The blue whale, the largest animal on Earth, sustains its immense size by consuming one of the ocean’s smallest creatures: krill, which are tiny, shrimp-like crustaceans. The sheer scale of this mammal, which can weigh up to 150 tons, demands an extraordinary amount of energy, making its specialized diet a biological necessity. To meet its massive caloric needs, the blue whale has evolved a unique feeding strategy centered almost exclusively on these small, abundant crustaceans.
Krill: The Exclusive Fuel Source
Krill provides the dense, high-calorie fuel required to power the blue whale’s enormous body and migratory lifestyle. These small crustaceans are rich in both fat and protein, offering a concentrated source of energy that few other prey items can match. The blue whale’s diet consists of krill for over 99% of its intake, with copepods or small fish only occasionally ingested as bycatch.
Krill form extremely dense swarms containing millions of individuals. These aggregations create a localized, highly concentrated food patch that makes bulk feeding energetically worthwhile. Blue whales are seasonal feeders, consuming the vast majority of their annual calories during a short, intense feeding season. During this time, they can ingest an estimated 4 to 16 metric tons of krill per day.
A Whale of a Mouth: Baleen Filtration Systems
The anatomy of the blue whale’s mouth is specifically adapted to process the massive volumes of water and prey required for its survival. Instead of teeth, the upper jaw is lined with hundreds of specialized structures called baleen plates, which function as a highly efficient sieve. These plates, typically ranging from 260 to 400 on each side, are made of keratin, the same fibrous protein found in human fingernails and hair.
Each baleen plate has a smooth outer edge facing the lip and a fringed inner edge composed of fine bristles. These fringes intertwine to form a dense, fibrous mat inside the mouth, capable of trapping the small krill while allowing seawater to pass through. To accommodate the huge incoming volume of water and krill, the blue whale possesses highly elastic folds of skin and blubber along its throat, known as ventral throat grooves or pleats. These pleats allow the throat pouch to expand dramatically, ballooning out to temporarily hold a mixture of water and prey that can sometimes exceed the whale’s own body weight.
The Energetic Process of Lunge Feeding
The physical act of lunge feeding is a highly specialized and energetically demanding hunting behavior unique to rorqual whales. When a blue whale locates a dense krill swarm, it accelerates rapidly toward the patch, often reaching peak speed just before initiating the engulfment. The whale opens its mouth wide, sometimes to an angle of 90 degrees, in a fraction of a second.
This action instantly creates massive drag, causing the whale to decelerate sharply as its mouth fills with water and prey. The oral cavity expands, enabled by the stretching of the ventral throat grooves, engulfing a volume of water that can be up to 100 metric tons in under ten seconds. Once the mouth is closed, the whale uses its enormous, powerful tongue to force the engulfed water out through the baleen plates. The krill are then filtered onto the dense, bristled mat of the baleen fringes and swallowed. This high-cost strategy is only profitable if the targeted krill patch is dense enough to ensure the energy gained outweighs the significant energy expended during the rapid acceleration and engulfment.