Baleen whales are in the suborder Mysticeti. They differ from toothed whales in a number of ways. All mysticetes have two nostrils or blowholes, while toothed whales (odontocetes) have only one blowhole. Mysticetes have a symmetrical skull, while most odontocetes have assymetrical skulls. Most toothed whales have a specialized echolocation system that is lacking in baleen whales. Female mysticetes are usually larger than their male counterparts, but other than that, there is no sexual dimorphism, while there is often marked sexual dimorphism in odontocete species. The most obvious difference between these two suborders, though, is that instead of teeth, mysticetes have baleen made from keratin, the same substance that comprises hair and fingernails. Stiff plates of baleen grow down from the gum of the upper jaws, and depending on the species, the baleen may be black, gray, creamy yellow, white, or a mixture of these colors. The outer edge of each plate is smooth, and the inner edge is frayed. The frayed inner edges intertwine to form a mat, allowing whales to filter feed and trap zooplankton and small fish in their baleen. Like hair and fingernails, baleen continues to grow at its base and wear along the edges.
All baleen whales are carnivorous, and most eat zooplankton or small schooling fish. Most mysticetes employ one of two different systems for feeding, and some species use both systems, depending on the situation and prey density. These systems can be described as “skimming” and “gulping.” Skimming is when a whale swims open-mouthed through a food supply, while gulping, as its name implies, is achieved when a whale swims through a food swarm and gulps large amounts of water and food by extending the ventral grooves in its throat to greatly enlarge the size of its mouth, depressing its tongue, and opening its lower jaw to a nearly 90 degree angle from the body axis. After engulfing the prey, the whale closes its mouth and forces the excess water out through the baleen. It then uses its tongue to transfer the prey to its gullet, and from there, it passes into the stomach. Gray whales, which are mainly bottom feeders, have their own unique style of feeding. Most baleen whales feed for only four months during the summer, and they must consume enough food during this time to sustain them for the rest of the year. It has been calculated that a baleen whale consumes 4% of its body weight per day during the summer feeding season.
Baleen whales are some of the largest animals on earth. In fact, blue whales are the largest animals to have ever inhabited the planet. The buoyancy of water supports a whale’s body, allowing it to grow to a greater size than it could if it lived on land. This large size has several advantages. The decreased surface to body-volume ratio helps a whale conserve heat. The large body size also makes a whale safer from predators, and it allows a whale to eat large quantities of food when food is available and then store this energy in the form of blubber that can be broken down for energy during periods of fasting.
The general body shape of most baleen whales is cylindrical, tapering at the ends. This shape is energy-efficient for swimming and creates less drag. A whale’s skin is smooth and has no oil glands or pores. Many species of mysticetes have sparse hairs on the snout, jaws, and chin, but the lack of hair or fur on the body is an adaptation to reduce drag when swimming.
A baleen whale has a small, external ear opening on each side of its head that leads to an auditory canal. The middle and inner ear is similar to that of other mammalian species, but the ears are adapted for hearing under water.
Baleen whales produce low-frequency sounds, mostly below 5000 Hz. These are some of the loudest sounds produced by any animal, and the sounds travel hundreds of kilometers under water. Scientists think these loud sounds may be used for long-range contact, advertising for a mate, greeting, orientation, navigation, or announcing a threat. The sounds consist of very-low frequency moans, grunts, thumps, and knocks and higher frequency chirps, cries, whistles, and songs.
Some baleen whales can swim as fast as 20 mph (32 kph). They swim by using powerful up-and-down strokes with their tails to push their streamlined bodies through the water. While some mysticetes can dive to depths over 1000 ft (355 m), most species feed at relatively shallow depths. A whale holds its breath when under water, and when it surfaces, it opens its blowholes and blasts a loud exhalation. The whale then quickly inhales and closes its blowholes before diving. Most baleen whales surface and breathe several times before diving. The spout of water that is often the first visual clue of a whale’s presence, does not come from the whale’s lungs. As with other mammals, a whale’s lungs do not tolerate water. Instead, the water spout is produced from water that was on top of the blowhole when the whale exhaled, and the water condenses as the respiratory gases expand in the air. The size and shape of a whale’s “blow” varies from species to species.
Mysticetes can be found in all oceans. They live in polar, tropical and temperate zones. There are three families in the suborder Mysticeti. These are Balaenopteridae, or the Rorqual Whales; Balaenidae, the Right Whales; and Eschrichtidae, the Gray Whale. In my next few blogs, in the family Balaenopteridae, I will cover the blue whale, the fin whale, the sei whale, the Minke whale, and the humpback whale. In the family Eschrichtidae, I will cover the gray whale.
While I see these whales on their summer feeding grounds, I know many of you have watched whales in their winter breeding areas, perhaps in Mexico or Hawaii. Please share your experiences!