ARI SHAPIRO, HOST:
This next story is about the anchovy and the whale - specifically about why an agile anchovy can't escape from a ponderous whale. NPR science correspondent Joe Palca reports that as with so many things in life, the answer is timing.
JOE PALCA, BYLINE: Whale biologist David Cade, who recently graduated from Stanford University, says there's no question humpback whales enjoy a tasty meal of anchovies, but they're not always successful at getting one.
DAVID CADE: We've noticed that when a humpback whale approaches a fish school, sometimes that whole fish school disperses, and the fish all escape. And sometimes, the whale can catch a lot of those fish. And so we were trying to figure out what's going on. What is the triggering mechanism that makes an anchovy respond to an oncoming threat?
PALCA: To answer that question, Cade brought some anchovies into a lab at the Hopkins Marine Station.
CADE: So what we did is we had some anchovies in a tank. And we would playback basically an oncoming stimulus. It's basically like an expanding dot, like, coming towards your face. And fish would get scared at a certain point.
PALCA: And once scared, the anchovies would head for the hills - or maybe that's not the best metaphor, but you get the point. The thing is, most of the time, humpback whales seem to have a pretty good idea about just when that scary point is. So Cade says when the whales come across a school of anchovies out in the ocean, if they open their mouths and time their last-second lunge at the school just right, they can gobble up a whole mess of anchovies.
CADE: So there's a really narrow window in which the humpback whale can successfully time the mouth opening in order to catch the most fish.
PALCA: Cade reports his findings in the latest issue of the journal PNAS. This ability to eat anchovies and other prey fish instead of just depending on a steady diet of krill might help explain a puzzle about humpbacks.
Ari Friedlander is at the Institute for Marine Science at the University of California, Santa Cruz.
ARI FRIEDLANDER: One of the things that we've noticed in the scientific community is that humpback whales are repopulating around the world at really fast rates. And this is, you know, recovery from commercial whaling 100 years ago.
PALCA: So if you like the fact that humpbacks are making a comeback, thank an anchovy. Joe Palca, NPR News.
(SOUNDBITE OF THOMAS NEWMAN'S "FIELD TRIP") Transcript provided by NPR, Copyright NPR.