January 10, 2013
Marine Gliders Pick Up Songs From Endangered Whales In The Gulf Of Maine
redOrbit Staff & Wire Reports - Your Universe Online
Two underwater robots with instruments that detect the calls of baleen whales heard the ℠songs´ of nine critically endangered North Atlantic right whales in the Gulf of Maine in December, scientists reported on Wednesday.
Right whales, which can weigh as much as 140,000 pounds and grow up to 55 feet in length, are thought to use the area every year between November and January as a mating ground, said researchers from Woods Hole Oceanographic Institution (WHOI), who led the initiative.
Only 300 to 400 of the endangered whales are believed to exist, according to the National Oceanic and Atmospheric Association (NOAA), the agency charged with enforcing the Marine Mammal Protection Act.
The WHOI robots were able to transmit the detections of the whales in real-time to land-based researchers, representing the first successful use of technology to report detections of several species of baleen whales from autonomous vehicles.
WHOI researchers Mark Baumgartner and Dave Fratantoni reported their discovery to NOAA, which established a “dynamic management area,” asking mariners to slow their vessels to avoid hitting the mammals.
The marine robots, known as gliders, were equipped with a digital acoustic monitoring (DMON) instrument and customized software that allowed the vehicle to detect and classify calls from four species of baleen whales: sei, fin, humpback, and right whales.
The project took place from November 12 through December 5, operating in an area known as the Outer Fall, about sixty miles south of Bar Harbor, Maine, and 90 miles northeast of Portsmouth, NH.
Two gliders were launched from the University of New Hampshire´s 50-ft research vessel, the Gulf Challenger.
The vehicles studied the area for two weeks, and sent data back to researchers every two hours via satellite until the WHOI team arrived on the University of Rhode Island´s research vessel Endeavor on November 28.
The gliders continued to survey for another week until they were recovered by the Endeavor on December 4.
“We put two gliders out in the central Gulf of Maine to find whales for us,” said Mark Baumgartner, a WHOI researcher specializing in baleen whale and zooplankton ecology.
“They reported hearing whales within hours of hitting the water. They did their job perfectly.”
Utilizing the gliders´ reconnaissance data and continued real-time updates, the researchers were able to locate whales within just a few hours.
“We found our first right whale on the first day that we were surveying in decent weather conditions because the gliders were up there doing the leg work for us, to tell us where the animals were in real time,” Baumgartner said.
The new whale detection system gives conservation managers an innovative, cost-effective alternative to ship- or plane-based methods to identify the presence of whales. It may also help whale researchers better understand why the marine mammals are attracted to this part of the Atlantic during the late fall and winter. Researchers have struggled to study this phenomenon due to the area´s high winds and rough seas in late fall.
“This presents a huge knowledge gap,” said Baumgartner, adding that the labor-intensive task of surveying for whales is typically done by human observers on ships or airplanes, and is limited by the conditions at sea.
“We´ve been doing visual based surveys for a long time — either from a plane or a boat. They have a lot of value, but they are limited, especially at certain times of the year,” said Sofie Van Parijs, leader of the Passive Acoustic Research Group at NOAA´s Northeast Fisheries Science Center (NEFSC).
“These gliders provide a great complement to this system. Knowing where right whales are helps you manage interactions between an endangered species and the human activities that impact those species.”
The WHOI project is the result of a multi-year collaboration among scientists at WHOI and the NEFSC Protected Species Branch in Woods Hole, with federal funds provided by the Office of Naval Research and NOAA´s Applied Science and Technology Working Group Program.
“No one of us could've done this project alone. But by teaming up, we created a really nice group of people with expertise that was tailor made for this problem,” said Baumgartner.
“Now, we can know that there's an animal in a particular part of the ocean within hours of a call being made, as opposed to months later,” when the instruments have finally been retrieved and the data has been analyzed.
The six-foot long, battery-powered gliders employed in the study have been in use by oceanographers for about a decade. The torpedo-shaped vehicles move up, down, and laterally in a sawtooth motion by alternating their buoyancy. Short ℠wings´ provide the needed lift.
The gliders are remarkably quiet in the water, and have an underwater microphone on their underside and an iridium satellite antenna on their tail sections. The vehicles surface every few hours to get a GPS position and transmit data to land-based servers.
The gliders were also equipped with a specialized digital acoustic monitoring (DMON) instrument — a circuit board and battery about the size of an iPhone — which used recorded audio to generate spectrograms, a form of the audio that facilitates complex sound analysis.
Baumgartner designed special software that uses the spectrograms to generate a “pitch track,” a visual representation of a whale call that can predict which species of whale made the call.
Tallies of each species´ detected calls, and even a small subset of detected pitch tracks, can then be transmitted to shore by the glider.
“Each pitch track takes less than 100 bytes, whereas transmitting just one of those calls as an audio clip would take about 8000 bytes of data,” said Baumgartner, adding that this makes the system both flexible, efficient and economical.
In addition to demonstrating the value of the robots for the management and conservation of baleen whales, the project also has ongoing scientific objectives, such as obtaining measurements and biological samples of the tiny crustaceans or zooplankton upon which the whales feed.
These samples can help scientists characterize the oceanic conditions, and better understand how those conditions impact the whale´s food and attract the whales to the area.
“Untangling how that happens is a big deal,” said Dave Fratantoni, a physical oceanographer with WHOI.
“We wanted to figure out what right whales were feeding on in this area,” said Baumgartner.
“We took profiles of the temperature and the salinity of the water and sampled zooplankton throughout the water column to understand what might make this area attractive to right whales.”
Analysis of these data is currently underway.
Representatives from the New England Aquarium, who maintain a catalog of right whales and are experts in identifying individual right whales from patches of thickened skin on their heads, were also involved in the project.
The team was able to recognize four of the individual whales sighted during their week on the research ship -- two males born in 2006, one male born in 2004, and one female born in 2008.