The Blue Whale (Balaenoptera musculus) is the largest animal ever known to have lived on Earth. These magnificent marine mammals are up to 100 feet long and upwards of 200 tons. Their tongues alone can weigh as much as an elephant. Their hearts, as much as an automobile.
Blue whales feed almost exclusively on krill, though they also take small numbers of copepods. The species of this zooplankton eaten by blue whales varies from ocean to ocean. An adult blue whale can eat up to 40 million krill in a day. The whales always feed in the areas with the highest concentration of krill, sometimes eating up to 3,600 kilograms of krill in a single day.
Their feeding habits are seasonal. Blue whales gorge on krill in the rich waters of the Antarctic before migrating to their breeding grounds in the warmer, less-rich waters nearer the equator. The blue whale can take in up to 90 times as much energy as it expands, allowing it to build up considerable energy reserves. Because krill move, blue whales typically feed at depths of more than 100 meters during the day and only surface-feed at night. Dive times are typically 10 minutes when feeding, though dives of up to 21 minutes are possible.
The whale feeds by lunging forward at groups of krill, taking the animals and a large quantity of water into its mouth. The water is then squeezed out through the baleen plates by pressure from the ventral pouch and tongue. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed.
Blue whales look true blue underwater, but on the surface, their coloring is more a blue-gray. Their underbellies take on a yellowish hue from the millions of microorganisms that take up residence in their skin. The blue whale has a broad, flat head and a long, tapered body that ends in wide, triangular flukes.
Aggressive hunting in the 1900s by whalers seeking whale oil drove them to the brink of extinction. Between 1900 and the mid-1960s, some 360,000 blue whales were slaughtered. They finally came under protection with the 1966 International Whaling Commission, but they’ve managed only a minor recovery since then. Blue whales have few predators but are known to fall victim to attacks by sharks and killer whales, and many are injured or die each year from impacts with large ships.