Blue whales, the largest animals known to have ever lived on Earth, can reach lengths of up to 100 feet and weigh as much as 200 tons. Despite their immense size, their diet is surprisingly specific, focusing on some of the ocean’s smallest creatures.
The Primary Diet of Blue Whales
Blue whales primarily consume krill, small, shrimp-like crustaceans measuring between one and six centimeters long. These tiny animals congregate in massive swarms, sometimes containing over 30,000 individuals. Krill form a fundamental part of the marine food web, consuming phytoplankton and zooplankton, and serving as a food source for numerous larger marine animals.
The blue whale’s diet consists almost exclusively of krill, making them highly specialized feeders. This diet is supported by krill’s abundance and high caloric density, providing the necessary energy for these immense creatures. While the Northern Indian Ocean subspecies may feed predominantly on sergestid shrimp, krill remains the overwhelming food source for most blue whale populations globally. This reliance on a single prey type means blue whales must efficiently locate and consume massive quantities of these small crustaceans.
Filter Feeding: How Blue Whales Eat
Blue whales, as baleen whales, employ a unique feeding strategy called filter feeding. Instead of teeth, they possess baleen plates, comb-like keratin structures hanging from their upper jaw. These plates function as a sieve, allowing water to pass through while retaining food particles.
The primary feeding method is lunge feeding. A blue whale accelerates towards a dense aggregation of krill with its mouth wide open, engulfing an enormous volume of water and prey. Their throat features an expandable, pleated structure that can balloon outward to accommodate this massive intake, potentially engulfing up to 220 metric tons of water at once.
After engulfing water and krill, the whale contracts its throat muscles and uses its large tongue to push water out through the baleen plates. The baleen acts as an efficient strainer, trapping krill inside the whale’s mouth while expelling the water. This highly effective mechanism allows blue whales to capture vast quantities of their small prey with each mouthful.
Massive Appetites and Feeding Grounds
To sustain their enormous body mass, blue whales have substantial appetites. An average-sized blue whale consumes approximately 4 tons of krill daily. During peak feeding seasons, they may eat up to 35,000 pounds of krill per day, representing about 10% of their body weight. This immense consumption meets the high energy demands for activities such as long migrations, maintaining body temperature, and reproduction.
Blue whales undertake extensive migrations, traveling between summer feeding grounds in colder, nutrient-rich waters and warmer tropical breeding areas. These feeding grounds are characterized by highly concentrated krill populations. For instance, blue whales in the Southern Ocean primarily feed on Antarctic krill, and along the U.S. West Coast, they feed off California.
Whales strategically locate these dense patches of krill, as it is important to capture sufficient food in each lunge to justify the energy expenditure of feeding. They optimize their feeding behavior by targeting areas with high krill density, particularly during summer months when krill are most abundant. This efficient foraging in rich feeding grounds supports their survival and the accumulation of energy reserves.