Two submarine robots equipped with instruments designed to “listen” for the calls of baleen whales have detected nine endangered North Atlantic right whales in the Gulf of Maine.
The project employed ocean-going robots called gliders equipped with a digital acoustic monitoring (DMON) instrument and specialised software allowing the vehicle to detect and classify calls from four species of baleen whales – sei, fin, humpback and right whales. The gliders’s real-time communication capabilities alerted scientists to the presence of whales in the research area, in the first successful use of technology to report detections of several species of baleen whales from autonomous vehicles.
Using the gliders’s reconnaissance data and continued real-time updates, the science team was able to locate whales in just a few hours of searching. “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,” says Woods Hole Oceanographic Institution (WHOI) scientist Mark Baumgartner.
The innovative whale detection system provides conservation managers with a cost-effective alternative to ship- or plane-based means of identifying the presence of whales, and gives whale ecologists new tools for understanding large animals that spend most of their lives out of human eyesight below the sea surface.
Whale researchers want to learn what draws whales to this part of the ocean during the late fall and winter. However, high winds and rough seas typical of that time of year make studying the animals very difficult.
“This presents a huge knowledge gap,” says Baumgartner.
The labor-intensive work of surveying for whales, overseen by NOAA, is usually 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,” says 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.”
Gliders – approximately six-foot-long, torpedo-shaped autonomous vehicles with short wings – have been in use by oceanographers for about a decade. They move up, down, and laterally in a sawtooth pattern through the water by changing their buoyancy and using their wings to provide lift. Battery powered and exceptionally quiet in the water, the gliders are equipped with an underwater microphone on the underside of the vehicle near its wings and an iridium satellite antenna on the tail section. The vehicle surfaces every few hours to get a GPS position and transmit data to shore-side computers.
The DMON – a circuit board and battery about the size of an iPhone – sits inside the glider recording audio and generating spectrograms, a form of the audio that facilitates complex sound analysis. From the spectrogram, Baumgartner’s software generates a “pitch track,” a visual representation of a whale call, and estimates which species of whale made the call based on characteristics of the pitch track. Tallies of each species’ detected calls and even a small subset of detected pitch tracks can be transmitted to shore by the vehicle. “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,” says Baumgartner. This makes the system efficient and economical. And, adds Baumgartner, it’s also really flexible. It is easy to update the software to include a larger repertoire of whale calls into the software’s “call library.”
The researchers reported the presence of the whales to NOAA, the agency responsible for enforcing the Marine Mammal Protection Act. NOAA put in place a “dynamic management area”, asking mariners to voluntarily slow their vessel speed to avoid striking the animals.
Woods Hole Oceanographic Institute