October 18, 2012
Researchers Use Underwater Robot To Track Tagged Sharks
Lawrence LeBlond for redOrbit.com - Your Universe Online
Researchers from University of Delaware are in the midst of a multiyear study with Delaware State University researchers to better understand the behavior and migration patterns of sand tiger sharks. In the latest phase of the study, an underwater robot is being unleashed to hunt down and follow these seemingly placid predators.
The Oceanographic Telemetry Identification Sensor (OTIS) is a remote-controlled underwater device that looks very much like a yellow torpedo. Normally used for testing water conditions, the researchers have outfitted OTIS with acoustic receivers that can recognize signals given off by transmitters. OTIS will track sharks that have been previously tagged with these transmitters as they travel through their coastal habitat.
Matthew Oliver, assistant professor of oceanography in UD´s College of Earth, Ocean, and Environment, said OTIS has, “in the past week“¦detected multiple sand tiger sharks off the coast of Maryland that were tagged over the past several years.”
“This is the first time that a glider has found tagged sharks and reported their location in real time,” he said in a news release, reported by Teresa Messmore, a Communications Specialist for UD´s College of Earth, Ocean, and Environment.
The technology implemented allows the course of OTIS to be changed, enabling it to follow the sharks and test the water around them. Using OTIS to track these sharks will allow scientists to follow where the sharks are going more efficiently than using conventional tracking methods.
OTIS will be tracking sharks with three different types of tags.
One is an acoustic transmitter that “pings” receivers while passing by a set of 70 devices situated around Delaware Bay. DSU´s Dewayne Fox maintains these receivers, and has tagged more than 500 sharks since 2006.
Another tracking mechanism implemented is the pop-off satellite archival tag. The team is using 34 of these tags, which store data on the sharks´ journeys for up to a year then automatically release from the animal to dispatch a location signal for retrieval.
A third type of tag, also the newest, is called a VEMCO mobile transceiver (VMT). This tag is larger than the others, but also transmits and receives information to communicate its location and listen for the pings of other marine animals outfitted with acoustic tags.
The VMT tag “will tell us not only where it is, but who it´s with,” said Oliver. “It´s like a social network for sharks.”
Oliver, Fox and students from both universities, spent the summer catching sand tiger sharks, carefully pulling them into stretchers alongside their boat, and inserted transmitters through a quick surgery.
Sand tiger sharks are the largest commonly occurring shark in Delaware´s bay and coastal region. Although these marine animals are generally slow-moving and seem relatively placid, they are apex predators in their habitat and play a key role in the ecological balance of the region.
“Sand tigers have suffered from a number of threats that ultimately led to population declines,” said DSU´s Fox. “In 1997 sand tigers were listed as a ℠species of concern´ by the National Marine Fisheries Service, although very little is known of their migrations and habitat requirements.”
Scientists have suspected that these sharks migrate widely along the Eastern Seaboard, and using newly collected information, the university teams plan to map these habitats, cross-referencing shark data with satellite and remotely sensed environmental conditions to create a comprehensive picture of the animals´ habitats.
Oliver told Messmore the teams are integrating two areas of biotelemetry to get a better understanding of the behaviors of migration patterns of these apex predators.
Fox is part of the Atlantic Cooperative Telemetry Network (ACT), which tracks thousands of animals up and down the coast; Oliver participates in the Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS), which uses satellites, underwater robots and models to study the coastal ocean.
By combining the two unique data sets, Oliver and Fox hope they will assist natural resource managers in predicting where sand tiger sharks live and how best to handle conservation efforts.
OTIS will be a big part of this, helping researchers find out which water conditions sharks prefer to swim in during their migrations. OTIS is capable of traveling much further out than what the static receivers´ can pick up, and can also collect information on a wide array of conditions, including water temperature, quality, clarity and oxygen levels.
The team hopes the data will give scientists a little more understanding as to why these sharks head to certain places, explained Oliver.
Oliver said the team took an educated guess as to where these sharks were currently hanging out last week when it launched OTIS for the first time. They launched it off the coast of Delaware´s Indian River Inlet and heading south. After five days, they began receiving transmissions from sharks about 4 to 9 miles off the coast of Assateague Island, Maryland.
Their next goal is to direct the glider to stay near the sharks, unless they move south of the lower Delmarva Peninsula. OTIS can last up to four weeks without recharging.
“We have at least another two weeks of battery,” Oliver said. “We´ll see how it develops.”