Australian fish surveillance

09 Sep 2013
Dr Alistair Becker at Narrabeen Lagoon

Dr Alistair Becker at Narrabeen Lagoon. Credit: UNSW

University of New South Wales researchers are using high-resolution sonar equipment to monitor the fish that swim in and out of Narrabeen Lagoon on Sydney’s northern beaches.

This Australian-first experiment aims to find out how much connection there is between the coastal ecosystem and the fish habitat in the estuary.

The $120,000 instrument is being regularly deployed in shallow water at the mouth of the estuary, which is about 20 metres wide. Known as a DIDSON, it was originally developed for the US Navy for underwater surveillance.

Dr Alistair Becker, of the School of Biological, Earth and Environmental Sciences, says the sonar system can detect all the fish longer than about 10cm that pass by, as well as shoals of smaller fish.

“We can count every fish that swims in and out of the lagoon. And we are seeing a lot of them – with fish moving by every couple of minutes,” he says.

Dr Becker and Mathew Holland, a Master’s student, carry out the research during the night and the day, and are monitoring both in-coming and out-going tides in the channel.

A water-resistant camera is also used to photograph some of the fish, which include bream, flathead, tailor and luderick. These images will be compared with the sonar record to see if it possible to identify the type of fish from just the sonar images.

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