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The fish faunas of estuaries in the Albany region of south-western Australia

Krispyn, Kurt N. (2021) The fish faunas of estuaries in the Albany region of south-western Australia. Honours thesis, Murdoch University.

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Estuaries are amongst the most productive ecosystems and act as important nurseries and habitats for aquatic fauna. Microtidal estuaries (tidal range <2 m) are particularly prone to climate change, the effects of which on fish communities and future predictions on their state under climate change are not well understood, especially for small estuaries (<1 km2). This study quantitatively determined the fish fauna in the nearshore and offshore waters of eight microtidal estuaries (including six <1 km2) with varying extents of connectivity to the ocean in the Albany region of south-western Australia. It investigated whether fish faunas were influenced by region, season, “bar status” (i.e., open or closed), and physico-chemical variables. Nearshore waters (<1.5 m) were sampled with four replicate 21.5 m seine nets in each region (lower, basin and upper) in each estuary over four seasons in 2020. Offshore waters (>1.5 m) were sampled using four 160 m composite gill nets set throughout each estuary in the same four seasons. Conductivity and temperature loggers were used to detect any breaches of the sand bar that occurred between sampling occasions. Fish faunas in nearshore and offshore waters were m different among estuaries, and across seasons and regions in shallower waters, although all estuaries were dominated by the same suite of core species. Diversity and faunal composition were highly influenced by salinity and the duration of ocean connectivity. Diversity increased with salinity due to the immigration of marine species up until hypersaline conditions (>50) occurred, however, when salinities exceeded 100 for a protracted period, only a single highly euryhaline estuarine species survived. Permanently-open estuaries, i.e., Oyster Harbour and Waychinicup Estuary, contained the greatest number of species, but lower densities (nearshore) and catch rates (offshore) than those estuaries that open at least once a year, i.e., Torbay, Taylor, Normans and Cheyne inlets and Cordinup River. The normally-closed and extremely hypersaline Beaufort Inlet was depauperate and, after autumn, no fish were recorded in offshore waters with only a single atherinid species occurring in nearshore waters. This study provides baseline information for these data-poor estuaries and identified one system of high conservation significance. It also provides insights on how estuaries and their fish fauna may change due to reduced rainfall and river flow associated with climate change, and become more like Beaufort Inlet.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
Supervisor(s): Tweedley, James and Loneragan, Neil
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