Blue whales, the largest animals to ever inhabit this planet, reach up to 100 feet in length and weigh up to 190 tons; females and those in the Southern Hemisphere tend to be the largest. Numbering 350,000 before the age of modern whaling ships, 99% of their population was decimated during the early-mid 1900s. Slowly recovering since the 1970s, blue whales now number somewhere in the range of 8-15,000 individuals, 2/3 of which live in the Southern Hemisphere.
Protected from human hunting, these marine giants now face a dwindling population of krill, their primary food source. Krill are small, shrimp-like crustaceans that live in the open ocean waters, feeding on phytoplankton and often massing in huge schools, containing billions of individuals. In fact, their vast numbers make krill the most abundant (by mass) animal on the planet; 85 species inhabit the Earth's oceans. Nevertheless, krill populations are diminishing, having dropped by 80% over the past 30 years in some parts of the Antarctic. The cause for their demise remains uncertain but warming sea temperatures and a reduction in sea ice are thought to play a role (krill feed on algae that accumulate on the underside of the ice shelfs). In recent decades, man has also been harvesting krill for use as aquaculture feed and for the production of krill oil, a popular health food item. Should krill populatins continue to decline, the welfare of all baleen whales and many species of penguin, seal, fish and sea birds will be threatened.
To support their massive frame, blue whales consume up to 4 tons of krill each day; much of this consumption occurs in the cold polar seas during the summer months, when the perpetual daylight fosters extensive phytoplankton blooms (and thus phenomenal runs of krill). Moving on to Temperate and Tropical seas to give birth and to breed during the winter months, blue whales feast on other krill populations along the way. Impregnated females carry their calf until the next winter and will then nurse it for another 8 months; mature females generally give birth every 2-3 years. Despite the many threats to their welfare, blue whales may live 80 years or more.
