Burdon, FrankKahotea, Josette2026-06-022026-06-022026https://hdl.handle.net/10289/18314Wetlands are widely valued in conservation and restoration, yet their ecological role when connected to lakes is often misunderstood in the management of freshwater fish. Rather than functioning simply as hydrological buffers for lake catchments, wetlands may serve as critical refugia for native fishes under increasing pressure from climatic variability and invasive predators. I investigated whether the spring-fed Millar Road Wetland (MRW), located on the margin of Lake Ōkāreka (Rotorua Te Arawa Lakes, Aotearoa), supports a persistent population of kōaro (Galaxias brevipinnis Günther, 1866). A key objective of my research was to examine the mechanisms underpinning the potential refuge function of the wetland. By integrating year-round population monitoring, mark–recapture analysis, environmental modelling, and stable isotope analysis, I assessed demographic stability, predator limitation, and trophic structure of kōaro in this habitat. The MRW supported a resident, multi-cohort kōaro population exhibiting seasonal recruitment, positive allometric growth, and stable body condition across years. Mark-recapture data indicated close site fidelity and continued individual growth, while interannual comparisons demonstrated stable adult size structure despite evidence for variable juvenile recruitment. Other notable members of the MRW community included common bullies (Gobiomorphus cotidianus McDowall, 1975) and kōura (Paranephrops planifrons White, 1842). Although juvenile rainbow trout (Oncorhynchus mykiss Walbaum, 1792) appear to enter the wetland periodically, their occurrence was spatially restricted to upstream areas and may be strongly mediated by hydrological connectivity. Episodic dissolved oxygen minima and shallow, structurally complex habitat likely constrain trout residency and growth, while kōaro were able to persist in the wetland across seasons. Stable isotope analysis revealed strong trophic differentiation: kōaro were supported predominantly by allochthonous carbon, largely via detritivorous aquatic insects, whereas common bullies relied on autochthonous benthic production. I hypothesised that this energy-channel partitioning of the food web reduces exploitative competition and helps explain the coexistence of these two native fish species at relatively high densities. Together, these findings suggest that the role of the MRW as a refuge emerges not from absolute predator exclusion, but from a locally-dependent balance between hydrological connectivity, environmental filtering, habitat structure, and trophic organisation. Connectivity in the wetland is both essential and risky: it sustains demographic exchange with the lake whilst periodically permitting an invasive, non-native predator access, yet environmental harshness limits sustained trout establishment, and asymmetric tolerances allow kōaro to persist. In a climate-sensitive species such as kōaro, the persistence of a robust wetland population highlights the potential importance of small, groundwater-fed systems as dynamic refugia within invaded landscapes. Protecting and restoring similar wetlands may therefore play a critical role in safeguarding native freshwater biodiversity under ongoing climatic and hydrological change in Aotearoa.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.koaroGalaxias brevipinnisrefugewetlandThesis