Abstract
Estuaries are widely regarded as the most degraded of all aquatic ecosystems, largely due to their exposure to a range of deleterious anthropogenic influences. In the case of the Vasse-Wonnerup, such impacts have included, land clearing for agriculture and associated severe eutrophication, the diversion of river flow and the construction of barriers (floodgates) to prevent the intrusion of saltwater into the estuary. Although the prevention of flooding and maintenance of surrounding pastoral land has been achieved, the Vasse-Wonnerup now suffers from regular fish kills and algal blooms. Current managers are thus faced with the problem of managing the legacy of historical decisions, while also being under community and political pressure to introduce additional (but noncompromising) measures to reduce the frequency and severity of deleterious events. This poster details the anthropogenic changes that have occurred in the Vasse-Wonnerup over the last 120 years and describe the resultant changes in environmental conditions and how these influence the fish community. For example, fish faunal composition undergoes marked seasonal and regional changes in response to changes in dramatic changes in water quality and there is the seasonal expatriation of fish from particular regions of the estuary at times during the year. Moreover, growth rates and condition of the key recreational species Black Bream Acanthopagrus butcheri are poor in comparison to nearby systems. Ways to ensure the maintenance of a viable fish population in this estuary are discussed.