What is the inventive hunting technique of humpback whales?

A group of whales swims in a shrinking circle blowing bubbles below a school of prey. Forage fish show a strong fear of bubbles and can be easily contained within a bubble curtain. The shrinking ring of bubbles encircles the school and confines it in an ever-smaller cylinder. The whales, then suddenly swim upward through the "net", mouths agape, swallowing thousands of fish in one gulp.