When whales feed in the wild, they don't do so in a diverse, Tower of Babel-style set-up. Whales eat with others of their own species along the 150-mile length of Georges Bank, the vast North Atlantic feeding area off Cape Cod and southern Maine.
Researchers made this finding by collecting acoustic information in the area in 2006, and mapping and identifying whale calls. They learned that there were two main clusters of humpback whales along the feeding banks, and minke, fin and blue whales established their own hangout areas in the space between those.
There's also a lot more feeding at night, as whale call numbers bump up then, when herring are forming very dense groups of ready prey. Whale calls are less grouped and less frequent during the day when herring have set off toward the seafloor.
"It's known that different marine mammal species will eat fish, but no one has mapped their simultaneous feeding distributions over these huge scales," study co-author Purnima Ratilal, who has a Ph.D. from MIT and is an associate professor at Northeastern University, said. "Maybe there is some territorialism going on, or maybe they are preferentially selecting these locations based on their different foraging mechanisms. That's material for new research."
The study idea began when Ratilal and her husband Nicholas Makris, a mechanical engineering professor at MIT, led a research cruise to Georges Bank in 2006. Initially, they planned to study herring behavior, but they also used 160 hydrophones to pick up heightened audio in the area. With this sensing technique, they "mapped sound" in the area's shoals over two weeks.
At the same time, they became interested in the cascading whale calls that surrounded them, and they began the recently published research.
"We were hearing these strange haunting sounds in the galley, like an upsweep, then a down-sweep," Makris said. "Purnima recognized these were whale calls, and had all the characteristics of a classic humpback song. At that point, she started the research that led to the current paper in Nature, which she spearheaded."
The scientists were from MIT, Northeastern University, Norway's Institute of Marine Research and the National Oceanic and Atmospheric Administration. The study results were published in the journal Nature.
Follow Catherine Arnold on Twitter at @TreesWhales.
