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Tagging and Tracking Technologies for Freshwater and Marine Fishes
Transmitting Tags
February 2005
tag size to less than 2 percent of total body weight. Typically, researchers use the largest tag
appropriate for the species under study. From this constraint, the range of detection and the tag
operational life are determined.
Electronic tags can be divided into three basic categories to include transponding, data storage or
archival, and transmitting. Although the focus of this technical note is tagging and tracking of
aquatic and marine fishes, each category will be discussed briefly along with a prominent
tagging option.
Transponding Tags. The Passive Integrated Transponding (PIT) tag is an inert, small glass-
encapsulated electromagnetic coil and microchip that is inserted into the body cavity or muscle
mass of a fish using a veterinary syringe. Tags are activated and the emitted signal read by a
device held approximately 10-15 cm from the tagged animal. The signal is a unique alpha-
numeric code (signal strength 40-50 kHz) for each tagged fish. Automatic readers are also
available with either a tunnel detector (up to 30-cm diameter) or a strip detector, which can be
placed on the streambed (up to 20-cm water depth). Pit tags generally range from 11 to 28 mm in
length and 2.1 to 3.5 mm in diameter. Two systems are currently marketed (Trovan and
Destron); however, they are not compatible, i.e. their respective reader devices will not detect the
other's signal. Web site addresses are provided for each manufacturer at the end of this technical
Two example studies using PIT tags include measuring the migration of wild Snake River
Chinook salmon smolts (Achord et al. 1998) and designing a tag system for monitoring
American shad and blueback herring in fishways (Castro-Santos et al. 1996). The tags were
implanted in the juvenile fish at the beginning of their migration. Each tag is unique and
identifies one particular fish. Detectors located at dams can read the tags on the out-migration
and when the fish return as adults to spawn.
Advantages of PIT tag usage include detection in both aquatic and marine environments, and the
availability of billions of unique codes (Prentice et al. 1990). PIT tags are also economical,
costing approximately $6 per tag, as compared to transmitting tags that cost hundreds of dollars
each. A PIT tag requires no power source and the tag remains inactive inside the fish for its
lifetime, until activated at a PIT-tag monitoring station or by a hand-held reader. The limiting
usage factor for many studies is a very short detection range of 20 cm.
Data Storage Tags (DST) or Archival Tags. Data storage tags, also known as archival
tags, may function simply as data loggers that measure temperature and water depth, for
example, or as sophisticated programmable devices capable of recording direct estimates of the
geographical position of a fish at regular intervals over periods of months to years (Thorsteinsson
2002). DSTs are also capable of recording temperature, depth, salinity, pressure, light and
chemical and physiological indicators at set intervals. They have been used in open-water
environments with free ranging fish such as tuna, Pacific and Atlantic salmon, sea trout and cod,
among others. Advantages include the ability to collect data for up to five years and to store this
information within the tag for up to twenty years. This allows a vast amount of data to be
collected by a solitary tagging event. There are two primary disadvantages with DST tags. These
include the high cost associated with the tags as well as the necessity to recapture the animal to

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