The other morning I was walking the dog and went to the headland at the northern end Stanwell Park to look for whales and a relatively large boat motored in from the north and proceeded to install a shark listening station, which has generated quite a bit of discussion amongst the locals.
As the photograph shows the listening station has a float on the surface which sticks up about 2 metres. Ours is number 35 and is about 900 metres or so off the beach. There are at least 22 of these along the NSW coast and the government plans on a total of 37.
The listening stations are so called because they are designed to pick up ‘pings’ from sharks that have been tagged with an acoustic tag – largely great whites, tigers and bulls. This is inserted into the shark after it has been caught (commonly on a drumline – a baited hook attached to a float on the surface) via an incision (followed by a few stitches!). The battery can power the tag for anything up to 10 years.
The ping from the tag can be detected out to about 500m. So, when the shark is in range of the listening station the data from its individual tag can be read. If the shark passes multiple listening stations over time then a picture of its movements can be built up. There is an analysis of several years of data on the Shark Smart area of the NSW Department of Primary Industries website.
The ping from the shark gets transmitted to a shore station and then to the Shark Smart app (and Twitter) so if there is a shark within 500m of the listening station you can get to know about it. The main purpose of the listening stations is research, not bather protection, as most sharks are not tagged. For example, about 400 great whites have been tagged out of an estimated 3000.
Listening stations are also used for a lot of other fisheries research. A colleague used them to monitor movements of flathead in Jervis Bay. Other types of tags are also used for fish research, including satellite tags which can be attached to the dorsal fin of sharks and transmit when the shark is on the surface.
