Influence of oceanographic environment on the distribution and condition of yellowtail kingfish (Seriola lalandi) within a climate change hotspot

Preferences for environmental conditions fundamentally underpin species' distributions and ecologies. However, shifts in environmental conditions that are consistent with the effects of climate change are increasingly exposing species to conditions that are outside their preferred climate envelope. In response, marine species and communities globally have been affected through changes in 1. geographic distribution, 2. species phenology, 3. ecological interactions and 4. ecosystem structure and dynamics. Although biological responses to environmental change challenges future conservation planning and fisheries management, measured relationships between the environment and ecology for marine species can underpin proactive climate adaptation. This thesis examines the effects of seasonal and longer-term climate-driven oceanographic change on the distribution and body condition of a model coastal-pelagic species, yellowtail kingfish (Seriola lalandi; hereafter 'kingfish'), throughout its eastern Australian distribution. This region is among the most rapidly warming areas of the global ocean, and is used within this thesis as a natural laboratory and early learning location for quantifying and projecting relationships between the environment, distribution and condition of kingfish. Assessing historical biological responses to environmental change and predicting the future effects of continued global change requires an understanding of species' environmental habitat preferences. Species distribution, or habitat suitability, models provide a framework for quantifying species' responses to a suite of environmental variables and for projecting environmental habitat preferences spatially. Here, a habitat model for kingfish from eastern Australia is developed using citizen science data and remotely sensed environmental covariates to assess for historic ('historic analysis') and future ('future analysis') climate-driven changes in the distribution of suitable oceanographic habitat. The optimal model for kingfish oceanographic habitat contained the predictors sea surface temperature, sea level anomaly and eddy kinetic energy, demonstrating that the distribution of kingfish from eastern Australia is driven by simultaneous responses to multiple oceanographic factors. The historical analysis encompassed a 22-year period from 1996 to 2017 and revealed that rapid poleward shifts in the core (94.4 km/decade) and poleward edge (108.8 km/decade) of kingfish oceanographic habitat have occurred off eastern Australia over this period. This analysis accounted for the effects of natural intra-and interannual climate variability, suggesting that the rate and magnitude of these distributional shifts is likely due to human-induced environmental change. These methods and results demonstrate the utility of marine citizen science data for quantifying climate-driven redistributions, but necessitates shifting focus from species distributions directly, to the distribution of species' environmental habitat preferences. The future analysis used dynamically downscaled oceanographic variables to assess for changes in the temporal persistence (months per year) of suitable kingfish oceanographic habitat within south-eastern Australia's six coastal bioregions between 1996 and 2040. This analysis identified that a decline in temporal habitat persistence is predicted for the northernmost (equatorward) bioregion, whereas increases are predicted for the three southernmost (poleward) bioregions. Furthermore, temporal habitat persistence is shown to be an important metric for potential climate change adaptation, particularly when predicted at near-term decision-making time-scales, because it provides fishery-relevant information (i.e. a measure of fishing opportunity). This analysis demonstrates how novel metrics relevant to climate adaptation can be derived from projections of species' environmental habitats, and are appropriate for the management of fisheries resources and protection of high conservation value species under future climate change. While habitat models are commonly used to estimate a species' probability of occurrence, they have not been used to examine the effect of environmental habitat suitability on fish condition, which is considered to be an integrated measure of physiological status. Bioelectrical impedance analysis (BIA) has emerged as a rapid, nonlethal and cost-effective method for measuring fish condition and can provide data that are suitable for comparison with habitat models. While BIA has a history of application in medical fields, it is a relatively novel tool in fish and fisheries research requiring consideration of potential sources of error to ensure robust and comparable data are obtained. In light of this, the effects of five factors related to fish handling on an instantaneous body condition index (phase angle) were experimentally tested. These experiments identified significant effects of time since death, temperature of the tissue, removal of the gills and gastrointestinal tract, and the anatomic location for measurements on BIA measurements. Results were used to develop a protocol for the field-based application of BIA to control for potential measurement error associated with variable fish handling procedures. Adhering to the aforementioned protocol, the body condition of 113 kingfish from southeastern Australia were measured using BIA over three consecutive austral summer‚Äö-autumn periods (2016/17‚Äö-2018/19). These data were compared to modelled oceanographic habitat to 1. test whether individuals sampled from areas of high‚ÄövÑv™quality habitat were in better condition than individuals sampled from areas of low‚ÄövÑv™quality habitat, and 2. assess whether the condition of kingfish responded to oceanographic habitat suitability predicted at varying time‚ÄövÑv™before-capture periods. Oceanographic habitat suitability was found to be significantly correlated with kingfish condition at time‚ÄövÑv™before‚ÄövÑv™capture periods ranging from one to four weeks and became increasingly correlated at shorter lead‚ÄövÑv™times. These results highlight that 1. fish condition can respond sensitively to environmental variability and this response can be detected using oceanographic habitat suitability models, and 2. climate change may drive extensions in species range limits through spatial shifts in oceanographic habitat quality that allow individuals to persist beyond historical range boundaries without their body condition being compromised. The results of this thesis emphasise that strong relationships can exist between the environment, distribution and condition of pelagic fishes. This body of evidence highlights the value of environmental variables as proxies for the distribution and condition of pelagic fishes and supports climate change adaptation strategies that are underpinned by correlative species-environment relationships. However, it remains considerably uncertain whether known biological responses to environmental variables can be extrapolated to novel regions or time periods. Transferability is a particularly important consideration when using established relationships between species and their environment to forecast the future ecological effects of climate change and develop adaptation strategies. Where data allows, a mechanistic understanding of species responses to environmental variables should be considered alongside correlative relationships to improve the robustness of species-environment relationships to the novel environmental conditions that biodiversity will inevitably face in a rapidly changing world.