Estuaries are places of transition from freshwater to seawater. They occur at the end of rivers and are subject to marine and freshwater influences. The coastline of Victoria contains approximately 123 bays, inlets and estuaries, varying in water area from approximately 1 to 2000 square kilometres. Estuaries contain diverse ecosystems that support a vast array of Victoria's biodiversity, including specialist plants, fish and invertebrates. As with other environments, estuaries are not without pressures. Issues affecting estuaries include, water quality degradation from increased nutrients, pesticides and heavy metals, reduced freshwater flows due to river regulation and unsustainable use of estuarine resources.

Key projects (with details below):

Development of Methodology for Fish Assessments to Support the Victorian Index of Estuarine Condition Linking Salt Wedge Dynamics of Estuaries to Fish Productivity - Gippsland Lakes Shorebirds and Benthos at the Western Treatment Plant

Distribution of the Threatened Pale Mangrove Goby (Threatened Species and Communities)

Development of Methodology for Fish Assessments to Support the Victorian Index of Estuarine Condition Fish are typically positioned towards the top of estuarine food-webs and will be influenced by a range of physical and environmental properties of estuaries including water quality and habitat availability. There is currently no standard method for assessing fish assemblages in Victorian estuaries. The development of robust methodologies to describe the nature of estuarine fish assemblages will link to the development of ecosystem based condition assessments. These assessments are aimed at monitoring the effects of land use and climate change. Deakin University, in conjunction with DSE, is developing an Index of Estuary Condition (IEC). This will provide a robust method to evaluate the environmental condition, or health, of Victorian estuaries, which will inform their management. The Index measures aspects of particular features that contribute to the overall health of an estuary, including: physical form, hydrology, water quality, sediment, flora and fauna, including fish and birds. The IEC will complement the existing Index of Stream Condition and Index of Wetland Condition to provide a consistent statewide assessment of Victoria’s natural aquatic systems. Scientists at ARI will be trialling different techniques to sample fish populations at estuaries of Port Phillip Bay and Western Port. Fish surveys will be used to assess the composition of fish species assemblages along the salinity gradients of eleven estuaries. Analysis of the isotopic ratios of carbon and nitrogen in fish and plant tissues will also provide information on the structure of food webs and the sources of nutrition for key fish species within each estuary. Aspects of water quality and depth profile are also being recorded to help relate variation in fish assemblages to estuarine condition. Sampling will occur in autumn and spring 2010 to ensure fish species associated with different riverine flow regimes are sampled. Data obtained from this project will ultimately contribute to management tools, including the IEC. Funding is from Melbourne Water, which has responsibilities for achieving healthy waterways in the Port Phillip and Westernport region. For more information contact: paul.reich@dse.vic.gov.au Page Top
Linking Salt Wedge Dynamics of Estuaries to Fish Productivity - Gippsland Lakes The freshwater needs of Australia’s estuaries are poorly understood. How freshwater flows through an estuarine system influences the productivity and dispersion of salt wedges, which are important nurseries for fish larvae. Salt wedges occur at the freshwater-saltwater interface where freshwater flows as a layer over the saltwater ‘wedge’. Maintaining and managing the health of Victoria’s estuaries depends partly on understanding their freshwater requirements and being able to make informed decisions on the allocation of water to them. This study aims to contribute to this understanding, by investigating salt wedge dynamics in the Gippsland Lakes, Victoria. Results from this study will have applications in managing the delivery of freshwater to support fish production within estuaries across Victoria. Information collected on the early life history of fish will be integrated with hydrological modelling to determine links among freshwater flows, salt wedge dynamics and fish production. Field sampling began just after substantial natural flooding of the Lakes in June 2007 and focussed on sampling fish eggs and larvae around salt wedges. ‘Hot spots’ for fish eggs and larvae were found in the vicinity of the salt wedge within the Mitchell, Tambo and Nicholson Rivers, with most bream larvae and eggs found immediately downstream of the salt wedge. To better describe the dynamics of this salt wedge, and improve the ability to model changes in the salt wedge from freshwater flows, the bathymetry of the these rivers is now being mapped. Aspects of water quality such as salinity, temperature and water level are also being recorded. During the current spawning season (September to December 2008) eggs and larvae will be sampled at different depths within the water column and acoustic telemetry will be used to study the movements of spawning fish. This information will provide further information on where, and at what depth, spawning is occurring. This study is being funded through an Australian Research Council Linkage Grant, and is being run in partnership with the Department of Primary Industries, University of Melbourne, Gippsland Coastal Board, West Gippsland Catchment Management Authority, and the Nicholson Angling Club. For more information contact: jeremy.s.hindell@dse.vic.gov.au Page Top
Shorebirds and Benthos at the Western Treatment Plant The Western Treatment Plant (WTP) is managed by Melbourne Water to treat over half of Melbourne’s sewage. The area is also an important habitat for shorebirds, with some species migrating each year to Australia from Arctic breeding grounds up to 12,000 km away. These extraordinary migrations are fuelled by large amounts of food; birds need to build up enormous fat reserves to migrate successfully. Shorebirds are also known as “waders” because they forage by wading in mud and shallow water. They are attracted to the WTP because it provides rich foraging habitat, with very high densities of burrowing invertebrates (“benthos”) found in tidal flats along the foreshore. It is likely that decades of effluent discharges from the WTP have enriched this habitat. Some shorebirds also feed in the shallower freshwater ponds of the WTP. Melbourne Water has commissioned ARI to undertake research to help conserve the shorebirds and their habitat. Protecting or enhancing shorebird habitats is challenging, as the tidal flats and freshwater wetlands in which they live are complex, dynamic habitats. An ongoing study is investigating the relationship between the abundance of shorebirds and their food source at the WTP. Repeated shorebird surveys were coupled with surveys of abundance of their benthic prey. These studies showed that shorebird abundance in the WTP is strongly correlated with abundance of benthos. Benthos abundance was found to fluctuate locally over time, and shorebirds moved their feeding grounds in response. Many questions still need to be answered. For example, why does abundance of benthos vary so much over time? What prey densities are needed to make a foraging site suitable for shorebirds? With a more complete understanding of the relationships between shorebirds and their prey, we will be better placed to ensure that their habitats are managed appropriately. For more information contact: danny.rogers@dse.vic.gov.au The following report is available: ARI Technical Report 169 - Relationships between shorebird and benthos at the Western Treatment Plant [PDF File - 1.3 MB]