CHARLESTON, SOUTH CAROLINA—A surfacing whale is a sight to see, but it would be even more dramatic to watch one ply the ocean depths. Researchers have taken a step closer to doing just that with sophisticated radio-tagging technology and a new computer program that uses the data to recreate a whale's path underwater. The results, presented here yesterday at the annual meeting of the Society for Integrative and Comparative Biology, are helping scientists understand how the school bus-sized beasts are able to take in enough food to sustain their great girth, and how underwater noises, such as sonar, might affect their well-being.
Comparative physiologist Jeremy Goldbogen of the Cascadia Research Collective in Olympia, Washington, studies feeding in blue fin and other so-called rorqual whales. For almost a decade, he and his colleagues have been attaching suction cup radio tags onto the backs of the cetaceans. The tags record depth, sound, and other parameters as the whales swim. After a set amount of time, they fall off, float to the surface, and send out a radio signal so they can be retrieved and their data analyzed.
The work showed that in one giant gulp, a blue whale—the biggest creature on Earth—takes in 125% of its body weight in water and krill. During their dives, the cetaceans ram into patches of krill, opening their mouths wide and wrapping their jaws around prey-laden water, a move that stops them short. Next, they close their mouths and push water through their baleen, a system of plates that filter out the food, then speed up for another feeding bout.
But details about this feeding strategy had been lacking. This past summer, Goldbogen monitored several blue and fin whales with new tag technology that detects the changes in the whales' orientation in space, much like smart phones "know" whether they're held in a horizontal or vertical position and adapt screens accordingly. For the 6 to 24 hours they are attached to the whale, the tags also record depth and sound; from the loudness of the water rushing past a diving whale, researchers can calculate its speed. "We use these sensors to reconstruct what the whales are doing," Goldbogen said.
The new tags show that as they gulp, the whales often twirl around like a corkscrew with surprising agility, Goldbogen reported at the meeting. They also will lunge from all different angles, not just horizontally, as previously thought. "We see these amazing maneuvers," Goldbogen said.
He showed those maneuvers to the audience using video animations made possible by new software from Colin Ware, a computer scientist at the University of New Hampshire in Durham who specializes in visualizing very large amounts of information. The program, "Track Plot," incorporates the tag data and approximates the path of the whale underwater.
In the video to the right, a tagged blue whale dives twice over the course of 19 minutes. The movie shows the whale moving at about 50 times its cruising speed. The first dive, to about 15 meters, takes about 2.5 minutes in real life; the second one, which includes feeding bouts, lasts more than 12 minutes and reaches down to 180 meters, where the whale lunges five times in quick succession, as if it were on a roller coaster.
"It's great that they are doing this," says Douglas Altshuler, an integrative biologist at the University of British Columbia, Vancouver, in Canada. But Altshuler has reservations about the accuracy of the computed paths because there is a dearth of positional data to confirm the whales' course. Goldbogen points out, however, that the course does incorporate GPS coordinates recorded when the whale does surface.
Goldbogen and his colleagues are now using the same approach to better understand whales' responses to sonar, which some believe disorients the animals, causing them to strand on beaches. With a grant from the U.S. Navy, they tag a whale, expose it to simulated military sonar frequencies and another noise within the same frequency band, and watch the whale's reaction, Goldbogen explained.
Preliminary data indicate that the "ping" can make a feeding whale stop its lunge, turn toward the sound, then move away from it, Goldbogen reported. But the effect is temporary, and soon the whale is back prowling for krill, suggesting the animals adapt quickly. "Many experiments will have to be done to determine whether the Navy's use of sonar has an impact," says Michael Dickinson, a neuroscientist at the University of Washington, Seattle. "But the infrastructure is in place that they can gather more data."