Abstract
The Vasse-Wonnerup wetland is an ecologically important area for birds and is listed as a 'Wetland of International Importance' by the Ramsar Convention. However, despite extreme eutrophication, regular algal blooms and large fish kills, most recently in April 2013, almost no faunal research has been undertaken. This poster and presentation details the spatial characteristics of the fish fauna of seven regions of the estuary, each of which differ in their environmental characteristics and illustrates how they change through the year as salinity changes. For example, the Lower Vasse River Wetland (LVRW) remains entirely freshwater all year, while the Vasse and Wonnerup Estuaries fluctuate seasonally from freshwater (~0) to markedly hypersaline (~80) and the Deadwater and Wonnerup Inlet remain marine. Species richness and fish density were the highest in the marine areas (Deadwater and Wonnerup Inlet) and lowest in the LVRW during all seasons. No species were recorded in the upper Vasse and Wonnerup estuaries in summer and autumn due to the very high salinities and shallow waters. The fish fauna differed markedly among most regions, with the biggest differences occurring between the marine areas and the LVRW. The fish in the former regions were dominated by estuarine species, i.e. the Elongate Hardyhead (Atherinosoma elongata), Black Bream (Acanthopagrus butcheri) and Southern Longfin Goby (Favonigobius lateralis), while species with preference for oligohaline/freshwaters i.e. the Western Hardyhead (Leptatherina wallacei) and Swan River Goby (Pseudogobius olorum) dominated the LVRW. Two introduced species, namely the Goldfish (Carassius auratus) and Eastern Gambusia (Gambusia holbrooki), were also captured. The trends in fish composition are then correlated to changes in salinity to demonstrate the effect that the massive fluctuations in this variable have on the fish fauna and show the impact that particular management decisions have on the fish community of the Vasse-Wonnerup.