What do blue whales eat?

The Blue Whale Diet

Blue whales are the largest animals on Earth, yet they feed on one of the ocean’s smallest creatures: krill. These tiny shrimp-like crustaceans, typically only 1 to 2 inches (2-5 cm) long, make up nearly 100 percent of the blue whale’s diet.

What Is Krill?

Krill are small crustaceans belonging to the order Euphausiacea. The species most commonly eaten by blue whales include:

• Antarctic krill (Euphausia superba): The primary prey for Southern Hemisphere blue whales
• North Pacific krill (Euphausia pacifica and Thysanoessa spinifera): Important for blue whales in the eastern Pacific
• Northern krill (Meganyctiphanes norvegica): Consumed by North Atlantic populations

Krill form enormous swarms — sometimes stretching for miles — that provide the concentrated food source blue whales need to sustain their massive bodies.

How Much Do Blue Whales Eat?

During the summer feeding season in cold, productive polar waters, an adult blue whale consumes approximately:

• 4 tons (3,600 kg) of krill per day
• 40 million individual krill per day
• Up to 500 kg of krill in a single feeding lunge

This intense feeding builds up thick layers of energy-rich blubber that sustain the whale during winter months, when it migrates to warmer waters and eats little or nothing.

How Blue Whales Feed

Blue whales are lunge feeders. The process works in stages:

1. Detection: The whale locates a dense krill patch, often at depths of 300 feet (100 m) or more
2. Acceleration: It accelerates toward the krill swarm at high speed
3. Engulfment: The whale opens its enormous mouth and engulfs a massive volume of water and krill. The ventral throat grooves expand like an accordion, allowing the mouth to hold up to 90 tonnes of water
4. Filtration: The whale pushes the water out through its baleen plates — flexible, comb-like structures that trap the krill while allowing water to drain
5. Swallowing: The trapped krill is swallowed

Despite their size, blue whales are remarkably efficient feeders. Each lunge takes enormous energy, so they target only the densest krill patches to maximize their caloric return.

Seasonal Feeding Patterns

Blue whales follow a dramatic annual feeding cycle:

• Summer (feeding season): Blue whales spend months in cold, nutrient-rich waters near the poles, eating intensively. They may gain 50 or more tons during this period.
• Winter (breeding season): Blue whales migrate to warmer tropical waters to breed and give birth. During this time, they eat very little and rely on their fat reserves, potentially losing 25-30% of their body weight.

This feast-or-famine cycle is common among baleen whales and drives their long-distance migrations between polar feeding grounds and tropical breeding areas.

Do Blue Whales Eat Anything Besides Krill?

While krill constitutes the overwhelming majority of the blue whale diet, they occasionally consume small fish and copepods (tiny crustaceans). However, these alternative prey items make up a negligible portion of their overall food intake. For a comparison with other whale species’ diets, see what do whales eat.