http://www.sciencemag.org/news/2019/12/how-humpback-whales-sneak-thousands-unsuspecting-fish

For many ocean creatures, there’s safety in numbers. A school of small, fast-moving fish can confuse and distract larger, lumbering predators such as sea lions, which are generally out for a single snack. But that strategy doesn’t work as well when the fish are faced with a heftier threat such as a humpback whale that can engulf nearly two-thirds of a school in one gulp.

To find out how these whales are able to catch speedy fish by surprise, researchers snuck up on individual anchovies in the lab with animations of fake “predators” (really just appropriately sized dots) to see what would send the fish fleeing. As it turns out, humpback whale–size predators are so enormous that the fish don’t even register them as threats as they approached from afar, the team reports today in the Proceedings of the National Academy of Sciences.