Author Identifier
Paige Wilson: http://orcid.org/0000-0003-1041-4138
Date of Award
2026
Document Type
Thesis
Publisher
Edith Cowan University
Degree Name
Master of Science by Research
School
School of Science
First Supervisor
Anna Hopkins
Second Supervisor
Quinton Burnham
Third Supervisor
Pierre Horwitz
Abstract
The wetland ecosystems of far southwestern Australia face multiple threats including land clearing, historical cattle grazing, changed hydrology, extensive groundwater extraction, and changed fire regimes. Each is exacerbated by a drying climate, and together they provide a significant challenge to the on-going survival of the freshwater fish in this region particularly fish that are endemic, range restricted, and therefore, more likely to be more vulnerable. This study focuses on three such species: Galaxiella munda, Galaxiella nigrostriata and Lepidogalaxias salamandroides, the latter two of which are known to aestivate.
In order to make conservation decisions regarding management of wetlands for the continued survival of these freshwater fish species, we need to know exactly where in wetlands, and in which specific habitats, the study species occur. This is particularly so since previously used fish capture methods have been relatively indiscriminate at the habitat scale. Using the acid peat flats of D'Entrecasteaux National Park as a study location, the specific aim of this study was to characterise the distribution of the fishes within their natural habitat and use this information to determine how disturbance may be impacting their viabilities.
The thesis investigates how conventional trapping methods and Environmental DNA (eDNA) data can provide information on the best methods of species detection, as well as determining if eDNA is suitable to be used in an acidic aquatic environment. A total of 23 sites within a wetland system in the Windy Harbour area were examined, with most fish data collected at critical water level times – highest in late winter, and later in spring as water levels receded. At each site physico-chemical and habitat variables were also collected.
Box trapping, sweep netting and eDNA were all found to be effective methods for detecting the presence of the three study species. Sweep netting was the most effective method with the most occurrences at sites, but box traps caught a higher number of fish. The eDNA method was more effective for G. nigrostriata and G. munda. eDNA enabled the detection of L. salamandroides but less reliably, possibly because it is benthic dwelling and water samples were taken from the water column, so sample collection methods would need further consideration. eDNA is a useful tool in determining where the three study species are within their environment, however, there remain limitations around population structures for fishes using this method, suggesting it would be beneficial to use eDNA in conjunction with conventional trapping methods. Conventional methods will continue to have value particularly for establishing population densities and determining population structures. All methods tested should not be used for absence monitoring until confidence levels in their use can be determined.
An attempt was made to determine habitat associations for the three study species according to where the study species were (and weren’t) detected. Galaxiella nigrostriata was more likely found in wetlands characterised by a low pH, highly tannin-stained water and a degree of connectivity between other wetlands within the area. The degree of water permanence is also a consideration for the survival of the fish. Lepidogalaxias salamandroides occurrence was strongly seasonal, found in deeper waters, in Restionaceae sedge dominated wetlands. G. munda was only found in a flowing creek where water was clear and less acidic. Further research would be needed to determine additional specific habitat variables relating to the three species.
Ways to improve the effectiveness of eDNA sampling, such as the use of passive sampling for benthic dwelling fish, and sampling (filtering) larger volumes of water in the field during peak water levels in winter, are outlined. These improvements to sampling methods will also enable further refinements to determining microhabitat characteristics for the three species. The study has pointed to particular habitats of interest which will need further investigation, such as the use of Taxandria juniperina dominated swales for breeding and refuge for G. nigrostriata and L. salamandroides, and the impacts of fire. The thesis concludes with recommendations for conservation and management of the three species of fish. The importance of maintaining hydrological connectivity in wetlands of the Windy Harbour area, including considerations of the impacts of road and track formation, and ground water abstraction, is highlighted. Careful attention to the timing of prescribed burns is recommended to minimize risks to aestivating species. The use of eDNA for early detection of invasive species is also recommended, and will require further testing of eDNA efficacy in acidic and organic-rich environments.
Recommended Citation
Wilson, P. R. (2026). Detecting habitat use of three endemic freshwater fish of far southwestern Australia. Edith Cowan University. https://doi.org/10.25958/erjc-v939