How Whale Sharks Work

Whale Shark Feeding

A large female whale shark swims back for a second helping.
HSW 2008

We know whale sharks are long. Common sense will tell you that they're also heavy. There aren't scales large enough to weigh these beasts, but researchers estimate that larger whale sharks can weigh up to 60 tons (54,400 kilograms). It's hard to believe that a fish can grow this large without eating other large fish. But the whale shark feeds mostly on microscopic and small prey. Its favorite meal is plankton -- the tiny plants and animals that drift throughout the ocean. Occasionally, the whale shark will feed on some small crustaceans, squid and larger plants, but its diet is largely built on some of the smallest ocean creatures.

So how does a 50-foot fish survive by eating microscopic plankton? By eating a lot of it! The trick to getting enough of the small stuff lies in a feature unique to the whale shark. Most filter feeders rely on moving slowly through the water, moving their heads back and forth, to let plankton flow into their mouth and through the gills. The whale shark is more like a vacuum cleaner -- it actually sucks the water into its mouth. This allows it to pull in a lot more plankton than other filter feeders.


Once the whale shark draws in a big gulp of plankton-rich ocean water, it closes its mouth and expels the water through a set of large gills. The gills act like strainers, filtering out the water while keeping solid organisms smaller than about 2 centimeters in diameter. Researchers believe that when larger bits of ocean life get stuck in its gills, the whale shark coughs to clear these filters.

With eyes that are set far back on its head, the whale shark doesn't rely much on vision to find the most plentiful feeding ground. Researchers believe that it uses its sense of smell to locate the most protein-rich waters -- its nostrils are conveniently located near the top of its wide mouth. These creatures like to feed in the evenings near the ocean surface where krill and shrimp are abundant.

Swim ahead to the next page to learn about more about the whale shark and eco-tourism.