- Acoustic tags
Acoustic tags are small sound-emitting devices that allow the detection and/or remote tracking of fish in three dimensions. Commonly used to monitor the behavior of fish, studies are conducted in
lakes, rivers, tributaries, estuariesand at sea. Acoustic tag tracking technology allows researchersto view 3D fish tracks in real-time with sub-meter resolution.
Examples of Acoustic Tag Sizes
Acoustic Tag Overview
Acoustic Tags transmit a
soundsignal or "ping" that sends location information about the tagged fish to the hydrophonereceiver. By tying the received acoustic signature to the known type of programmed signal code, a specific fish is identified. The transmitted signal can propagate up to 1 km (in freshwater). Each "ping" comes at a predetermined interval. The signalsare 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. These variables allows a custom fit for unique projects.
By determining the sound's time of arrival at each hydrophone, the 3D position of the fish can be calculated. The hydrophone receiver picks up the sound signal and converts it to
datathat researchers use to plot the resulting tag positions in three dimensions, in real-time. Using a postprocessing software, such as "MarkTags", takes that data and delivers the end result, the 3D track.
Illustration of juvenile salmonid traveling through a fish by-pass intake.
Acoustic tags can be attached to, gastrically inserted in or surgically implanted into fish (or almost any aquatic life).
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 (surgical implantation), or put down the gullet to embed the Acoustic Tag in the stomach (gastric implantation). External attachment using adhesive compounds is typically not used for fish as scale fluids do not allow for any successful attachment to scale tissue.
Example of post surgical implantation of tag.
Acoustic Tags are produced in many different shapes and sizes depending on the type of species being studied, or the type of environment in which the study is conducted. Sound parameters such as
frequencyand modulation method are chosen for optimal detectability, and signal level. For oceanic environments, frequenciesless than 100 kHz range are often used, while frequencies of several hundreds of kilohertzare more common in for studies in rivers and lakes.
Acoustic tag tracking software screen of fish traveling toward a fish bypass intake (side view).
A typical Acoustic Tag consists of a piezoceramic
transducer, drive/timing electronics, and a battery power source. Cylindrical or “tube” transducers are often used, which have metalization on the inner and outer walls of the structure. In normal operation, an alternating current (AC) electrical signal generated by the drive/timing electronics is impressed across the two metalization layers. This voltage creates stress in the material, which in turn cause the transducer to emit an acoustic signal or “ping”, which emanates outward from the surface of the tube. An acoustic “ping” can be detected by specialized receivers, and processed using advanced signal processing techniques to determine if a fish swimming into the reception area carries a specific acoustic tag.
Acoustic Tags are distinguished from other types of devices such as radio tags, or passive inductive transponder (PIT) tags, in that they can work in either salt or freshwater (RF and PIT tags perform poorly in saltwater) and do not depend on steering the fish in a particular path (PIT tags require the fish to be routed through a restricted sensing area).
Current Application Examples
At present, acoustic tags are most commonly used to monitor fish approaching diversion and guidance structures at hydropower dams. This allows hydropowered dam facilities, public utility districts, and municipalities to evaluate specific migration pathways used by the fish (most often salmon smolts), identify where fish mortality occurs and assess fish behavior in relation to hydrodynamic conditions and/or any other environmental parameters. Ultimately, working to improve bypass effectiveness and protect fish populations, Acoustic Tag Tracking Systems are a significant breakthrough in the preservation of migrating salmon populations. For an example of Acoustic Tag Tracking Systems at work on the
Columbia River, see [http://www.gcpud.org/stewardship.htm Grant County's] most recent [http://www.gcpud.org/hydro/bypass.htm application] or [http://www.chelanpud.org/ Chelan County's] most recent [http://www.chelanpud.org/tools-to-help-fish.html application] .
Biologists, engineers, and clients have authored thousands of technical reports and publications on fisheries acoustics. The following is a small sample of journal publications and technical reports available.
Improved techniques for studying the temporal and spatial behavior of fish in a fixed location. Ehrenberg, J.E. and T.W. Steig. 2003. ICES J. Mar. Sci. 60:700-706.
A method for estimating the "position accuracy" of fish tags.Ehrenberg, J.E. and T.W. Steig. 2001. ICES J. Mar. Sci.
Monitoring the three-dimensional behavior of acoustically tagged salmon approaching hydropower dams in the Pacific Northwest. Steig, T.W., M.A. Timko, P.A. Nealson. 2002. Presented at the 6th ICES Symposium on Acoustics in Fisheries and Aquatic Ecology, Montpellier, France.
Monitoring the behavior of acoustically tagged chinook and steelhead smolts approaching Rocky Reach Dam on the Columbia River. Steig, T.W., B.H. Ransom, and M.A. Timko. 2001. Presented at Waterpower XII, July 9-11, 2001, Salt Lake City, Utah, USA.
The use of acoustics tags to monitor the movement of juvenile salmonids approaching a dam on the Columbia River. Steig, T.W. 1999. Presented at the 15th International Symposium on Biotelemetry, Juneau, Alaska, USA, 9-14 May 1999.
Summary of the use of hydroacoustics for quantifying the escapement of adult salmonids (Oncorhynchus and Salmon spp.) in rivers.Ransom, B.H., S.V. Johnston, and T.W. Steig. 1998. Presented at International Symposium and Workshop on Management and Ecology of River Fisheries, University of Hull, England, 30 March-3 April 1998.
Acoustic monitoring of salmonid density, target strength, and trajectories at two dams on the Columbia River, using a split-beam scanning system.Steig, T.W. and T.K. Iverson. 1998. Fisheries Research 35, 43-53
[http://www.chelanpud.org/rr_relicense/existing/hcp/Studies/fish_studies.htm Additional Publications]
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