barriers, such as dams, weirs and road crossings. Traditionally, fishways in Australia were based on those designed to pass salmonids, thus limiting fish passage for the comparatively poorly swimming Australian native species. However, in the past few decades fishway design has been refined to accommodate native species’ swimming ability and wide range of body sizes (40- 1000mm). Ongoing monitoring programs have facilitated the refinement of modern fishway design to ensure successful passage of the target community. The Hawkesbury-Nepean and Shoalhaven rivers are the second and fifth largest regulated coastal river systems within the state of New South Wales. Barriers in these systems were retrofitted with either vertical slot or high-dam fishways completed over the last six years, together with new environmental flows. Sampling techniques for fishway evaluation on these rivers includes monitoring fish communities above and below the barrier; PIT tagging to assess timing of migration through fishways; and fishway entrance and exit trapping to assess the success of the fishway at passing individual species. Modern sampling techniques such as genetics and stable isotope analysis (SIA) are also being used on historically fragmented habitats to detect changes in population genetic structure and trophic shifts. Finally, analysis of fish movement (derived via acoustic telemetry) in response to environmental variables is providing detailed information on potential migration cues and flow regimes required to stimulate fish movement. This multi-faceted research approach not only provides empirical and real-time data for evaluating the performance of fishways in improving fish passage, but also informs operational managers on their efficiency and assists engineers in refining future fishway design.
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    Stable isotope (δ13C and δ15N) studies in aquatic ecosystems: response to different conditions
    (The University of Western Australia, 2013-07-10) Mazumder, D; Walsh, C; Williams, RJ; Jenkins, K; Sives, C; Hollins, SE; Meredith, KT; Doyle, T
    Rivers and wetlands are complex ecosystems with numerous relationships between water, earth, air, plants and animals. The stable isotopes 13C and 15N were investigated in river and wetland ecosystems to evaluate food web structure complexity, with particular emphasis on their response to changing hydrological conditions. A study developed on the Shoalhaven River focused on assessing the differences in trophic conditions of fish populations found above and below Tallowa Dam. Some species displayed little variation in C or N signatures over the two years sampling period suggesting a preferential dietary niche, regardless of hydrological or density-dependent conditions. The variable diet sources between Australian bass revealed by source mixing calculation also indicated trophic discontinuity within these restricted environments. We found variable trophic levels and sources for the same species of invertebrate and fish between habitats in wetlands show the effect of divergent ecological conditions and landuse practices. For example, in the Macquarie Marshes we found that an extended inter-flood interval caused the decline of riparian vegetation communities including river red gum signalling a shift from aquatic floodplain ecosystems to terrestrial ecosystems where grasses and chenopod shrubs dominate as an organic carbon source. Results provide insights into stable isotope use to better understand potential impacts of future climate variation on river and wetland systems.