Visual observations provide information about the behavior of animals when they are at the surface, but how do scientists study animals' behavior underwater? One way is to attach instruments, called tags, to marine animals. The tags provide information on what the animals are doing when they are underwater. They also allow scientists to track the animals when they are at the surface. Tags can provide long-term continuous information on the behavior and movements of individual animals.
Tags contain a variety of sensors for recording marine animal behavior. Time-depth recorders provide information about dive times and depths, as well as time spent at the surface. Accelerometers and compasses measure the animal's orientation and heading. Hydrophones pick up both the sounds to which the animals are exposed and the sounds that they produce. Video cameras record underwater images and provide information about the animal's surroundings. Global Positioning System (GPS) receivers provide geographic position information when the animals are on the surface. Some tags store the data internally. The data can be recovered when the tags come off. Other tags use transmitters (radio, ultrasonic or satellite) to relay data back to the researchers via computer technology and enable tracking and observations of the animal when it surfaces. Tagging technologies are rapidly advancing as electronics become smaller.
Depending on the species, tags can be attached to the animals in many different ways. Pinnipeds are often captured temporarily so that a tag can be glued to the outer layer of fur. Tags deployed on cetaceans can be attached to the outer layer of skin with suction cups. Like pinnipeds, manatees are temporarily captured and can be fitted with a belt that goes around the base of the tail. Sensor packages can then be either tethered to the belt or placed directly on the belt .
One of the newest tags, called the DTAG, records the three-dimensional orientation of an animal with enough detail to detect individual fluke strokes. This tag also includes a hydrophone so scientists can correlate the sounds an animal is exposed to with its behavior. The DTAG has been used to examine the variation in manatee vocalizations, measure the response of wild marine mammals to sound, and explore the buoyancy of right whales.
Tags equipped with hydrophones can provide detailed information about both animal behavior and sound exposure. Using such tags in controlled exposure experiments can help determine cause and effect relationships between sound exposure and marine mammal responses.
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