Transmitting Tags

ERDC TN-DOER-E18

February 2005

retrieve the tag to download the stored data. The researcher can attempt recapture, although this

option may require many additional hours of field time and may prove financially infeasible. A

second option would rely on commercial or recreational fishermen to retrieve and return the tag

once the fish has been taken.

The satellite tag is another type of DST tag that does not require recapturing the tagged fish to

access the data. Satellite tags store data until the animal surfaces and then transmit the data to a

remote receiving station. The ARGOS data collection and location system, which has receivers

located on a NOAA orbiting satellite, receives and stores the transmitted data. The system uses

UHF radio frequencies and its Doppler location system depends on a stable transmitter frequency

of 401.640 MHz. For this monitoring technique to be successful, the species studied must

surface with enough regularity to transmit data to the satellite, which is overhead for a limited

number of times daily (up to 15 times at higher latitudes). While this type of tagging operation

has been extensively used to track migratory patterns of sea turtles (Keinath et al. 1989),

applications in fisheries research have been limited to large sharks.

The primary disadvantage of satellite telemetry is that it requires a large initial investment.

Individual satellite tags can range in price from $3,000 to $4,500. This amount per single tag is

approximately 10 to 15 times the amount of a single acoustic or radio transmitter. However,

satellite telemetry may be cost-effective in certain situations. Mech and Barber (2002), Gorman

et al. (1992), and Fancy et al. (1989) compared costs of conventional VHF and satellite telemetry

and found VHF telemetry to be 43 times greater, especially when working with remote species

that are difficult to track or in distant oceans. In addition, costs associated with active tracking

such as personnel salaries and travel/living expenses are avoided. A principal advantage is the

ability to collect several month's to year's worth of data for a single animal. Satellite telemetry

tags allow collection of data that define migratory patterns, vertical movement patterns within

the water column, and water temperature relationships.

Transmitting Tags. This category can be sub-divided based on whether the signal

transmission is either "pulsed" or "coded." For pulsed tags, a simple pulsed signal, a familiar

"beep-beep-beep" is transmitted at a selected pulse rate. Pulsed systems identify tagged fish

through frequency separation combined with a variety of pulse rates. In theory, large numbers of

fish can be tracked simultaneously by using multiple frequencies combined with different pulse

rates. A limiting factor for pulsed tag usage reported in Thorsteinsson (2002) is that many

researchers have difficultly distinguishing more than five pulse rates on a single frequency.

Coded tags operate by emitting a distinct and unique numerical code that differentiates it from all

other tags. Coded tags offer a clear advantage over pulsed tags in that many individual fish

(some manufacturers report monitoring as many as 212 on a single frequency) can be tracked

separately on a single frequency. Those data can be automatically recorded by a datalogger and

downloaded to a laptop computer. Radio, acoustic (sonic), and combined radio/sonic tags

comprise this category. Examples of radio (upper four) and sonic (lower three) tags and their

typical size ranges, manufactured by Lotek Wireless Inc., are found in Figure 1.