What Are Baleen Whales? How Whales Without Teeth Eat

What is baleen made of?

Baleen is made of keratin, the same protein that forms human hair and fingernails, strengthened with minerals. It grows as a row of thin, flat plates on each side of the upper jaw, hanging down like the slats of a vertical blind. The outer edge of each plate is smooth, while the inner edge frays into a mat of hair-like bristles. Together, these mats form the filter.

Baleen grows throughout the whale’s life, while the bristles on the inside wear down, much like fingernails. The number, length and color of the plates vary by species:

• Humpback whale: about 540–800 black plates in total.
• Gray whale: about 130–180 short, cream-colored plates on each side.
• Bowhead whale: the longest baleen of any whale, about 4 m (13 ft).
• Fin whale: plates that are pale at the front of the right jaw only, part of its lopsided coloring.

Before plastics and spring steel, baleen was used for corset stays, umbrella ribs and buggy whips, and whalers called it “whalebone”, although it is not bone at all.

How do baleen whales feed?

All baleen whales are filter feeders, but they use three main methods.

Lunge feeding (gulping). Rorquals, such as the blue whale, fin whale and humpback whale, have long pleats running along the throat. They charge into a dense swarm of krill or school of fish, open their jaws wide and let the throat balloon out, sometimes taking in a volume of water larger than their own body. They then push the water out through the baleen with the tongue. See What do blue whales eat? for how it works in the biggest whale of all, and What is bubble-net feeding? for the humpback’s special trick.

Skim feeding. Right whales and the bowhead whale have huge, arched heads and very long, fine baleen. They swim slowly with their mouths open through patches of tiny copepods, filtering continuously. Sei whales skim as well as lunge.

Bottom feeding. The gray whale rolls onto its side on the seafloor and sucks up mud, then pushes it out through its short, stiff baleen, keeping small crustaceans called amphipods. Gray whales often favor one side, so the baleen on that side wears down more.

How many kinds of baleen whales are there?

Scientists recognize about 15 or 16 living species, grouped into four families. The exact number depends on whether Bryde’s whale and Eden’s whale are treated as one species or two.

Some scientists place the gray whale among the rorquals. Two species were named only recently: Omura’s whale in 2003 and Rice’s whale of the Gulf of Mexico in 2021. Rice’s whale is one of the most endangered whales on Earth.

Baleen whales vs toothed whales

Whales are split into two living groups. Baleen whales form the Mysticeti, while toothed whales, the Odontoceti, include more than 70 species of dolphins, porpoises, beaked whales, sperm whales, belugas and narwhals.

The orca, despite being called a killer whale, is a toothed whale and the largest member of the dolphin family, as explained in Is an orca a whale or a dolphin?

Why are baleen whales so big?

Filter feeding lets baleen whales harvest huge amounts of tiny prey in a short time, as long as the prey is packed into dense swarms. A 2021 study using tags and sonar estimated that baleen whales eat about three times more than earlier estimates suggested; a blue whale may eat around 16 tonnes of krill a day during the feeding season.

Fossils show that giant size is fairly recent. Before about 4.5 million years ago, few baleen whales were longer than about 10 m (33 ft). Gigantism appears to have evolved within the last few million years, as ocean changes during the ice ages concentrated food in rich, seasonal patches. Being huge let whales store energy, travel long distances between feeding areas and exploit those patches efficiently.

Where did baleen come from?

The ancestors of baleen whales had teeth. Some of the earliest known members of the group, living more than 30 million years ago, still had a full set of teeth. Later species such as Aetiocetus may have had both teeth and early baleen, and over time the teeth were lost. Modern baleen whale embryos still begin to form tooth buds, which are reabsorbed before birth, a trace of this ancient history.