Summary

The DIDSON is a digital acoustic camera system developed by the Applied Physics Laboratory at the University of Washington, USA. It uses an array of sonar beams to provide digital images of objects in waters with little or no visible light transmission. Trials were carried out to determine the effectiveness of the DIDSON for assessing fish passage through tidally activated floodgates on the entrance channel to the Little Broadwater wetland in the Clarence River, NSW, Australia. A trap net was used to verify the identification of fish passing through the floodgates. Trials were also carried out in riverine habitats in the Clarence and Hunter Rivers to determine the effectiveness of the DIDSON for surveying fish in riverine habitats, where DIDSON observations were compared with electrofisher samples. These trials showed that the DIDSON is a very useful tool for assessing quantitative and behavioural aspects of fish passage and habitat usage in a range of habitats. Some potential applications of the DIDSON for assessing fish habitat usage in riverine and coastal wetland habitats are discussed.