It's their 15- to 18-foot-long pectoral fins that distinguish humpbacks from all other whales. In fact, the first half of their scientific name, Megaptera novaeangliae, means "big-winged" in Latin. These exceptionally long, winglike flippers, the longest of any whale, give humpbacks the unique ability to make extremely rapid and tight turns. This unparalleled ability to maneuver underwater is critical to the humpback's most dramatic means of capturing prey—bubble-net feeding. It was for a chance to witness this unique and spectacular feeding behavior that I had made my pilgrimage to Southeast Alaska.
It turns out that Sharpe has helped science to better understand several key components of bubble-net feeding. For years whale scientists had wondered why humpback flippers are always completely white on their undersides. The dorsal side of their flippers can range from all white to fully black or any Franz Kline-like combination between the two, but the undersides are invariably as white as porcelain. Through a series of ingenious experiments, Sharpe discovered that humpbacks flash the white side of their fins to scare—and herd—fish. It's important that humpback whales be able to direct schools of small fish because they are toothless filter feeders. They use the bristly plates of baleen that line the perimeter of their upper jaws to strain seawater and to catch fish and other tiny animals on which they feed. So Sharpe's observations proved to be something of a breakthrough in understanding humpback feeding strategies.
Amazingly, humpbacks in Southeast Alaska will sometimes collaborate to feed on schools of herring. Anywhere from two to two-dozen whales will drive herring toward the surface by swimming beneath a herring school while perhaps flashing the white undersides of their flippers. Next, one of the whales will begin circling the fish while releasing a stream of air from its blowhole. The ring of air transforms into a curtain of bubbles as it rises in the water column, acting as a barrier the fish won't cross.
Next, the whales somehow coordinate their movements so that they all enter the column of bubbles at the bottom and begin swimming toward the surface, like a piston rising in a cylinder. The fish constrained inside the bubble net are pinned against the surface by the ascending whales. The whales propel themselves upward with powerful thrusts of their flukes and then open their jaws in unison just before breaking the surface. Their mouths immediately engulf tons of fish-filled seawater as their accordion-like throat pouches swell like overinflated bellows. The whales then snap their jaws shut, trapping thousands of herring inside their maws. By contracting their throat pouches, the whales begin to expel the seawater in their mouths through their baleen, which acts as a giant sieve trapping the herring. Then, the whales use their tongues to lick their baleen clean and swallow hundreds of pounds of fish down throats no larger in diameter than a grapefruit.
This is how it all works in theory, however. After long imagining what it would be like to see a group of bubble-net-feeding humpbacks, I was about to have a ringside seat to the real thing. I was sitting with Sharpe and three other passengers from the Catalyst in a small inflatable boat that he used for close-up observation of feeding whales. The water was flat calm, and we were basking in the warm afternoon sun while silently admiring the backdrop of snow-glazed peaks. Hanging over the side of the boat was a hydrophone, or underwater microphone, which would let us hear the calls of the whales when they began to herd a school of fish somewhere in the depths below.
Sharpe told us that the gulls circling above our heads would give us a clear signal as to where the whales would emerge, as they would be the first to sight the whales' bubble net as it reached the surface. Over the years, gulls have learned that by positioning themselves inside this circle of bubbles, they will get a chance to catch herring as they leap from the water in a last-ditch attempt to escape the whales that are pursuing them from below. When the gulls spot a bubble net, they make a beeline for it, and our plan was to follow their lead.
When the gulls wheeling overhead suddenly increased their cries and made for a spot about a hundred yards closer to shore, we quickly retrieved our hydrophone and followed as fast as we could. As we approached the place where the birds had gathered, we could see that the water was being disturbed, as if someone had turned on Jacuzzi jets just below the surface. We deployed our hydrophone and stared transfixed at an arcing trail of bubbles that was steadily emerging at the surface. As the circle of bubbles was about to close, we could hear the cries from the hydrophone suddenly stop. There was an ominous moment of silence as we awaited the appearance of the whales.
This is where words fail—watching a dozen humpbacks simultaneously erupt into near view is a startling experience that cannot be captured in writing or fully comprehended with one's imagination. First, you see the smooth water on the inside of the bubble net begin to boil as masses of herring dart about just beneath the surface. Scores of fish begin to leap from the water like a fusillade of silvery rockets. Then the whales' knobby upper jaws slice out of the water, and you hear thunderous reports as the leviathans exhale in quick succession. Next, the whole pool of water contained inside the bubble net seems to elevate magically as the whales bring their lower jaws up through the surface. The impossibility of raising such a massive amount of water stands at odds with what you are witnessing, as the whales perform a feat of levitation that seems to defy the laws of physics. Then, the whales clamp their jaws shut and submerge from view, and the whole spectacle is suddenly over.
A century ago, John Muir, naturalist and founder of the Sierra Club, wrote about his experiences with humpback whales in these very same waters. My whale encounters here have given me a profound appreciation of his words:
And yonder, glistening amid the irised spray, is a still more striking revelation of warm life.... a half-dozen whales, their broad backs like glaciated bosses of granite heaving aloft in near view, spouting lustily, drawing a long breath and plunging down home in colossal health and comfort.... One cannot but feel sympathy with and be proud of these brave neighbors, fellow citizens in the commonwealth of the world....