What Do Blue Whales Eat? Krill and Lunge Feeding Explained

What kind of krill do blue whales eat?

Krill are small crustaceans that live in the open ocean and gather in dense swarms. There are dozens of species, and blue whales eat whichever kinds are most plentiful where they feed:

• Southern Ocean: Antarctic krill (Euphausia superba), which grows to about 6 cm (2.4 in) and weighs up to 2 g (0.07 oz).
• California: mainly Thysanoessa spinifera, plus North Pacific krill (Euphausia pacifica).
• North Atlantic: northern krill (Meganyctiphanes norvegica) and Thysanoessa species.
• Southern Australia: pygmy blue whales feed on the krill Nyctiphanes australis.

There is one notable exception. Blue whales in the northern Indian Ocean feed mostly on small sergestid shrimp, diving deeper and for longer than blue whales elsewhere. Small fish and copepods are occasionally swallowed with the krill, but they are a minor part of the diet.

How does lunge feeding work?

Blue whales are rorquals, the group of baleen whales that feed by lunging. A lunge happens in a few seconds:

1. The whale finds a dense swarm of krill and speeds up toward it.
2. It drops its lower jaw open, to an angle of up to about 80 degrees.
3. The grooved, elastic skin of its throat, the ventral pleats, balloons outward as water and krill rush in. A single gulp can hold a mass of water and prey roughly as large as the whale itself.
4. The whale closes its mouth, then squeezes with its throat and pushes with its tongue to force the water out through the baleen.
5. The krill stay trapped inside and are swallowed.

Lunging is hard work. Opening the mouth at speed acts like a parachute, and the whale nearly stops with each gulp. Tagged blue whales sometimes roll sideways or turn upside down during a lunge, which may help them line up with the thickest part of a swarm.

How does baleen work?

Instead of teeth, a blue whale has several hundred black baleen plates hanging in rows from its upper jaw, each less than 1 m (3.3 ft) long. Baleen is made of keratin, the same tough protein as human fingernails and hair. The inner edge of each plate frays into a mat of bristles, and together the plates form a sieve that lets seawater out but holds krill in.

All baleen whales feed this way to some degree, but they use it in different styles. Gray whales sift mud on the seafloor, and right whales skim slowly through the water with their mouths open. To compare the groups, see What are baleen whales?

How much does a blue whale eat in a day?

Nobody can watch a blue whale eat for a whole day, so intake is estimated from feeding behavior and the density of krill. Older estimates suggested that an adult eats about 3–4 tonnes of krill a day, and NOAA notes that some of the biggest individuals may eat up to 6 tons.

More recent work suggests the true figure may be higher. A 2021 study led by Matthew Savoca combined data from suction-cup tags with sonar measurements of krill swarms. It estimated that an eastern North Pacific blue whale eats about 16 tonnes of krill a day during the feeding season, with a plausible range of roughly 10–20 tonnes.

Earlier work by Jeremy Goldbogen and colleagues, published in 2011, showed why blue whales seek out the densest swarms. When krill are tightly packed, a single mouthful can supply up to about 240 times the energy the whale spent on that lunge. In thin swarms, lunging barely pays, so whales skip them.

Where and when do blue whales feed?

Most blue whales feed in cold, productive waters in summer and fall, such as the Southern Ocean around Antarctica, the coast of California and the Gulf of St. Lawrence in Canada. Krill gather where currents bring nutrients up from the deep, often along continental shelf edges and submarine canyons.

Krill move up toward the surface at night and sink deeper by day, and blue whales follow them. Off California, feeding dives average about 200 m (660 ft) deep and last around 10 minutes. Between dives, the whales surface to breathe several times before going down again. For record dives by other species, see How deep can whales dive?

Do blue whales stop eating during migration?

Many blue whales eat little while migrating and during the winter breeding season, living on energy stored as blubber during months of heavy feeding. Pregnant females have to build especially large reserves, since they must later produce rich milk for a calf that gains about 90 kg (200 lb) a day.

The pattern is not universal. Some blue whales feed in their winter areas, such as the Gulf of California and the Costa Rica Dome in the eastern Pacific, where krill can also be abundant. Others remain in productive waters most of the year.

How can tiny krill feed the largest animal on Earth?

It seems strange that the biggest animal eats some of the smallest prey, but the logic is simple. Krill feed on microscopic plant plankton, so they sit near the base of the food chain, where energy is most plentiful. Antarctic krill alone are thought to have a total weight of hundreds of millions of tonnes, making them one of the most abundant animals on the planet.

By swallowing whole swarms at once, a blue whale harvests thousands of animals in every gulp instead of chasing single prey. This efficient way of feeding is what allows baleen whales to reach such enormous sizes, as explored in How big is a blue whale?

Blue whales also give something back. Their nutrient-rich feces fertilize surface waters, helping the plankton that krill depend on.