Underwater video techniques have progressed rapidly over the past ten years, and are now used in a diverse range of habitats from small creeks to the ocean depths. A limitation of underwater video cameras is they rely on high levels of water clarity and require artificial lighting if used in low light conditions. In systems such as estuaries, turbidity levels often restrict the use of conventional video. Acoustic cameras (DIDSON) overcome this problem as they rely on sound to produce near video, flowing footage. Our current research is directed in two areas which firstly include the role of light on key ecological functions such predator-prey interactions in estuaries. Artificial light was found to have a strong influence on trophic interactions around anthropogenic structure. A separate study revealed the distribution and behaviour of estuarine predators and prey were related to diel cycles. Larger fish were more active during the day with some moving into shallow habitats at night. This resulted in increased schooling behaviour of baitfish. Secondly, we are using the DIDSON to gain information on the connectivity of estuaries and the coast. Placing the DIDSON at the mouth of estuaries we have been able to enumerate the numbers of fish passing through during tidal phases. We have observed over 4000 fish passing during a single tide, highlighting the potential dynamic nature of estuarine fish populations.