How Do We Track Manatees?
Manatees are tagged by the Florida Fish and Wildlife Conservation Commission (FWC) to answer specific research questions of importance to conservation and management of this imperiled species. Authority to capture and tag manatees is granted to FWC through a permit from the federal U.S. Fish and Wildlife Service.
Typically, manatees are captured and receive a health assessment on site before being tagged and released for a research project. This provides an opportunity for researchers to assess the health of the individual prior to inclusion in the research study and to ensure the best fit of the tagging gear. Standard capture techniques using nets deployed from a specialized manatee capture/rescue vessel have been employed since the 1990s. Manatee captures can occur in open water or alongshore. Typically, an aerial observer flying in a single-engine Cessna airplane locates individual manatees and guides the capture boat captain in setting the net. This increases the efficiency and safety of capture operations. Other vessels wait nearby to collect data on the capture attempts, to carry gear, and to provide assistance if needed. The crew aboard the capture boat is made up of a team of people with experience in the capture and handling of large marine mammals. After capture, the manatee can either remain aboard the capture boat or be moved to land for the health assessment and application of tagging gear.
Manatee health assessments are typically conducted in collaboration with other agency and university partners, including the University of Florida’s Aquatic Animal Health Program and the U. S. Geological Survey’s Sirenia Project. Data collected during these assessments contribute to many research studies focusing on manatee health and physiology and provide valuable insights into the overall health of the population. Manatee health assessments usually include:
- Morphometrics (measuring lengths and girths) and weight
- Backfat thickness, measured with an ultrasound instrument
- Blood chemistry and hematology
- Collection of urine and fecal samples
- Collection of a skin sample and blood for genetic analyses
- Photo-documentation of scars, wounds, and lesions
- Assessment of body condition
- Pregnancy test for mature, non-lactating females
- Monitoring of blood gases and vital signs including heart rate, respiration rate, and oral temperature
- A descriptive clinical assessment by a veterinarian experienced in assessing and treating manatees.
Individuals are scanned for the presence of Passive Integrated Transponder (PIT) tags; if none are present, two are inserted just below the skin to aid in future identification. These PIT tags, commonly referred to as microchips, are about the size of a rice grain and are widely used by veterinarians to help in identification and return of lost pets.
Manatee Tagging and Release
Manatee tagging gear consists of a padded belt, a flexible tether, and a floating radio-tag. The belt is fit around the manatee’s peduncle (where the main body meets the tail) using a buckle and nylon webbing that allow for a custom fit to the girth of the individual. Smaller animals are tagged with weaker belts that can break more easily, whereas larger animals are tagged with stronger belts. The buckle also acts as the point of attachment for the four- or five-foot-long flexible tether. Because manatees are coastal animals that feed in shallow seagrass beds, the length of the tether is specifically designed to allow the floating tag to transmit and receive radio signals when the animal is at depths up to six feet. While the flexible tether is also designed to avoid entanglement, a safety feature (called a weak link) is built into the base of the tether so that it can break free if the tag becomes caught. An ultrasonic beacon is incorporated into each belt to facilitate field tracking (with a sonic receiver and hydrophone) and relocation should the tether detach at the weak link and the belt remain on the manatee. During winter studies, a small temperature logger is secured to the base of the tether to gather information on the water temperatures experienced by the manatee.
The floating tag contains three essential components: a GPS unit, a satellite transmitter, and a VHF transmitter. The GPS unit functions similarly to GPS units found in car navigation systems or your cell phone, accurately determining the location of the tag. These GPS units can be programmed to acquire a location at any time interval and store that information in their memory; for example, a 15-minute GPS fix interval can provide up to 96 locations per day for up to 6 months. The satellite-linked UHF transmitter, technically referred to as a platform transmitter terminal or PTT, sends these GPS locations—along with data on tag activity, temperature, and diving behavior—to orbiting satellites through the Argos satellite system. Argos is a Low Earth Orbit global satellite-based location and data collection system dedicated to studying and protecting our planet's environment. Manatee researchers view and download these data through a website, permitting remote monitoring of individual manatee movements in close to real-time! The Argos-linked GPS tags provide a tremendous amount of high-quality data on manatee movements and habitat use.
Once the health assessment and tagging are complete, the manatee is placed in a stretcher and released just off shore. In some situations, a manatee that has been successfully rehabilitated in captivity will be tagged just before it is released back into the wild. Visit the Manatee Rescue and Rehabilitation Partnership website to learn more about tagged, rehabilitated manatees.
For more photographs of the manatee capture and tagging operation, visit the Manatee Capture and Tagging FWC Flickr photo album.
Tracking Manatees in the Field
The VHF transmitter allows scientists to locate manatees in the field. Each tag transmits a unique VHF frequency; much like you tune your car radio to a specific radio station, we can tune our tracking receiver to a specific manatee tag. Unique color band combinations on the float of each tag are used for visual identification of individual manatees. VHF signals cannot be transmitted through saltwater. Therefore, when the tag is pulled underwater during traveling or while bottom resting in deeper water, we cannot receive that VHF signal, making it more difficult to home in on the tag. However, if we know the specific area (within several hundred meters) in which the manatee is located, we can use the ultrasonic beacon in the belt to locate the individual.
Directly observing the tagged manatees in the field allows biologists to document behavior patterns, associations with other manatees, features of the habitat, and reproductive success of females. Such observations provide insights into why manatees visit particular sites; for example, to drink from sources of freshwater. The tagging assembly does not harm the animal or affect its behavior. The belt is padded so it fits comfortably around the peduncle, and the tag is buoyant which allows the animal to feed or rest with the tag at the surface. Manatees with tags behave just like untagged manatees; they migrate long distances, feed, socialize, mate, give birth, and raise calves.
We make every attempt to ensure that the tagging gear is removed from the animals at the end of the study. A programmable breakaway release unit is incorporated into many of the belts as a means to automatically release all of the gear from the animal at a pre-programmed date and time; this permits staff to easily retrieve the tag and belt assembly without approaching the manatee. Otherwise, a researcher quietly approaches the tagged manatee and cuts off the belt with a custom-made pole-mounted tool. As a further precaution, nuts and bolts used in the construction of the belt corrode in salt water, allowing the belt to detach from the manatee if it is not relocated.
For more photographs of manatee behavior field research, visit the Manatee Tracking and Behavior Flickr photo album.