Solitary Seafarer Blue whales have been sighted in all of the Earth's oceans. Although rich feeding areas can attract large numbers of them, these giants most often travel singly or in small groups. © David B. Fleetham / Visuals Unlimited

The blue whale (Balaenoptera musculus) is the largest animal that ever lived. An adult can grow nearly as long as three school buses and weigh over 400,000 pounds—as much as 24 African elephants. Being big has its advantages. Large whales are safe from most predators and their massive bodies retain heat well—a bonus when in chilly ocean waters. But enormous creatures also have to eat enormous quantities. Amazingly, the blue whale maintains its bulk on a diet of mostly shrimplike krill.

Blue whales are difficult to study because they spend so little time at the surface and migrate to remote waters. So as big as these animals are, we still know remarkably little about how they live.

Bottom's Up Blue whales usually feed at depths of 50 to 300 meters (165 to 1,000 feet). When they dive, they use their powerful tail flukes to propel themselves straight down. Increasing water pressure compresses the air in their bodies, eventually making them denser than water. They are then able to descend without additional propulsion. © Tui De Roy/Oxford Scientific Films

Seasonal Menu
In spring and early summer, blue whales migrate from warm tropical waters to colder regions rich with krill. They filter their tiny prey out of the water using comblike baleen.

During its feeding season, a blue whale must capture about 40 million krill a day. That sounds like a daunting task, but blue whales are built for it. They have throat grooves that expand like accordion bellows and long jawbones, which allow the whale to gulp in as much as 17,000 gallons of krill-rich water at a time. The whale then closes its mouth, leaving a fringe of baleen around the opening. Its tongue forces the water out through this natural filter, trapping the krill inside.

Adult blue whales gorge for six to eight months, storing extra energy as blubber. They then return to warmer waters to breed and give birth.

CONSERVATION: Few and Far Between
Twentieth century whalers decimated blue whale populations. They harvested over 350,000 individuals, leaving perhaps as few as 6,000 alive.

Today, a reduced population may be the blue whale's biggest problem. Low population means low density—and less chance for potential mates to meet. It also means a smaller gene pool, which could produce less healthy offspring.

However, one notable success story is unfolding off the West Coast of North America. Blue whale sightings have increased, and scientists are using new satellite tracking methods to study these animals. They hope that what they learn about the whales' migration and breeding grounds can help protect blue whales worldwide.