Dolphins and gannets blast through a shimmering, pulsing vortex of sardines in these up-close glimpses of an underwater buffet.

The video was taken by biologist Robin Vaughn during her graduate studies at Texas A&M University. She was interested in how dolphins — in this case, dusky dolphins in New Zealand’s Admiralty Bay — approached formations of schooling fish called prey balls.

In a prey ball, tens or hundreds of thousands of fish cluster into a dense swarm, moving as a single entity. “It’s not clear if they’re getting into this shape because dolphins are eating them, to reduce their chances of being eaten. Or it’s possible that dolphins are herding them to be in that shape,” said Vaughn. “Or it could be a combination.”

Floating with an underwater video camera and trying to stay inconspicuous, Vaughn filmed hundreds of feeds between 2005 and 2006, enough to see patterns. Dolphins circled clockwise around prey balls — dolphins appear, like most humans, to favor their right sides — skimming bites off the edges rather than plunging straight in. Often two dolphins would attack at the same time, rather than individually. When prey balls tried to dive, dolphins herded them back up.

Vaughn has since graduated, but the lab of co-author Bernd Würsig, also a Texas A&M biologist, will continue to study how these patterns differ between dolphin species and populations. Their findings will be published in an upcoming issue of Ethology.

Videos: Above, dolphins and gannets feed on what Vaughn said is an average-sized prey ball. Below, dolphins feed on an especially large ball. Courtesy of Robin Vaughn

See Also:

Citation: “Dolphin Bait-Balling Behaviors in Relation to Prey Ball Escape Behaviors.” By Robin L. Vaughn, Elisa Muzi, Jessica L. Richardson, Bernd Würsig. Ethology, September 2011.