Food Preferences and Resources
In general, baleen whales feed low on the food chain, primarily eating zooplankton and small fishes, which they encounter in large swarms or schools.
Right whales eat zooplankton (animal plankton). Their finely fringed baleen is able to strain from the water copepods (a type of small crustacean) and other small zooplankton. Krill (a family of small, shrimplike crustaceans) and copepods are major components of a right whale's diet.
Rorquals generally eat larger prey than do right whales. Depending on species, they eat a variety small crustaceans, squids, and small schooling fishes.
Blue whales eat mostly krill.
Fin whales eat krill, copepods, squids, and variety of small schooling fishes.
Humpback whales, Bryde's whales, and minke whales prey mostly on krill and small schooling fishes. Minke whales in the northern hemisphere prey mostly on small schooling fishes; those in the southern hemisphere prey mostly on krill.
Sei whales eat copepods, krill and amphipods (another type of small crustacean). In the North Pacific and North Atlantic Oceans they also eat squids and small schooling fishes
Gray whales eat mainly invertebrates that live in bottom sediments, mostly amphipods and probably marine worms.
It's likely that some whales' diets depend on food availability.
Food Intake
Most baleen whales spend about four to six months in the summer feeding intensively in high-latitude, productive waters. They spend the next six to eight months traveling and breeding.
Scientists estimate that large baleen whales eat about 4% of their body weight each day during the feeding season. Food intake during the feeding season exceeds daily requirements, and excess energy is stored as fat, much of it in the blubber.
A blue whale eats up to 3,600 kg (8,000 lbs.) of krill each day for about 120 days. It is estimated to take 1,000 kg (2,200 lbs.) of food to fill a blue whale’s stomach.
Gray whales eat about 150,000 kg (340,000 lbs.) of food during a 130 to 140 day feeding period--a daily average intake of about 1,089 kg (2,400 lbs.). It is estimated to take 300 kg (660 lbs.) of food to fill a gray whale's stomach.
Gray whales gain about 16% to 30% of their total body weight during a feeding season.
Throughout the traveling and breeding season, baleen whales eat much less or not at all. Blubber gained during the feeding season sustains the whale during the winter months.
A baleen whale's thick blubber layer stores fat; it is an energy reserve that is necessary during the traveling and breeding seasons.
Winter daily feeding rate is only about 0.4% of body weight.
Blubber makes up 27% of a blue whale's body weight, 23% of a fin whale, 21% of a sei whale, 29% of a gray whale, and 36% to 45% of a right whale.
Method of Collecting and Eating Food
A right whale "grazes" by swimming slowly through swarms of small zooplankton (animal plankton) with its mouth open. At the surface this has been termed "skim-feeding", but right whales also feed under water.
- Water--and zooplankton--enter a right whale's mouth through a gap in the front baleen plates. Zooplankton is caught in the finely fringed baleen mat; water flows through the baleen and out the sides of the mouth.
- With long baleen plates and a huge mouth, right whales are adapted for straining immense amounts of food.
- Right whales usually feed singly, but a group of whales may swim and feed in a V-formation.
Rorqual whales feed by gulping enormous mouthfuls of prey and water. As its mouth fills, a rorqual's throat grooves expand and its mouth cavity balloons outward. Then the whale brings its jaws together and contracts the throat grooves, forcing water out.
- Prey such as krill and small fishes are caught in the baleen mat as water is forced through the baleen and out the sides of the mouth.
- Rorquals may feed at the surface or deeper in the water.
- Some rorquals have been observed sweeping or flicking prey swarms with their the tail flukes toward mouth area.
Humpback whales have been observed blowing "bubble nets" to help them feed. The whale dives down, then swims up in a spiral while releasing bubbles of air from its blowholes. The bubbles float up in a column, keeping prey inside the column. The whale lunges up through the center of the column with its mouth open. Observers have seen several humpback whales lunge-feeding up through a "bubble net", one at a time.
Sei whales have also been observed skim-feeding as right whales do.
Gray whales feed mostly along the ocean bottom. A gray whale rolls on its side and sucks in water, mud, and bottom-dwelling invertebrates, which are abundant in ocean sediments.
- Prey such as amphipods and marine worms is caught in a gray whale's short, coarse baleen mat. Water and mud flow through the baleen and back out.
- Scientists have observed large excavated areas on the ocean bottom in gray whale feeding grounds and have also observed surfacing gray whales trailing streams of mud.
- Curiously, most gray whales appear to be "right-handed". They roll onto the right side when feeding. Others favor the left side. This is apparent by examining gray whale baleen, which is shorter and shows more wear on one side than the other.
- During migration, gray whales may occasionally feed in the water column on swimming prey.
A baleen whale probably uses its huge tongue for moving food trapped inside the baleen, for squeezing water out of the mouth, and for swallowing.
