tracking receivers include the USR-5W and USR-96 manufactured by Sonotronics. These
models measure pulse intervals, a function of depth and temperature, as a means of identifying
non-coded tags. The USR-96 is a narrow band receiver, which improves the detection range and
distinction between tags and is ideal in areas of high background noise. Conversely, their model
USR-90 is a dedicated automatic tracking system, which is suitable for fixed stations, but cannot
be used for manual tracking.
Lotek Wireless first introduced fixed-station datalogging systems in the 1980's. In this
application, one or more receivers are deployed to automatically scan for frequencies in use.
Advances in technology have produced scanning receivers capable of both manual tracking and
automated datalogging combined into a single unit (e.g., SRX-400 manufactured by Lotek
Wireless). During automated tracking, when a valid transmitter is detected, the system records
the time, date, frequency, pulse rate, individual code number (if using coded tags) and signal
strength of the detected fish. A major advantage of scanning/datalogging receivers is continuous
data collection throughout the study period. This technique allows for more data to be collected
than is possible from manual tracking when considering the amount of manpower needed and
associated costs. After initial setup, a single researcher can periodically visit each shore-based
fixed-station monitoring site to download stored data. Depending on the number of tagged fish
being monitored, this may be as seldom as once a week. Data are transferred via an RS-232
serial port to a standard laptop computer. A standard marine battery powers the shore-based
Features to consider when investing in scanning receivers include: the ability to simultaneously
number of individual fishes that can be monitored on a single frequency; detection of coded and
non-coded transmitters; both manual and automated tracking capabilities; the ability to function
within a remote environment in self-contained operation and remote access capability via cellular
phone, radio modem, or satellite.
HIGH RESOLUTION TRACKING: Several telemetry equipment manufacturers produce
systems that are capable of providing real-time, detailed position information of acoustically
tagged fish. Steig (1999) investigated the use of acoustic tags for monitoring juvenile salmon and
steelhead as they migrated downstream in the forebay of the Rocky Reach Dam on the Columbia
River. The tracking system utilized four fixed, wide beam hydrophones with overlapping beams.
Each hydrophone was placed at a known location within a three-dimensional grid. Acoustically
tagged fish passing through the four beams were detected and mapped to sub-meter accuracy by
using the arrival time of each pulse to triangulate the position of each fish. The fish's three-
dimensional movement trajectory was tracked over time. Hydroacoustic Technology
Incorporated (HTI) states that 20 fish could be tracked through the facility simultaneously.
VEMCO's Radio Acoustic and Positioning System (VRAP) employs a similar concept to the
HTI system and is used to measure real-time, high-resolution position information by deploying
a series of detection stations attached to buoys. Buoys are easily deployed from a small boat
and have side and bottom mooring lugs. Each buoy contains a hydrophone, ultrasonic receiver,
two-way radio link, a microprocessor controller, and a rechargeable battery as a power source.
Following initialization, a detected transmitter is positioned based on arrival time of the acoustic