Under certain conditions the Center, one of the disentanglement network members, or one of its first responders may be on site of an entangled whale, but be unable to initiate or complete the disentanglement of the animal. Under these circumstances the disentanglement network may use telemetry, the use of transmitters to remotely obtain data, and monitor the whereabouts of the animal until the rescue can be completed. Telemetry on whales was pioneered in the 1960s by William E. Schevill and William A. Watkins (1962). Since then VHF and more recently satellite transmitters have been used on a variety of whales to understand their movements, distributions, and activity patterns.
VHF radio transmitters, or tags, transmit Very High Frequency radio signals which can be picked up by a receiver in real time. However, they are limited in range to line-of-sight. Depending upon the height of both the transmitting and receiving antennas, and the power of the transmitter, a vessel tracking a tagged whale may only pick up the animal from several miles away. On the other hand, satellite tags have a more broad range since circumpolar satellites relay the position of the animal to us by measuring the Doppler shift of the transmission between the transmitter and the satellite. However, this requires that the transmitter is within the cone of reception of the satellite and that several transmission strings be obtained by the satellite as it passes overhead. Since satellites are not always overhead, the information is not in real time and may be several hours old.
Thus, in order to increase our chances of finding an entangled whale for later rescue we employ both VHF and satellite transmitters; allowing the two to compliment each other and provide a measure of duplicity, which overall increase our chances of finding the tagged animal. The satellite transmitter provides us with a broad range and remote means of monitoring the animal (data is sent to CCS computers). Once the satellite information shows that the animal has slowed down in a given area and conditions are right to launch a rescue attempt, the VHF tag, providing real-time and finer grain information, allows us to pinpoint the animal’s whereabouts.
Both VHF and satellite tags only transmit while the animal is at or near the surface, since the transmitters themselves cannot transmit through water. This makes obtaining positions or fixes on whales and other marine mammals difficult since they spend a great deal of their time submerged. To increase the transmission time of the transmitters, the VHF and satellite tags are secured to a special buoy (see photo), which is attached to the whale in much the same way as the kegging buoys – tethered to the entangling gear.
The buoy not only provides the necessary buoyancy to keep the transmitters at the surface for the greatest period of time, but is also durable. It can withstand depths of greater than 1000 feet, forceful contact with the animal itself and the general rigors of the marine environment. The design also maintains its hydrodynamic orientation through the water as it is being towed.