Risky Business

Whale sharks are a bit like pop stars: They attract a crowd. Smaller fish swarm around them. That’s probably a better deal for some fish than others. Sometimes, predators can wolf down entire schools of the groupies in a matter of seconds.

Whale sharks are the largest fish on Earth. They can span 25 feet or more. They’re filter feeders—they filter tiny fish and other small organisms from the water as they swim along with their mouths wide open.

The sharks often are accompanied by other fish. That includes a hodge-podge of smaller fish known as baitfish. They’re a few inches long, and there can sometimes be so many of them that they look like a shimmering cloud around a shark.

Biologists have speculated that one reason the baitfish hang out near the whale sharks is protection—predators might keep their distance from the giants. But a recent study in Australia found otherwise.

Scientists analyzed video shot over several years. The pictures showed larger fish gobbling up the baitfish. Most attacks lasted no more than about 20 seconds, with no or few survivors.

That leaves a couple of other explanations for why the smaller fish hang around the sharks. They might get a bit of a free ride—either riding the wave that forms ahead of the shark, or “drafting” behind it like a car following a big truck. Also, the smaller fish eat the same food as the sharks, so the whale sharks might take them to good hunting grounds—the good part of swimming with sharks.