The small, low wattage PTTs attached to the turtles are controlled by a micro-processor which is programmed by a computer before it is attached. The program tells the microprocessor how to store information and when to transmit the information to the satellites. The data received from the turtle’s transmitter comes in the form of digital codes, which must be deciphered. The satellites relay the transmitter data to base stations on Earth. The base stations then relays the data directly to researchers by e-mail.
Polar orbiting satellites are currently used for tracking animals. The satellites are operated by the U.S. National Oceanic and Atmospheric Organization (NOAA) and are the same satellites used to monitor global weather patterns. Attached to these satellites are special instruments operated by a French company, ARGOS CLS. These special instruments are designed to listen for transmitters like those we place on turtles and to determine where those transmitters are located. While such a task would seem simple, it is not. Each satellite circles the earth every 101 minutes and so it is only over any one place on the planet for about 10 minutes. At the equator, this means that the satellites make about 6-8 passes per day for 10 minutes each. For the satellite to determine the location of the transmitter it takes about 3-5 minutes, and the transmitter must be on the surface to be detected. Location error can vary between 50 m and 2.5 km depending on the number of satellites overhead, how long the satellite can detect the transmitter, and the number of messages received from the transmitter. However, turtles rarely remain on the surface for that long, and their surfacing must coincide with multiple satellites passing overhead. Thus, the quality and number of locations received for a turtle can vary greatly from day to day.
Using computer mapping programs, researchers can plot the spatial movements of the turtle, the route they have traveled, where they go to find food, and estimate how fast they are generally swimming. Depending on the detail of the map being used, a researcher can also determine the habitat characteristics at the turtle’s location. The data received from the turtle’s transmitter comes in the form of digital codes, which must be deciphered. The codes allow researchers to determine, with varying degrees of reliability, the latitude and longitude location of the turtle, the number of dives taken during the last 24 hours, the duration of the most recent dive, and the water temperature, among other information.
While viewing the migration maps shown on this site, viewers should be aware that the plotted turtle movements represent the best data available; however, any given location mark may not be 100% accurate. This limitation really doesn’t detract from the overall value of the research. While a particular location point may actually be miles off a given turtle’s actual location, the accumulation of data stills tells us where the turtles are generally moving and where their primary foraging areas are located. Using this information, we can begin to focus conservation efforts where they are most needed.
