Acoustic tagging is the primary tool used to collect data on white sharks
Acoustic tags emit a series of pulses for up to 10 years, their pattern individually identifying each tag. Some can also transmit information on temperature and swim depth.
Acoustic tags attached to a small arrow-head and a short tether are usually fitted externally to larger sharks (>3 m) using a tag pole as they swim past the vessel.
Many of these tags are placed on sharks at the Neptune Islands for us by shark cage-dive operators.
Juvenile white sharks (< 3 m) are caught and held in a cradle beside the vessel while the acoustic tag is planted in the belly via a minor surgical procedure.
The risk of the tagging procedure (to sharks and humans) is minimised through careful management and observance of health and safety and animal ethics procedures.
Acoustic listening stations
Acoustic pulses from tags are detected and decoded by underwater receivers (listening stations).
Stations record the date and time of each tag’s detection and its sensor data if transmitted.
Sharks need to swim close (typically within 500 metres) to a listening station for its acoustic tag to be detected.
There are two main categories of listening stations that we use:
- conventional units that must be retrieved to access detection data
- real-time units (VR4Gs) that are linked to a surface buoy and can relay the detection of a tagged shark via the iridium satellite or GSM phone network.
Acoustic listening stations are now commonly used by many research agencies in Australia and worldwide.
Australia has a broad-scale coastal network of listening stations maintained by the Commonwealth-funded Integrated Marine Observing System and supported by collaborating agencies.
White sharks tagged in Australia have been detected across their Australian range and in New Zealand.
There are two types of satellite tags commonly used by us that transmit a unique signal and data, if sensors are fitted, via the Argos network of satellite receivers. The signal is used to determine the location of the tag.
The two tag types are satellite tracking tags and pop-off data logging tags.
Satellite tracking tags that are fitted to the dorsal fin and that can send its signal each time fin comes out of the water.
These tags allow scientists to follow sharks over the tag’s battery life.
The accuracy of locations varies depending on how long the shark is at the surface and what satellites are in view: from within hundreds of metres to several kilometres.
Pop-off data-logging tags that are attached by a small tether collect data while attached and that are programmed to release from the shark at a set date and time then float to the surface and transmit their collected data.
These tags allow scientists to reconstruct tracks after the data are received.
Satellite tracking tags are attached to the shark's dorsal fin while the shark is cradled beside the vessel whereas pop-off tags can be darted into a shark as it swims past the vessel without the need to catch it.