Baleen whales (Mysticeti) are a group of marine mammals distinguished from toothed whales (Odontoceti) by their unique feeding apparatus. Unlike toothed whales that hunt individual prey, mysticetes are filter feeders that consume vast quantities of smaller organisms. Their mouths contain plates of baleen, which are long, keratinous structures that hang from the upper jaw in place of teeth. These bristly plates form an intricate sieve designed to strain minute prey, such as krill and zooplankton, from the water column.
The Four Major Families
The baleen whales are divided into four distinct families, each representing a unique evolutionary path. The largest and most diverse group is the Balaenopteridae, commonly known as the rorquals, which includes the Blue, Fin, Humpback, and Minke whales. Rorquals are characterized by their sleek, streamlined bodies and a series of longitudinal ventral grooves running from the jaw to the chest. These grooves allow the throat and mouth to expand dramatically during the rapid process of engulfing water and prey.
The second family, Balaenidae, comprises the Right whales and the Bowhead whale, which are recognizable by their massive, robust bodies and disproportionately large heads, which can make up nearly 40% of their total length. These whales lack the dorsal fin and throat grooves found on rorquals. Their highly arched upper jaw accommodates the longest baleen plates of any whale species. Right whales are noted for the rough, barnacle-encrusted patches of skin on their heads known as callosities.
The family Eschrichtiidae contains only a single living species, the Gray whale, which exhibits a mottled gray appearance due to the presence of whale lice and barnacles on its skin. Gray whales are further distinguished by having a dorsal hump followed by a series of knuckles or bumps along their back instead of a true dorsal fin. The fourth family, Neobalaenidae, is represented solely by the Pygmy Right whale, a species restricted to the Southern Hemisphere. This whale is the smallest of the baleen whales and, unlike its larger Right whale relatives, possesses a small, curved dorsal fin and a more slender body.
Diverse Feeding Mechanisms
The anatomical differences among the families correlate directly with three specialized methods of filter feeding. Rorquals use a highly energetic method called lunge feeding, which involves accelerating rapidly to engulf a massive volume of water and prey. The ventral grooves expand, stretching the throat cavity to hold a volume of water that can exceed the whale’s own body weight. Specialized sensory organs allow the lower jaw to rotate outward almost 90 degrees during this high-speed gulp.
After engulfing the water and prey, the rorqual uses its powerful throat and tongue muscles to force the water back out through the baleen plates, trapping the concentrated food inside. This intermittent ram feeding strategy is energetically costly but allows them to exploit dense patches of krill and small schooling fish. In contrast, Right whales and Bowhead whales employ a continuous method known as skim feeding, where they swim slowly near the surface or at depth with their mouths held open. The extremely long, fine-bristled baleen plates filter out small crustaceans as the water continuously flows through the mouth and out the sides.
The Gray whale utilizes a unique strategy known as bottom suction or benthic feeding, often performed by rolling onto its side near the seafloor. The whale then uses its tongue to create a powerful suction force, vacuuming up mouthfuls of sediment and the small invertebrates that live within it. The coarser, shorter baleen plates then strain the invertebrates from the expelled mud and water, making the Gray whale one of the few baleen whales that feeds almost exclusively on organisms dwelling on the ocean floor.
Comparing Size and Global Movements
Baleen whales showcase an impressive range in physical size. The Blue whale, a rorqual, holds the title of the largest animal on Earth, reaching lengths of up to 98 feet and weights approaching 200 metric tons. The Pygmy Right whale measures only about 20 to 21 feet long, making it the smallest of the living baleen whales. The physical dimensions of these animals are directly tied to their need to process vast amounts of water and maintain body heat in cold environments.
The lives of many baleen whales are defined by extreme, seasonal global movements between feeding and breeding grounds. Species like the Humpback and Gray whales undertake some of the longest migrations of any mammal, traveling thousands of miles each year. Humpback whales often migrate 5,000 miles or more between their summer feeding areas in cold, polar waters and their winter breeding and calving grounds in warmer, tropical latitudes. The Gray whale’s annual round-trip journey between the Arctic feeding grounds and the shallow, protected lagoons of Baja California, Mexico, can cover up to 12,000 miles, making it the longest-known migration route for any mammal.