Calls From the Deep

by Rachel Muehlenberg
Photo: Bruce Whittington
The morning is chilling. Everyone gathers on deck, bundled in their sweaters and fleece, scanning the water line. Our hydrophone―a microphone designed to listen and record sounds underwater―picks up a ghostly howl echoing through the deep. Everyone is silent, perplexed at the sound ringing through the speaker. The calls are getting louder, anticipation building. Someone spots a circle of bubbles boiling at the water's surface. Silence engulfs us, leaving us in a disoriented trance. A few electrifying seconds pass… then a group of humpback whales breaks from the center of the bubble ring, mouths wide open. In one fell swoop, hundreds of pacific herring have met their doom. 

We’ve just witnessed the complex, cooperative feeding technique―called bubble-net feeding― used by humpback whales. Humpbacks are a migratory species, spending half the calendar year in warm waters near the equator and the other half of the year in cold waters near the poles. Feeding opportunities for humpback whales take place in colder oceans as the cold-water climate supports their various types of feed, such as pacific herring, mackerel, capelin, and tiny crustaceans like krill and phytoplankton. Needing to consume 4,400-5,500 pounds of feed per day, some humpback whales have developed the bubble-net feeding technique as a way to increase the success rate of their feeding endeavors by working in groups rather than pursuing mass schools of fish on their own.

Bubble-net feeding is a humpback whale group exercise. Group sizes can range from two or three whales up to sixty. Humpbacks use vocalizations to disorient their prey while one whale swims ahead of the group to create the ‘bubble-net’ by exhaling vast quantities of air underwater in a circular formation. The rest of the group follows close behind, vocalizing all the way to corral large schools of fish into the bubbles. Together, they then swim through the bubble-net with mouths agape, taking in large quantities of bewildered prey. Bubble-net feeding is not used by all humpback whales around the world, suggesting that the technique is learned, not instinctual.

Bellies full, the humpbacks try to catch their breath. Over and over, they break the surface with mighty exhalations, expelling spouts of warm air that reach as far as ten feet above the water line. With each inhale, we better understand the immensity of these colossal creatures. The group reconfigures. One by one, they disappear, as if waving us goodbye with their great tails, pulling us with envy into their mysterious world below. We’re left with the ephemeral beauty of watermarks showing their first kick towards the depths. A faraway cry sounds in the deep. Everyone resumes position on deck, awaiting the next surfacing. 

What Bluewater Adventures itineraries are provide the best chance to witness bubble-net feeding?
Ask us here.