Acoustic tags, which can last for up to 10 years, emit a series of pings over a short period of time that provide a unique identification for each tag — some of the tags can also transmit information on temperature and swim depth.
Our acoustic tags are surgically implanted to enable more data to be collected over the lifespan of the tag.
For our tagging, 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 animal ethics procedures and health and safety.
Acoustic listening stations
Acoustic pulses from tags are detected and decoded by underwater receivers (listening stations).
Listening 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 are used in Australia:
- 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.
This animated sequence shows a white shark swimming with acoustic pulses from its acoustic tag detected by underwater receivers (listening stations).
There are two types of satellite tags commonly used 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 are fitted to the dorsal fin and can send a signal each time the fin comes out of the water.
These tags allow scientists to follow sharks over the tag's battery life.
The accuracy of locations varies from within hundreds of metres to several kilometres depending on how long the shark is at the surface and how many satellites are in view.
Pop-off data-logging tags are attached externally by a small tether. These tags collect data while attached and are programmed to release from the shark at a set date and time then float to the surface and transmit their collected data to the researchers via the satellite network.
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.
Tagging and animal ethics
Our tagging protocols adhere to strict animal ethics and state regulations and approval is needed to interact with, and tag, white sharks.
The anchoring of satellite tags on white sharks is a swift process Our research has demonstrated that during application of the tag white sharks show no signs of distress. There is no scientific evidence that tagging causes any short- or long-term harm to the shark or changes in behaviour.