The significance of water flows for estuaries, Riversymposium Conference, Brisbane 2009

Estuaries are the most downstream point of a river and are the conduit between fresh and saltwater ecosystems and by definition, have a gradient of fresh to saltwater. Estuaries are dynamic places, with many parameters constantly changing. The main role of water flows to estuaries is initiating change in estuarine parameters e.g. salinity, flow rate, turbidity, wetted area, nutrient load. In northern Australia, wet season rains bring substantial freshwater flows, inundating large areas of the estuary. Flooding and associated nutrient and sediment delivery is an essential part of the seasonal stimulus to estuarine biological productivity. Fish catch and other measures of production can be used as an integrated measure of the significance of water flows to estuaries. Often, fisheries production is the only long-term measure of the benefit of flows to estuaries; can also reflect the environmental state of the estuary; and has high community and indigenous value. We used a logical decision making framework to investigate the links between estuarine fisheries production and freshwater flow in tropical Australian estuaries. Multiple measures of estuarine fisheries production were investigated. Decadal catch data, yearly recruitment indices, monthly growth rates and short term fish movement were all significantly and positively influenced by freshwater flows to estuaries. Freshwater flows bring long and short term benefits to estuaries. The development potential of tropical Australian rivers needs to be considered against the potential downstream impacts on estuarine ecology, of which fisheries production is one measure.