Humpback whales need to eat a lot every day, and some even use their flippers to help snag a big mouthful of fish.

Researchers filmed humpbacks (Megaptera novaeangliae) hunting with this tactic, called pectoral herding, off the Alaskan coast. It’s the first time that this behavior has been documented in such detail, the team reports October 16 in Royal Society Open Science.

Humpbacks often feed by lunging with their mouths open to catch any fish in their path. Sometimes, the whales will swim in an upward spiral and blow bubbles underwater, creating a circular “net” of bubbles that makes it harder for fish to escape (SN: 10/20/15). “But there’s so much you can’t see while you’re looking at these animals, standing on a boat,” says Madison Kosma, a whale biologist at the University of Alaska Fairbanks.

Humpbacks sometimes blow bubbles underwater, creating a circular “net” of bubbles that makes it harder for fish to escape. Now a new study documents the whales using their flippers and these nets to help catch fish. In the horizontal version of this tactic, called pectoral herding, whales at the ocean’s surface splash a flipper to strengthen weak parts of a disintegrating bubble net (first clip). In vertical pectoral herding, whales raise their flippers in a “V” formation while ascending through the net to guide fish into their mouths (second clip). The research was recorded under NOAA permits #14122 and #18529.

The researchers got a better view of the whales feeding at the ocean’s surface by flying a drone over the water or extending a video camera attached to a pole from the walkways of floating salmon hatcheries. Over the three-year study from 2016 to 2018, the team noticed that two whales repeatedly consolidated fish inside bubble nets using their two long, pectoral flippers.

In horizontal pectoral herding, whales blew a bubble net before splashing a flipper at weak parts of the net to reinforce the barrier. In vertical pectoral herding, whales created a bubble net and then raised their flippers — like a referee signaling a touchdown — as they ascended up through the net from deeper water, helping guide fish into their mouths. What’s more, the whales sometimes tilted one or both of their flippers, reflecting sunlight off the white skin on the underside to disorient fish, the researchers say.

This behavior isn’t just a fluke, the scientists think. Although they observed the behavior in only a few whales feeding near salmon hatcheries (SN: 7/11/17), Kosma speculates that other humpbacks also use their flippers in similar ways when feeding.