We have not received any data from Katia in a few days now. One possible reason for the lack of data may be that she is simply moving too fast. Katia is being tracked with a towed transmitter that is attached via short tether to her peduncle (rear end of her carapace) and this transmitter only breaks the surface as the turtle rests at the surface or is moving slowly.
Receiving data from a sea turtle in the ocean is a rare occurrence. Three things must occur:
- The transmitter must be on.
Tracking devices are designed to relay data as programmed with a duty cycle to conserve battery life. (you cant change batteries in the ocean…) Katia’s tag is programmed to relay data every other day for a period of twelve hours. - The turtle must be at the surface.
Radio waves do not transmit through water, so tags are designed with a simple device to determine when the turtle is at the surface. When that occurs, IF the transmitter is programmed to transmit, it will send a burst of data up into the sky. - The must be a satellite overhead. (Now this is the important part!)
The satellite system employed by most wildlife tracking biologists is called the Argos system. This system currently consists of seven weather satellites orbiting the earth which contain an Argos receiver that is tuned to a specific frequency listening to lots of different transmitters. At the latitude where Katia is currently located we can expect about 240 minutes of time when a satellite is in the range of her transmitter. A satellite pass will average about nine minutes per pass, with only a few minutes where the satellite is high enough overhead for the transmitter to reach. As seas get rougher, the chances of successful data transmission become much lower.
On a typical day, we will only receive 8 packets of data from a typical migrating leatherback. So, we are not too worried about the lack of data at this point.
The next post will explain more about the transmitter she is towing and further options for lack of data. Stay tuned…