School of BioSciences - Theses

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    Individual movement and environmental context influence growth rates of a mobile freshwater fish
    Barrow, Joshua Samuel ( 2021)
    An individual’s growth rate is a key determinant of its body size, which is in turn intrinsically linked to its fitness through reproduction and survival, and population-level processes such as recruitment. As individuals move, they experience different environmental conditions which can impact on the resources available for growth. Indeed, animals may track favourable conditions through space and time to maximise resource acquisition and thus growth. Despite the benefits, movement behaviours can vary among life stages and among individuals, with some individuals remaining resident in their natal environment. The persistence of different movement phenotypes within a population, known as partial migration, suggests that multiple phenotypes can have commensurate benefits. The degree to which movement and environmental context influence an individual fish’s growth rate at different life stages remains poorly understood. In this thesis, I use growth and movement information naturally archived in golden perch (Macquaria ambigua) otoliths (‘ear stones’) from across the Murray-Darling Basin to address key questions about the relationships between growth, movement, and variation in environmental conditions. First, does early life growth influence survival later in life? Second, does the presence and direction of movement relative to river discharge affect growth rates? Last, does knowledge of the locations inhabited by individuals throughout their lives increase the performance of fish growth models? I found that faster early-life growth (over first 30 days of life) increased the survival of stocked fish to two years of age. Wild-born individuals that moved among river reaches had faster growth over the first eight years of life compared to those that remained resident. Differences in juvenile growth rates were, however, dependent on movement direction, with increased growth of downstream dispersers, upstream dispersers, and hatchery stocked fish compared to resident individuals. The impact of environmental conditions on golden perch growth was modulated by an individual’s life stage and its movement type. Including the environmental conditions experienced by an individual throughout their life, however, did not improve the performance of growth models. Instead, environmental conditions at a fixed location (location of capture) were sufficient to explain annual growth variation in golden perch, even if they had undertaken extensive movements across their lifetime. I suggest that for highly mobile fish such as golden perch, coarser environmental conditions may be more important in governing annual growth. Growth displayed complex relationships with hydrology, that were dependent on location and life-stage. Generally, there were positive associations between increased river discharge in summer and spring and golden perch growth, although high discharge limited growth in young and vulnerable fish in early-life stages. I suggest that effects of river discharge on individual growth manifests through a combination of high velocities impacting movement energetics (upstream or downstream), feeding behaviours of young fish, and stimulating productivity pulses in the river system, increasing habitat and food availability. My thesis contributes valuable information on native fish ecology. I quantify how movement patterns and environmental conditions influence growth at multiple life stages and discuss how the presence of multiple phenotypes can bolster the resilience of populations to environmental disturbance. I expect this thesis to inform the management of freshwater fish, one of the most threatened groups of vertebrates on the planet, through improved stocking outcomes and understanding of the impacts of managed discharge regimes and the importance of connectivity.