Tagging Studies

Male elephant seal with two tags on its head. The main tag is a satellite tag that allows researchers to track the animal across the ocean. The smaller tag on top is a VHF tag that allows the instrument to be recovered when the animal is on the beach. Photo courtesy of Dan Costa, UC Santa Cruz.

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^[1]LeBoeuf, B. J. (1994). Variation in the Diving Pattern of Northern Elephant Seals with Age, Mass, Sex, and Reproductive Condition. In B. J. LeBoeuf & R. M. Laws (Eds.), Elephant Seals: Population Ecology, Behavior, and Physiology (pp. 237–252). Berkeley, CA: University of California Press..

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^[2]Burgess, W. C., Tyack, P. L., Le Boeuf, B. J., & Costa, D. P. (1998). A programmable acoustic recording tag and first results from free-ranging northern elephant seals. Deep Sea Research Part II: Topical Studies in Oceanography, 45(7), 1327–1351. https://doi.org/10.1016/S0967-0645(98)00032-0. Tags deployed on cetaceans can be attached to the outer layer of skin with suction cups^[3]Johnson, M. P., & Tyack, P. L. (2003). A digital acoustic recording tag for measuring the response of wild marine mammals to sound. IEEE Journal of Oceanic Engineering, 28(1), 3–12. https://doi.org/10.1109/JOE.2002.808212. 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^[4]Nowacek, D. P., Casper, B. M., Wells, R. S., Nowacek, S. M., & Mann, D. A. (2003). Intraspecific and geographic variation of West Indian manatee ( Trichechus manatus spp. ) vocalizations (L). The Journal of the Acoustical Society of America, 114(1), 66–69. https://doi.org/10.1121/1.1582862^[5]Reid, J. P., Bonde, R. K., & O’Shea, T. J. (1995). Reproduction and mortality of radio-tagged and recognizable manatees on the Atlantic coast of Florida (in Population Biology of the Florida Manatee (Trichechus manatus latirostris), Information and Technical Report 1) (pp. 171–191). National Biological Service..

Manatee wearing a belt/tag. This is an animal that has been seen and identified over a number of years during an on-going study at Mote Marine Lab. Photo courtesy of Rachel Nostrom, Mote Marine Laboratory, Manatee Research Program.

One of the newest tags, called the DTAG, records the three-dimensional orientation of an animal with enough detail to detect individual fluke strokes^[6]Johnson, M. P., & Tyack, P. L. (2003). A digital acoustic recording tag for measuring the response of wild marine mammals to sound. IEEE Journal of Oceanic Engineering, 28(1), 3–12. https://doi.org/10.1109/JOE.2002.808212. 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^[7]Nowacek, D. P., Johnson, M. P., Tyack, P. L., Shorter, K. A., McLellan, W. A., & D., A. P. (2001). Buoyant balaenids: the ups and downs of buoyancy in right whales. Proceedings of the Royal Society B: Biological Sciences, 268(1478), 1811–1816. https://doi.org/10.1098/rspb.2001.1730, measure the response of wild marine mammals to sound^[8]Johnson, M. P., & Tyack, P. L. (2003). A digital acoustic recording tag for measuring the response of wild marine mammals to sound. IEEE Journal of Oceanic Engineering, 28(1), 3–12. https://doi.org/10.1109/JOE.2002.808212, and explore the buoyancy of right whales^[9]Nowacek, D. P., Johnson, M. P., Tyack, P. L., Shorter, K. A., McLellan, W. A., & D., A. P. (2001). Buoyant balaenids: the ups and downs of buoyancy in right whales. Proceedings of the Royal Society B: Biological Sciences, 268(1478), 1811–1816. https://doi.org/10.1098/rspb.2001.1730.

A digital tag attached to a right whale’s back using suction cups. Photo courtesy of Peter Tyack and Mark Johnson, Woods Hole Oceanographic Institution. The subject footage was taken under the authority of Scientific Research Permits Nos. #981-1578-01 or 981-1707, issued by the National Marine Fisheries Service to Peter L. Tyack under the authority of the Marine Mammal Protection Act and the Endangered Species Act

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.

Additional Links on DOSITS

• Controlled Exposure Experiments
• Passive Acoustic Recording Tags

Additional Resources

• Tagging of Pacific Pelagics.