WOODS HOLE, Mass. — When the whale known as Touche is hungry for a school of fatty fish, he circles below them, fashioning a net of air by streaming bubbles from his blowhole. Then he corkscrews toward the surface of the Gulf of Maine, herding the fish into an ever tighter packet with the bubbles and his 30-ton body. Finally he opens his jaw wide, takes a monstrous gulp and relaxes, breathing deeply at the water’s surface.
Then he dives again. Over and over.
Touche’s feeding strategy, captured in June by an electronic tag attached to his back, is of keen interest to scientists tracking North Atlantic humpback whales off Cape Cod.
“Every time we go out and put another tag on, we learn something else," said Dave Wiley, research director of the Stellwagen Bank National Marine Sanctuary in Massachusetts, who returned to shore recently after plying its waters for two weeks with researchers from several institutions.
For Wiley, the most striking insight is that each humpback has its own set of behaviors, often confounding efforts to generalize about the species.
“We’ve got examples sometimes of hundreds of feeding events that are almost all identical for that particular whale but are different than the hundred feeding events that we have for a different whale," he said.
As a result, Wiley’s papers about the humpback are full of caveats.
“It’s frustrating and complicated and fascinating all at the same time," he said.
More broadly, he and his colleagues hope to use their findings to push for changes in fishing and shipping rules to protect the humpbacks.
The Stellwagen sanctuary is prime habitat for a pencil-size schooling fish called the sandlance that draws a host of predators, from the humpbacks to fin whales, minke whales, dolphins, striped bass and bluefin tuna.
Yet the sanctuary’s proximity to land — 25 miles from Boston and three miles from the tip of Cape Cod — also means it is heavily used by humans.
On a bright summer day, its waters may be packed with half a dozen whale-watching boats and thousands of recreational and commercial fishing vessels, sailboats and yachts — and that’s just at the surface. The depths abound with ropes connecting strings of lobster pots and webs of fixed fishing gear that stretch across like tennis nets.
Most human-caused deaths of humpbacks occur when whales are struck by passing ships or become entangled in fishing gear, Wiley said. But policymakers could not reduce the risks because they did not know enough about how the whales move underwater.
“Our whole goal is to collect data to influence policy," Wiley said.
A growing database
For decades, humpback behavior was poorly understood because of the difficulty of shadowing the whales as they roamed the North Atlantic. The breakthrough was the DTAG, engineered in 1999 at the Woods Hole Oceanographic Institution in Massachusetts.
Unlike satellite tags, which transmit location, typically over a long period of time, DTAGs stay attached for 36 hours at most and record information like speed, depth and audio. They also carry a three-axis accelerometer that measures the front-to-back, side-to-side orientation of the whale.
Heading out for two weeks each summer since 2002, Wiley and a handful of colleagues have successfully tagged humpbacks 90 times, in some cases the same individuals over multiple years. The tag data is overlaid with acoustical studies of prey biomass and, for the last two summers, images from National Geographic’s so-called Crittercams, which bring back video showing how whales use different parts of their bodies while feeding and coordinate their movements while traveling in groups.
Last month, the taste of success was in the salty air as Wiley’s team unloaded its gear from the 187-foot research vessel. In two weeks, they had tagged 21 humpback whales and identified about 160 individuals, adding a wealth of information to a decade’s worth of observations.
“We probably have one of the largest databases for fine-scale foraging behavior of anywhere in the world at this point," he said.
A research revolution
The data has revolutionized humpback research and conservation in the sanctuary, showing scientists where the whales spend their time in the water column while on a dive, what they do at different depths, how they move around and when they vocalize.
“The DTAG is sort of a revelation and a revolution," said Ari Friedlaender, a marine ecologist at Duke University who has taken part in the Stellwagen project since 2006.
Conventional satellite tags, while deployed for longer periods, “only give you a position when the animal comes to the surface," he said. “The DTAG measures the orientation of the whale 50 times a second as well as the audio — everything the animal hears and every sound the animal is making."
The tag, about the size of a pack of Twinkies, has four suction cups and is attached to a whale by extending a pole.
The tag is programmed to pop off after a predetermined amount of time, although some get bumped off or shaken off early. Then it floats to the surface, where the researchers retrieve it and download its data.