An acoustic tag is a small sound-emitting device that allows the detection and/or remote tracking of fish in three dimensions

Three-dimensional space

Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...

. Acoustic tags are commonly used to monitor the behavior of fish. Studies can be conducted in lakes, rivers, tributaries, estuaries or at sea

Sea

A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...

. Acoustic tag tracking technology allows researchers to view 3D fish tracks in real-time with sub-meter resolution. Acoustic tags have been employed to help public utility agencies, private firms, and state and federal agencies meet fisheries regulations as defined by the Federal Regulations and Oversight of Energy known as FERC.

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 (tracking a juvenile salmonid at a length of 125 mm). Tag size increases significantly when tracking larger fish for longer periods of time (i.e. sturgeon).

Overview

Acoustic tags allow researchers to:

• Conduct Fish Survival Studies
• Monitor Fish Migration/Passage/Trajectory
• Track Fish Behavior in Two or Three Dimensions (2D or 3D)
• Measure Bypass Effectiveness at Dams and other Passages
• Observe Predator/Prey Dynamics and More

Acoustic Tags transmit a sound

Sound

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

 signal or "ping" that sends location information about the tagged fish to the hydrophone

Hydrophone

A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...

 receiver. By tying the received acoustic

Acoustics

Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

 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 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. 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 data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 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, the 3D track.

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.

Details

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 frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 and modulation method are chosen for optimal detectability, and signal level. 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 piezoceramic transducer

Transducer

A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...

, 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).

Applications

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

Fish mortality

Fish mortality is a term widely used in fisheries science that denotes the loss of fish from a stock through death. The term is also commonly used in British English as a synonym for fish kill. Fish mortality can be divided into two types:...

 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

Columbia River

The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

, see Grant County's most recent application or Chelan County's most recent application.