Acoustic tags are small sound-emitting devices that allow the detection and/or remote tracking of fish in three dimensions for fisheries research. Acoustic telemetry are commonly used to monitor the behavior of fish, studies can be conducted in lakes, rivers, tributaries, estuaries or at sea. Acoustic tag tracking technology allows researchers to view 3D fish tracks in real-time with sub-meter resolution, Acoustic tags come in an assortment of sizes and weights. To-date, the smallest acoustic tag successfully employed to provide fish behavior data in three dimensions was approximately 0.65 grams, Tag size increases significantly when tracking larger fish for longer periods of time. By tying the received acoustic signature to the type of programmed signal code. The transmitted signal can propagate up to 1 km, each ping comes at a predetermined interval. The signals are encoded for strength to improve range and resolution, thus, an array of receivers allows the user to record the movement of a particular fish over many kilometers. Unique to Acoustic Tags is the capability to have over 100,000 user-specified individual tag ID codes with battery lives up to four years and these variables allows a custom fit for unique projects. By determining the time of arrival at each hydrophone, the 3D position of the fish can be calculated. The hydrophone receiver picks up the signal and converts it to data that researchers use to plot the resulting tag positions in three dimensions, in real-time. Using a post processing software, such as MarkTags, takes that data and delivers the end result, Acoustic tags can be attached to, gastrically inserted in or surgically implanted into fish. Several different types of methods are used to attach the tag to the fish, the tag may be embedded in the fish by cutting a small incision in the abdominal cavity of the fish, or put down the gullet to embed the Acoustic Tag in the stomach. External attachment using adhesive compounds is not used for fish as scale fluids do not allow for any successful attachment to scale tissue. Acoustic Tags are produced in different shapes and sizes depending on the type of species being studied. Sound parameters such as frequency and modulation method are chosen for optimal detectability, for oceanic environments, frequencies less than 100 kHz range are often used, while frequencies of several hundreds of kilohertz are more common in for studies in rivers and lakes. A typical Acoustic Tag consists of a transducer, drive/timing electronics. Cylindrical or “tube” transducers are used, which have metalization on the inner and outer walls of the structure. In normal operation, an alternating current electrical signal generated by the electronics is impressed across the two metalization layers
Example of post surgical implantation of tag.
Examples of acoustic tag sizes
Illustration of juvenile salmonid travelling through a fish by-pass intake.
Acoustic tag tracking software screen of fish travelling toward a fish bypass intake (side view).