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Satellite Tracking and Manatees
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Tie a Belt Around Your Peduncle!

All this talk about "tags" and transmitters may have you wondering. What do the tags look like, how are they attached to the Manatees, what kind of signals are sent out or received, how long do they last, what is a 'tip' and what happens if the tag gets caught in something?

Credit: USGS-Sirenia

Journey North students tracking the migration of the Bald Eagle know that the eagle wears a "backpack" transmitter. Manatee tags, on the other hand, are attached with a "peduncle belt" and a "nylon tether." The belt goes around the manatee just in front of its tail, in an area called its "peduncle", and the tether is a stiff nylon rod (about 10 mm in diameter and 130 to 200 cm long) that connects the belt to the tag. Each tether has a "weak link" built into it, which will break and allow the manatee to swim free if the tether or tag ever become snagged on something such as a dock, a boat, thick vegetation, or even a hungry alligator!!

Credit Birmingham Zoo

Take a look at this video of scientists fitting a captured manatee with an transmitter and the releasing it back into the water:

Watch a Manatee Being Fitted with a Transmitter

click to enlarge

Radio Waves
Jim Reid and Susan Butler from the Sirenia Project explained that most manatee tracking has been accomplished through the use of very high frequency (VHF) and Argos-monitored radio-tags. Both of these systems are usually combined in one tracking tag, and both rely on radio transmitters to broadcast signals from the tagged manatee. The tags are also usually equipped with a third transmitter, which gives off sonic beacons.

Signals from the Argos transmitter are received by NOAA weather satellites and relayed back to earth for processing; researchers then use computers and the Internet to get the calculated locations from Service Argos. To locate a Manatee, scientists will begin with location coordinates from the Argos satellite system, and travel to that area.


VHF Receiver
Click image for a closer look

Once in the field, the next step is for researchers to use the VHF signals to narrow down the location of the manatee. Researchers in boats do this by using antennas and radio receivers tuned to the specific VHF radio frequency assigned to that specific manatee's transmitter. When the VHF signal is very strong, researchers will then narrow their search even more, and turn to listening for the sonic beacons, using a hydrphone which they lower in the water. When they hear the sonic beacons with the hyrdrophone, the scientists will now know the direction the Manatee is located in. At this point using the sonic beacons, the Manatee is usually within 50 to 100 feet away, and the scientists watch for the Manatee's tag in the water.

The radio transmitters are contained inside of floating plastic cylinders about 39 cm long and 9 cm in diameter. The cylinders have a 20 cm wire antenna on the top of them, and every cylinder is color-coded with large identifying letters and engravings on them.

Sirenia Project tracking tag expert Susan Butler holds a completed VHF/PTT tag which she built in the lab
Click image for a closer look

As noted above, each cylinder usually has three different transmitters inside it. One is called a VHF transmitter, which sends specific radio frequency signals to scientists in the field using a portable receiver and antenna. The other is called a Platform Transmitter Terminal or "PTT", and it sends out location signals to an orbiting satellite. The third is the sonic transmitter, which sends a very localized signal which scientists listen for using a hydrophone in the water.

Typically, the PTT will send from two to six different location points for each tagged manatee every day. Besides "location" information, data is also sent on manatee "activity" (# of dives, duration of dive, # of times the transmitter "tips" greater than 90 degrees, i.e. swimming, playing, etc) and temperature.

Disassembled VHF/PTT tag components next to the cylinger which holds them.
Click image for a closer look

According to Cathy Beck, satellite tracking data can be inaccurate or be interrupted for several different reasons. "The quality of the location plotted by the satellite varies, depending on whether the Manatee (actually the antenna) is at the surface when the satellite passes--the antenna must reach the surface in order to broadcast the signal to the satellite. Also, data quality can be affected when there are a lot of structures or vegetation that may interfere with the signal. Finally, transmitters (and regrettably manatees too) can be damaged if struck by boats"

"Beeping" or "Listening":
The Difference Between Radio-Tags and GPS Tags

Jim Reid pointed out that radio tracking and GPS tracking are very different processes. "Unlike the radio tag which sends signals ("beeping"), the GPS tag attached to the Manatee is a radio receiver ("listening") that is tuned to signals being transmitted from NAVSTAR satellites. The GPS receiver then calculates a location and stores it to memory in the tag. These locations are normally very accurate and the tag can be programmed to obtain many locations per day. Unfortunately, the GPS tag must be recovered for us to download the stored locations and plot where the manatee has been. New technology is being developed to relay the stored GPS data to researchers, perhaps through an Argos-monitored transmitter!"

For more details on GPS Technology go to:

Special thanks to Service Argos for their ongoing assistance.

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