A Net Made of Bubbles

A Net Made of Bubbles The unusual feeding technique of humpback whales

[by Will Rice]

“Keep an eye out.  They’ve been down about three and a half minutes,” our skipper, Dave Carnes, shouts to us from the wheelhouse. “ There go the birds!”

A STRAGGLE OF GULLS LIFTS OFF THE WATER, all of them drawn to a faint circle that has appeared on the ocean’s surface. Within moments, a massive black head, jaws agape, shoots up through the circle, followed immediately by a half dozen more whales.  The pink of their mouths and the sieve of black baleen plates give a sense of their purpose. Throats stretch like massive beach balls, and water, flashing with the few herring lucky enough to escape, pours from their mouths. 

The whales are bubble net feeding, one of the most complex, and rarest, forms of feeding behavior in the animal kingdom. Only a small percentage of Alaska’s whales have learned the complex choreography of the technique and, although humpbacks range worldwide, this phenomenon occurs only off the coast of Alaska and British Columbia.  The humpbacks we watch have spent their winter in Hawaii, serenading mates, rivals, and tourists—all without eating. A month-long journey has brought them here, to the edge of Chichagof Island, where they will devour enough food, as much as a ton and a half a day, to sustain them for the rest of the year. As massive as they are (up to 45 feet long, weighing 40 tons), humpback whales feed only on prey small enough to slide down their grapefruit-sized gullets, primarily krill and herring–sized fish.

We watch the whales repeat this performance for about 20 minutes, at times surfacing close enough to see the barnacles that pockmark their skin. Their mouths close, and the whales slip down into the water, rolling onto their sides so their 12-foot pectoral fins jut up from the water’s surface, looking like the airfoil sails of high-tech sailboats. The surviving herring escape to the dark safety of deep water, rejoining the swirling silver shoal of fish fleeing the whales. The whales move slowly along the surface, their breath showing as white plumes against the dark spruce background. A half dozen blows, and they each sound, their white-splotched flukes raised vertically in the air. The drama is about to repeat.

Below us, unseen, the whales search for the escaping herring. Once they locate the prey, one of the whales sets the trap, a ring of bubbles that may range from 15 to 100 feet in diameter, depending on the size of the pod. The physics of bubbles means that the net must be blown within 200 feet of the surface; typically well above the shoal of herring, which may be a thousand feet deep. At least one of the whales dives below the herring and vocalizes, its call becoming a sonic weapon. Whales are the loudest animals on earth, and humpback calls can exceed 180 decibels, loud enough to burst a human eardrum. We cannot hear it above the surface, but the herring, stunned and disoriented, flee upward. The pod circles the panicked fish, using sound, their bodies, and their massive pectoral fins to keep the herring bunched into a mass and forcing them upward into the net of bubbles and jaws.

Our first sign of the underwater drama is a couple of desperately leaping salmon, their own herring feast interrupted. Underwater, the noise and the glitter of the bubbles hold the baitfish in a tight ball, trapped against the surface. The first panicked herring begin to jump, drawing the gulls closer. On a signal from the leader, the whales once again burst through the bubble net. The 20 or so pleats behind their lower jaw relax, allowing their throats to expand enough to capture over 5,000 gallons of water, together with hundreds of unlucky fish. A massive tongue forces the water through the 400 plates of baleen that hang from the whale’s upper jaw, straining the herring from the seawater. Gulls swoop in to pick off the survivors. The whales hang suspended for the moment, and as gravity prevails, one of them, his head still above the water, lets out a massive bellow that echoes off the surrounding mountains. The whales catch their breath, and the dance continues.

Finding a pod of bubble net feeding whales is a highlight of any marine trip, but there are no guarantees. The technique has been observed from Ketchikan to Seward, but the whales follow the herring, and the specific locations they frequent can change from year to year. When you do find them, as we did while cruising Chatham Strait, one of the most consistent feeding areas in Alaska—count yourself lucky. You’re bearing witness to one of the most unique and evolved wildlife displays in the world.

Will Rice came to Alaska for the summer in 1970 and never left. More of his photos can be seen at willricephoto.com.

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