Movement and population connectivity of blue salmon catfish Neoarius graeffei in the Clarence River, New South Wales Australia: implications for river development

    Research output: ThesisDoctoral Thesis

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    Abstract

    Fish move at different life stages throughout a range of habitats for the purposes of feeding, reproduction or seeking shelter. The scale and complexity of these movements can vary among individuals and species, and understanding fish movement is essential to interpreting the complexities of population dynamics. Movement patterns can be grouped depending on their requirements to access freshwater, estuarine and marine habitats which can be defined as diadromous, anadromous, catadromous and other accepted categories. Coastal free-flowing rivers provide access to productive freshwater, estuarine and marine habitats and, as such, support a diversity of life history strategies. The development of coastal rivers via the construction of dams can be particularly detrimental to fish species that require both fresh and saltwater habitats to complete their life history. Since the 1950s, the Clarence River, a coastal river in northern New South Wales, Australia, has been a recurring candidate for river development to mitigate flooding and address water security issues. However, relatively little is known about the migratory habits of fish in this system and the potential impacts of such river development. This thesis aims to bridge some of these knowledge gaps and provide an understanding of the movement ecology and habitat use of an abundant native fish species within the Clarence River Basin. I took a multiple lines of evidence approach by combining the complementary methods of biotelemetry, water chemistry and otolith microchemistry to establish an understanding of connectivity in the Clarence River Basin. My focal species was the blue salmon catfish Neoarius graeffei, an abundant and adaptable, yet not well understood, ariid catfish species which is distributed throughout northern Australia and Papua New Guinea.
    Trace metals and 87Sr:86Sr in surface water from 59 sites in the Clarence River Basin were used to assess spatial variation with the aim being to compare surface water chemistry with otolith microchemistry to infer movement patterns in fish. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and strontium chromatography identified that strontium and barium varied spatially, which was driven by the underlying surface geology, as well as the tidal influence throughout the lower Clarence River estuary. The level of differentiation identified in the current study has the potential to enable detection of fish movements among estuarine, interior and outer edge areas of the basin via the use of otolith analysis, with fine-scale movements best elucidated using complementary techniques, such as acoustic telemetry.
    I used acoustic telemetry to understand fine-scale fish movement and to quantify abiotic stimuli in relation to seasonal movement patterns in N. graeffei throughout the lower Clarence River Basin. All tagged fish remained within the lower sections of the Clarence River for the duration of the one-year study and confined themselves mostly to estuarine reaches, with occasional movement into freshwater habitats. Seasonal differences in habitat occupation were observed, with N. graeffei using habitats close to the river mouth in winter and upstream estuary habitats in spring. Broad-scale movement patterns were influenced by both water temperature and river flow. Sex-specific differences in seasonal habitat use were observed, which is likely linked to contrasting energetic investment in reproduction.
    Otolith microchemistry was then used to understand the lifetime movement patterns of N. graeffei in the Clarence River Basin, using otolith microchemistry. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) was used to quantify Sr:Ca, Ba:Ca and 87Sr:86Sr ratios from 72 adult fish. Variation was observed in the movement patterns of individual N. graeffei, although a strong association with the estuarine reaches evident among most individuals. Movement into freshwater habitats further upstream for extended periods was observed for a subset of individuals. This study highlights partial migration within movement patterns in N. graeffei, emphasising the importance of both freshwater and estuarine habitats for the species.
    Together, these studies provide a baseline understanding of how an abundant species, such as N. graeffei, utilises estuarine and freshwater habitats within a free-flowing coastal river, and how environmental factors such as temperature and river flows influence patterns of movement and connectivity. The findings suggest that N. graeffei is an estuarine resident that can complete its lifecycle within the confines of the tidal limit but can also opportunistically utilise freshwater habitats. Given the acoustic telemetry results from Chapter 3 found that N. graeffei did not leave the Clarence River, the current assumption is that little to no genetic dispersal exists between rivers. Additionally, due to time constraints of the thesis program, genetic studies to understand broader dispersal between rivers could not be completed. Otolith analysis revealed partial migration, with varying movement patterns between chemically different areas. Water chemistry analysis revealed a distinctive difference between estuarine areas and the rest of the basin, along with some distinct differences in the northern and southern limits. The findings suggest that N. graeffei are estuarine residents capable of completing their lifecycle within the confines of the tidal limit, yet they also utilise freshwater habitats. Additionally, they occupy habitats seasonally within the Clarence River system, indicating limited population mixing between coastal rivers.
    This study not only provides insights into the movement ecology of an ariid catfish species in a sub-tropical river but also raises broader implications for the conservation and management of estuarine and freshwater ecosystems worldwide. By demonstrating the importance of combining multiple methods to understand movement in a coastal river system, this research lays the foundation for future studies that aim to elucidate the complex interactions between aquatic species and their environments. Furthermore, the completion of the first baseline water chemistry analysis of a south-eastern Australian coastal river represents a significant contribution to global freshwater research efforts where isotopic databases are limited. These findings underscore the necessity of comprehensive interdisciplinary approaches in addressing the challenges of aquatic ecosystem conservation and management in the face of environmental change.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • Charles Sturt University
    Supervisors/Advisors
    • Baumgartner, Lee, Principal Supervisor
    • Doran, Gregory, Co-Supervisor
    • Thiem, Jason, Co-Supervisor
    Award date02 Aug 2024
    Place of PublicationAustralia
    Publisher
    Publication statusPublished - 05 Aug 2024

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