Advances in Radio Tag Technology

ERDC TN-DOER-E18

February 2005

telemetry would not be the best-applied technology due to degraded signal transmission through

the water column. Radio telemetry is especially effective for highly mobile fish in shallow rivers

(migrating anadromous species) because aircraft surveys can often locate fish dispersed over

hundreds of miles, which may be outside the normal survey range of most field crews if

monitoring is conducted from a small boat.

For fishes occupying surface waters, radio tags can be detected to a distance of 1 to 3 km, when

using a boat-mounted antenna. This distance is increased by several additional kilometers when

antennae are mounted on aircraft. When using a land-based fixed monitoring station, site

selection is extremely important since signal strength can be degraded by upland vegetation,

buildings, and industrial facilities.

The operational life of radio tags has improved substantially in recent years. Two factors that

most influence tag life include: battery size and the rate of signal transmission. The researcher

can select optimal pulse rates based on size of the study population, duration of the study, and

the mode of tracking. One manufacturer, for example, offered tags with pulse rates ranging from

30 to 240 bpm. However, increases in pulse rate mean decreases in tag life. For example, a

pulsed radio tag (dia x L = 7.3 x 18 mm, weight 0.8 g) with a pulse rate of 30 bpm would last 12

days; however, if increased to 60 bpm, tag life would decrease to 7 days. Most vendors offer tags

ranging in weight (in water) from 2.0 to 45 grams. Tag life varied, depending on transmission

rates from as little as 7 days for the smallest tags to 3.2 years for the largest. Radio tags can be

configured with delayed start times, and definable hourly, daily, or weekly activation periods,

which can conserve battery life.

Advances in Radio Tag Technology. Continued advancement in radio transmitter

technology has produced transmitters of ever-decreasing size and weight. Several companies

offer a series of miniature tags. "MiniFish Tags" (AVM Instrument Company), the "NanoTag

Series" (Lotek Wireless), and the "Itty-Bitty" miniature transmitters (Sonotronics) offer radio

tags designed to track salmon smolt or other migratory species of similar sizes.

The standard AVM minifish tag consists of an SM1 radio transmitter, battery, tuned loop

antennae, and magnetically controlled on/off switch. The overall design is roughly padlock

shaped, with the loop of the antennas analogous to the shank of a padlock. Tags come in five

models with an operational life ranging from 4 to 90 days. Weight in water averages less

than 3 grams for the largest tag. Dimensions are generally 8 mm in thickness, 9 mm total width,

and from 17 to 29 mm in length. These tags are also available for larger fish with battery life

ranging from 3 months to 2.5 years. Weights for these tags range from 5 to 26 grams.

The "Itty-Bitty" miniature transmitter series manufactured by Sonotronics offers three tag

models ranging in weight in water from 1.5 to 3.2 g. Length and diameter range from 25 to 36 mm,

and 8 to 13 mm, respectively. Expected tag life ranges from 21 days to 5 months. Detection

range is reported to be 500m+. Average costs were $250 per transmitter.

The NanoTag Series produced by Lotek Wireless is the smallest digitally encoded transmitter

currently available. Using micro-circuitry design, the tags incorporate three distinct technologies;

radio, digital processing, and infrared on an Application Specific Integrated Circuit. This yields a