Transponding Tags

ERDC TN-DOER-E18

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

note.

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