Arrays of underwater receivers—attached to floating buoys or moored to the bottom—are used to detect, decode, and store these data. Mary Lee's acoustic device can transmit to receivers up to meters away, which is in the technology's typical range. Scientists periodically visit their underwater receivers to download data from the acoustic tags. Along North America's Atlantic coast, dozens of researchers are acoustically tracking thousands of fish of different species.
Scientists who study red drum Sciaenops ocellatus in east Florida might find ID pings on their underwater receivers from great white sharks tagged by New York scientists, and these data can be shared through the Atlantic Coastal Telemetry Network, a collaborative tracking system.
Acoustic tagging has become particularly important in creating management plans for reef fisheries.
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For instance, Nassau grouper Epinephelus striatus , which is IUCN red listed as endangered, once spawned in large aggregations at dozens of Caribbean reefs during winter full moons. In the s, the reefs were overfished, and numbers of Nassau grouper fell across the region. In , the Cayman Islands government established a no-take zone at one of the Caribbean's last remaining highly productive spawning areas for Nassau grouper.
The no-take zone is located at the west end of Little Cayman Island, one of three islands in the self-governing British territory. But fishers objected to the no-take zone, arguing that the Little Cayman spawners are not local fish but instead Nassau groupers migrating from other countries.
Fishery managers sought to learn the life history of the island's spawning Nassau groupers. Researchers attached acoustic tags to Nassau groupers and installed receivers along the perimeter of mile-long Little Cayman Island, including the productive spawning area on the west end. But the island's Nassau grouper do not swim directly to the west end for winter spawning season.
Instead, they circle the island seven to nine times, traveling hundreds of kilometers and repeatedly visiting a once-productive spawning site at the east end of the island. We believe that the remaining fish on the east side had decided that they would go over to the west side, where all the other fish had aggregated. We think that these spawning sites are connected and might wink in and wink out at different times. So you need to protect more than just one spawning site, and that's why just one no-take zone is not effective.
We ultimately got science that worked into better management for the species moving forward. It's an example of how we can improve our ability to manage a species by collecting basic information about how animals use space.
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The loggerhead's track and her nest were not hard to find—even for a beginner—when you knew where to look. When the turtle reached the beach dune, she dug a hole, laid about eggs, and then used her flippers to flick sand back into the cavity, creating a distinctive small mound over the nest. Then, slowly, she made her way back to the sea. A spawning burst of Nassau groupers at Little Cayman in the Caribbean. This endangered reef species, which reproduces only during the winter full moons, was tagged to track its spawning behavior and learn about its reproduction.
Hope excavated the mound with her hands. When she found the nest chamber, she and local volunteer Jackie Brothers gently took out the eggs and counted them. Brothers refilled the cavity with sand and placed a wire fence around the mound to protect it from raccoons and coyotes. Brothers is one of volunteers who help state, federal, and nongovernmental organization NGO employees document sea-turtle nests on South Carolina beaches each morning during nesting season. This army of beach watchers annually locates about nests and sacrifices a single turtle egg from each one. Hope carried the single turtle egg down the slope of the beach.
She dug a small hole in the intertidal sand. She broke the egg into the hole, then covered it with sand to discourage predators from sniffing around the area. Hope kept the shell for a DNA record, making it an effective genetic tag when the turtle's subsequent nests are located by the volunteer network. Nairn and his colleague Brian Shamblin have documented where a mother nests, the number of nests she lays during each nesting season, and the number of years between nesting seasons. In the past, attaching a metal or plastic tag to a sea turtle's flipper was the only effective method for obtaining reliable demographic data about sea-turtle nesting.
Each tag contained a unique serial number and the address of the organization applying the tags. But sea turtles nest only at night, which presented logistical problems. It is easier, of course, to find a nest at daylight and take an egg for a genetic tag than it is to intercept a loggerhead in the dead of night and read a physical tag. Genetic tagging is also more accurate. But data from genetic tags show that loggerheads actually nest four to five times a season.
About 4 years ago, the population of loggerheads in this recovery region ticked up slightly after a year period of decline. Sea turtles reach sexual maturity when they are about 30 years old. The slightly rising numbers of loggers could be the result of improved tagging techniques. Or it could be the result of sea-turtle protections that began in the s and s, when citizen scientists and natural-resource agencies began monitoring and protecting nests along beachfronts.
Shrimpers were required to attach turtle-excluder devices to their nets, which reduced the number of sea turtles trapped in nets and drowned. Moreover, the shrimping industry has rapidly declined because of cheap seafood imports, which probably reduced the fishing pressure on sea turtles. But it is too early to tell whether conservation efforts have actually increased loggerhead populations.
Kate Mansfield, a sea-turtle researcher at the University of Central Florida, is excited about using a tiny tracking tag in mid This extremely light device—only 5 grams—allows scientists to follow small birds, insects, and juvenile sea turtles that had not been previously tracked by real-time GPS telemetry.
Mansfield studies five species of juvenile sea turtles, ranging in age from about 3 months to a little more than a year.
Researchers once thought that small turtles floated helplessly in currents that carry them, for instance, into the rich algal food resources of the Sargasso Sea. But recent Mansfield studies show that young turtles do swim at times, moving in and out of currents in efforts to find food. Still, finer-scale information about how juvenile turtles are moving is unavailable because more accurate sensors have been too heavy for this age group, she says.
Charlotte Hope, a wildlife biologist left , and volunteer Jackie Brothers sacrificed a single loggerhead sea-turtle Caretta caretta egg from a nest on a South Carolina beach. Photograph: John H. The team hopes to bring down the weight to 1 gram. The International Space Station is only kilometers from the Earth's surface.
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Argos satellites, by contrast, are kilometers away. Because the ICARUS tag does not have to transmit as great a distance, it can use a smaller-powered transmitter and a smaller battery in a smaller tag. It can measure magnetic fields, temperature, pressure, and light intensity.
It also includes a three-dimensional 3-D accelerometer that tracks how much energy an animal uses moment to moment, capturing the duration, intensity, frequency, and other movement patterns. These data are logged and converted into numbers and types of movements, which allows caloric expenditure to be estimated. The new tags could help solve some mysteries about juvenile sea turtles. Two yearling loggerhead sea turtles Caretta caretta carry solar-powered satellite tracking devices in the South Atlantic Ocean as part of a study by the University of Central Florida and Brazil's Projeto Tamar.
Photograph: K. The solar-powered tags provide one data transmission a day with 12 GPS points, as well as the 3-D-acceleration, magnetic field, and temperature data. The 5-gram tag, which enables researchers to monitor animals as small as grams, has an expected lifetime of 1 year. You never know what a technology brings.
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There could be some bugs that are unexpected. But Wikelski is confident that smaller and more powerful tags will alter humanity's relationship to the natural world. If wild animals can tell you information that is useful to you, it could fundamentally change how we conserve them.