Whale

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Baleen Whales

Baleen whales are named for the long, horny plates of baleen, also known as whalebone, that are attached to the roof of the mouth. Each plate is a thin, triangular sheet with smooth sides made from a strong, elastic protein called keratin, the material that also makes up human hair and fingernails. The outer edge of the plate is straight, while the inner edge and tip are frayed into long, hairlike bristles that serve as a filter to trap minute marine life from seawater.

Some baleen whales feed by skimming—that is, they swim through schools of fish or krill with their mouths open and lower jaw dropped clear of the baleen plates. Other species feed by gulping a single mouthful of food at a time. However they gather food, after sweeping up prey, baleen whales shut their mouths and force water out between the baleen plates. The baleen fringe prevents the small organisms from escaping.

There are three types of baleen whales: rorquals, gray whales, and right whales.

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Rorquals

Rorquals comprise the blue, fin, humpback, Bryde’s, sei, and minke whales. These whales are characterized by pleated throat grooves found on their undersides that extend from the throat to the flippers. While eating, these throat grooves expand, enabling the whale to swallow up to 70 metric tons of water. Rorquals typically have narrow, streamlined bodies and they are the fastest swimming baleen whales—the sei whale, for instance, can swim more than 40 km/h (25 mph) over short distances.

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The blue whale is the largest living animal on Earth, some reaching a length of more than 24 m (80 ft) and a weight of 150 metric tons. As its name suggests, the blue whale is blue-gray in color. The underside is lighter than the rest of the body and often has a yellowish tinge caused by a film of yellow algae that may grow on it. The blue whale makes the loudest sound of any animal—over 150 decibels. This sound, which is louder than the noise of a jet aircraft taking off, can travel over thousands of kilometers underwater. Blue whales have been protected from commercial hunting since 1966, but they remain rare. They are most commonly observed in the northeast Pacific and northwest Atlantic oceans.

The fin whale is the second largest animal after the blue whale. It can grow to 24 m (78 ft) in length and weigh up to 70 metric tons. The fin whale has a gray back and white undersides; the white area extends up along the right side of the lower jaw but not the left. Fin whales are most common in the Southern Hemisphere, while smaller populations inhabit the North Atlantic and North Pacific.

The humpback whale averages about 12 m (40 ft) in length and 30 metric tons in weight. It is black with varying amounts of white on the sides and belly. The humpback’s long flippers may be one-third the length of its stocky body. Groups of several humpback whales have been observed cooperating to trap schools of small fish. The humpbacks corral fish inside a cylindrical column of bubbles released through the whales’ blowholes. Each whale then takes its turn swimming inside the bubble curtain and rising to the surface with its mouth open, trapping many of the fish in its baleen net.

Bryde’s (pronounced “broodahs”) whale is named for a 19th-century Norwegian consul to South Africa named Johan Bryde who built the first whaling stations in South Africa. Bryde’s whales are the only baleen whales that spend their entire lives in warm or tropical waters, preferably those with a temperature above 20°C (68°F). They can be found in both inshore and offshore waters of South Africa, Japan, Sri Lanka, Fiji, and western Australia. Bryde’s whales have a pale gray, slender body that grows up to 14 m (46 ft) in length and weighs up to 24 metric tons. Whale watchers often look for three longitudinal ridges on top of the head to identify this species, which can often be mistaken for the sei whale.

Sei (pronounced “say”) whales are usually about 14 m (46 ft) long and weigh less than 20 metric tons. They are dark blue-gray or black with some white on the undersides. Sei whales are the only baleen whales that feed both by skimming and gulping. They live throughout oceans of the world and generally travel alone but sometimes gather in large loose schools.

The minke whale is one of the smallest of the rorqual whales, growing up to 10 m (33 ft) in length and 10 metric tons in weight. Minke whales are gray-blue, with white bands across the flippers. They have a pointed head that appears V-shaped when viewed from above. Found in waters around the world, minke whales seem to prefer inshore waters.

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Gray Whales

Gray whales are slate-colored and measure up to 15 m (49 ft) in length. Unlike other whales that feed in open water, gray whales are slow swimmers that stay near shallow waters where they can feed from the ocean bottom. They feed primarily on amphipods, a type of small crustacean that lives in mud. Gray whales have the shortest, stiffest baleen fibers of all whales. They approach the ocean bottom sideways, sucking material containing food into the side of their mouth, then forcing water and mud out through the coarse baleen on the other side.

Gray whales live along the coast of North America from the Arctic Ocean to Baja California, Mexico. They migrate annually between summer feeding grounds in the Bering Sea and winter calving and breeding lagoons on the Pacific Coast of Baja, a round trip of some 19,000 km (12,000 mi). A second gray whale population once existed along the coasts of Korea and Japan but was virtually exterminated by commercial hunting early in the 20th century. A few individual gray whales still occasionally appear in these western Pacific waters.

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Right Whales

Scientists recognize three types of right whales: northern, southern, and bowhead, also known as the Greenland right whale. Right whales were so named by early whalers, who considered them the “right” whale to hunt because they swam slowly at 5 to 10 km/h (3 to 6 mph), floated in the water when dead, and were excellent sources of valuable oil and baleen. Right whales are thick-bodied and lack a dorsal fin. They may reach 18 m (59 ft) in length and weigh up to 70 metric tons. They have a callus-like, horny growth, called the bonnet, on top of the head. Right whales have long, thin streamers of baleen for catching small prey. They swim slowly forward with open mouths continuously straining primarily krill, but also copepods and other small organisms from the water.

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Origin of Whales

Whales most likely evolved from four-legged land animals that foraged for food or hunted for fish along ocean shorelines. The ancestors of whales gradually became more dependent on the ocean for food, passing through an amphibian stage before evolving into fully aquatic animals. Recent work with whale fossils indicates that the anklebones of whale ancestors resembled those of artiodactyls, the group of even-toed hoofed mammals that includes pigs, deer, antelopes, and hippopotamuses. Molecular studies comparing the genetic makeup of modern whales to that of other animals indicates that the hippopotamus is the whale’s closest genetic match. Based on these studies, scientists now generally agree that whales are most closely related to artiodactyls.

The fossil record of whales spans over 50 million years to ancestors such as Pakicetus that lived around the mouths of rivers in what is now Pakistan. Pakicetus was a four-legged, land animal that measured about 2.5 m (about 8 ft) in length. The whale fossil Rodhocetus was discovered in 1993. Dating from about 46.5 million years ago, this fossil came from fully marine sediments. Its legs were smaller than those of Pakicetus and its hind feet were turned into webbed paddles. Rodhocetus was clumsy on land, perhaps like modern sea lions. It probably swam using an up-and-down flexing of the body to power its finlike feet in the manner of otters. Unlike modern whales, it had nostrils instead of a blowhole. Rodhocetus also had a powerful tail, although scientists do not know whether this early whale had begun to evolve tail flukes.

A fossil whale known as Basilosaurus dates from 42 million years ago and represents the stage of whale evolution in which the hind legs are very small but still visible. The adult Basilosaurus reached lengths of 15 m (50 ft), but its hind limbs resembled short sticks only 0.5 m (1.6 ft) long. Although all of the pelvic bones, leg bones, kneecaps, feet, and toe bones were present, these legs could not have been used to support such a large animal on land. Modern whales, which first appeared in the fossil record 5 million to 10 million years ago, have no visible hind limbs, although some whale species still have tiny pelvic and leg bones embedded in muscle near the spine.