Fish living in a certain lagoon near Sydney are ready for their high-definition close-up, with UNSW teams monitoring entrants to the Narrabeen Lagoon in an Australian-first project.

Researchers from the University of New South Wales’ School of Biological, Earth and Environmental Sciences have been using a fancy piece of high-resolution sonar equipment at the mouth of the estuary, watching all fish over a few centimetres in length as they pass the 20 metre wide inlet.

Dr Alistair Becker says wielding the $120,000 scanner gives them a better count than ever before: “We want to find out how much connection there is between the coastal ecosystem and the fish habitat in the estuary. This is the first time this has been done anywhere in Australia... 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.”

A traditional water-resistant camera has also been used to take sample photographs of the fish. The team hopes to compare visual records with sonar read-outs to develop a way of identifying fish based on their sonic profile.

The sonar device was originally developed for the US Navy. Similar counts have been conducted to estimate the amount of fish larva entering estuaries intermittently open to seawater, such as Sydney’s Narrabeen Lagoon, “but no-one has looked at the movement of larger fish on a daily basis in and out of the estuary,” Dr Becker says.

The study seems to have attracted some monitoring of its own: “The fieldwork is being conducted in a very public place and, as you might imagine, has generated quite a lot of interest from people walking past,” Dr Becker added.