Blue whales are the largest animals ever known to have lived on Earth. These magnificent marine mammals rule the oceans at 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 have a long body and generally slender shape. Their mottled blue-gray color appears light blue under water. The mottling pattern is variable and can be used to identify individuals. Blue whales reach these mind-boggling dimensions on a diet composed nearly exclusively of tiny shrimplike animals called krill. During certain times of the year, a single adult blue whale consumes about 4 tons of krill a day.

Blue whale migration patterns are not very well known or understood, but seem to be quite diverse. Some populations undertake long migrations to high-latitude feeding grounds while others, like the population found in Sri Lanka, appear to be resident year-round in habitats that show high productivity throughout the year.