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Acoustic tags are electronic tags that transmit information on a particular frequency. This frequency is outside the range of the animals hearing so it does not disturb them.
Acoustic tags transmit a unique code that can be detected by listening stations set on the bottom of the ocean, (these stations record the date and time a tagged animal is present in the area), or can be used to follow an animal from a small boat. Sensors on acoustic tags can also transmit data including swimming depth, swim speed and water temperature.
Code-swapping the key to acoustic network
The use of acoustic ID tags to trace the movements of marine animals such as sharks, rays, finfish, and mammals has risen rapidly in the past few years and the data they gather are being exchanged by Australian and international scientists.
Acoustic ID tags transmit a unique code at regular intervals which, when in range, is logged by an electronic receiver or ‘listening station’ on the seabed, or a hydrophone operated from a vessel. Animals carrying tags can be detected when in the vicinity of any such listening station, anywhere in the world.
For example, white sharks tagged off South Australia by CSIRO have been detected by acoustic listening stations established primarily to detect tuna off south-west WA, and grey nurse sharks off the mid-north coast of NSW.
A network of listening stations is gradually being established around the southern, eastern and western coasts of Australia, maintained by various research groups. The effectiveness of this network will depend on the exchange of data between researchers and by the common listing of their assigned tag codes.
There is also the possibility of highly migratory species such as sharks and tuna being detected by listening stations deployed in other countries such as New Zealand, Indonesia, - South Africa and the US.
What is acoustic tagging?
Acoustic ID tags can be attached externally or internally. As well as transmitting a unique, identifying code, they can be fitted with sensors that transmit a variety of data including water temperature, swim depth and swim speed.
Acoustic ID tags are commonly used to record the extent to which an animal uses a particular area, and how this behaviour may change over time. They are suited to research on any species to which a transmitter can be attached or implanted without modifying its behaviour, such as fish, sharks, crustaceans and squid.
Acoustic receivers, or ‘listening stations’, can record the presence of thousands of animals fitted with acoustic ID tags. Tagged animals can be recorded visiting a monitored site, such as the Neptune Islands in SA, or can be tracked over hundreds or thousands of kilometres by placing multiple receivers in grids or lines. Tag-to-tag data transfer is likely in future.
CSIRO has fitted acoustic ID tags to more than 30 white sharks (tagged off South Australia) and plans to continue tagging as opportunities arise and has plans to tag some 50 more in the next few years. Listening stations are permanently set at the Neptune Islands.
Satellite tracking, and acoustic tagging in South Australia, along with tracking and sighting data, suggest that white sharks from this region move extensively throughout Australian waters. Specific sites may be revisited on a seasonal or more sporadic basis by some sharks, but no sharks permanently reside in a particular area.
Last updated 12/11/08