Whales, the largest animals on Earth, primarily consume some of the ocean’s smallest organisms: krill. This feeding strategy allows these massive marine mammals to thrive in diverse ocean environments. Their ability to sustain themselves on tiny prey involves the unique characteristics of krill, specialized whale feeding adaptations, and immense energetic demands that drive their foraging behaviors.
The Abundant and Nutritious Krill
Krill are small, shrimp-like crustaceans, typically growing to about 6 centimeters (2.4 inches) in length and weighing up to 2 grams. These organisms form a foundational component of marine food webs, particularly in polar waters like the Southern Ocean. Antarctic krill, for instance, can congregate in immense swarms, sometimes reaching densities of 10,000 to 30,000 individuals per cubic meter.
This abundance makes krill an ideal food source for large filter feeders. Krill are also highly nutritious, rich in protein and fats, providing a concentrated energy source for whales. Their high nutritional value and tendency to form dense aggregations allow whales to consume vast quantities of food efficiently, meeting their substantial dietary needs.
How Whales Efficiently Consume Krill
Baleen whales, or mysticetes, possess specialized adaptations that allow them to feed on krill with remarkable efficiency. Instead of teeth, these whales have baleen plates, made of keratin, that hang from their upper jaws. These plates act as a sieve, enabling whales to filter tiny prey from large volumes of water.
Different baleen whale species employ various filter-feeding strategies. Rorqual whales, such as blue, fin, and humpback whales, are “gulp feeders.” They accelerate rapidly into dense patches of krill, opening their mouths to engulf massive amounts of water and prey. Their throat pleats expand significantly, allowing them to take in a volume of water heavier than their own body. The whale then pushes water out through the baleen plates, trapping the krill inside to be swallowed.
Other species, like right whales and sei whales, are “skim feeders.” They swim slowly with open mouths through plankton-rich water, continuously filtering prey. Gray whales are unique bottom feeders, stirring up sediment to filter invertebrates, though their diet can also include krill.
The Energetic Demands of Giant Whales
The immense body size of whales, coupled with their active lifestyles, necessitates a substantial and consistent intake of energy. Maintaining their massive bodies requires considerable metabolic resources. Whales undertake long migrations, often traveling thousands of kilometers between feeding grounds in polar regions and breeding grounds in warmer waters. During these migrations, and particularly while breeding and raising young, many baleen whales fast and rely heavily on stored energy reserves.
To meet these colossal metabolic needs, whales consume vast quantities of high-energy food. A blue whale, for example, can consume between 10 and 20 tons of krill daily during its feeding season, equating to 20 to 50 million calories. Fin whales can eat up to 2,000 kilograms (4,400 pounds) of krill per day. Female whales, especially when pregnant or lactating, face even higher energetic demands, with pregnancy requirements spiking in the final trimester. The ability of krill to form dense, calorie-rich swarms, combined with the whales’ efficient feeding mechanisms, makes this tiny prey perfectly suited to fuel the largest animals on the planet.