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Baleen whales are some of the world's largest animals.
In the ocean, water helps support an animal's body weight, allowing for the potential for greater size than on land.
In general, females are about 5 percent longer than males of the same species.
Baleen whales of the northern hemisphere are usually slightly smaller than their counterparts in the southern hemisphere. And some whale stocks can be larger or smaller than other stocks of the same species. For example, sei whales reach 20 m (65 ft.) in the southern hemisphere, 18.6 m (61 ft.) in the North Pacific, and 17.3 m (57 ft.) in the North Atlantic.
Large size has many adaptive advantages.
Large size decreases an animal's surface-to-body ratio, which helps a mammal retain body heat.
In general, larger animals are safer from predators and are better able to compete for mates.
Large size allows whales to take advantage of seasonal high food productivity. They are able to eat enormous amounts at a time - more calories than they use - and store that energy in the form of blubber.
The largest whale - in fact, the largest animal, living or extinct - is the blue whale.
Average length for Antarctic blue whales is about 25 m (82 ft.) for males and 27 m (89 ft.) for females. (Note: this average does not include measurements taken for a possible "pygmy" subspecies, Balaenoptera musculus brevicauda). Blue whales in the northern hemisphere are slightly smaller.
Record size for a blue whale - for a specimen taken during the whaling years - is 34 m (112 ft.). Another record-size individual weighed 190,000 kg (419,000 lb.).
Pygmy right whales are among the smallest baleen whales. Adult females reach lengths of 6.5 m (21 ft.), and adult males may reach 6.1 m (20 ft.). This species is rarely recorded, so details of its size are poorly documented.
The general body shape of baleen whales is roughly cylindrical but tapering at both ends. This characteristic fusiform shape is quite energy efficient for swimming. Compared to other body shapes, this body shape creates less drag (the opposing force an object generates as it travels through water).
Most baleen whales exhibit skin color variations of black and gray. Some are countershaded: a type of protective coloration in which the dorsal (top) surface is darker than the ventral (underneath) surface. When lighting is from above, the animal appears inconspicuous.
Blue whales are named for a steel blue-gray skin color.
Minke, humpback, bowhead, and fin whales are distinctively colored.
Northern hemisphere minke whales have a band of white across the otherwise black flippers. Individuals in the southern hemisphere may or may not have the flipper band.
Humpback whales are black or gray except for their flippers and the undersides of their flukes, which are white.
Bowhead whales are dark gray to black except for a white chin.
A fin whale's head is asymmetrically colored. The right lower lip is white, and the rest of the head is black or gray. Fin whales also have a grayish white chevron-shaped mark on their backs.
External parasites and algae growing on a whale's skin affect the coloration of some species.
Blue whales sometimes exhibit a yellowish ventral surface, a result of diatom growth. (Diatoms are one-celled algae.)
Barnacles and whale lice give a gray whale its characteristic mottled, light gray color.
Some species, such as gray whales and sei whales, have white or faintly-colored marks or scars. Barnacle growth, shark or killer whale bites, and natural pigmentation differences can create these markings.
Pectoral flippers are a whale's forelimbs. They have all the skeletal elements of the forelimbs of terrestrial mammals, but they’re foreshortened and modified into paddle-shaped appendages. The skeletal elements are rigidly supported by connective tissue: thick cartilage pads lie lengthwise between the bones.
Pectoral flippers are an adaptation for swimming. Whales use their pectoral flippers mainly to steer and, with the help of the flukes, to stop.
Rorquals and gray whales have four digits instead of five: the thumb bones are not present.
Humpback whales have pectoral flippers that are as long as one-third their body length and are a contrasting white color.
The horizontal lobes of the tail of a whale are called flukes. (Each lobe is called a fluke.)
Flukes are flattened pads of tough, fibrous connective tissue, completely without bone or muscle.
Longitudinal muscles of the back and caudal peduncle move the flukes up and down.
In baleen whales, the only traces of hind limbs are two reduced, rod-shaped pelvic bones. These non-functional bones are buried deep in body muscle, not connected to the vertebral column.
Rorquals and the pygmy right whale have a fin on top called a dorsal fin. Like the flukes, the dorsal fin is made of dense, fibrous connective tissue, with no bones.
Dorsal fins are often scarred or marked. Photos of baleen whale dorsal fins can be used for photo-identification.
A humpback whale has a small dorsal fin on top of a hump. The shape varies among humpback whales.
Other rorquals have a backward-curving (falcate) dorsal fin, about two-thirds of the way toward the tail flukes.
Dorsal fins can be about 25 to 60 cm (1-2 ft.) tall, depending on the species.
Right, bowhead, and gray whales have no dorsal fin. Gray whales have a dorsal hump followed by a series of bumps.
Right whales have huge heads - one-fourth to one-third the body length.
In right whales, all seven neck vertebrae are fused, and right whales are incapable of side-to-side head movement.
A right whale's elongated upper jaw bones arch to house extremely long baleen. The lower jaw line is sharply upward-curved in profile.
Encrusting, yellow-white growths on the head, jaws, and blowhole areas of right whales are called callosities. Accumulations of natural markings such as these aid researchers in photo-identification studies.
A rorqual has a broad, flat rostrum and a slightly curved jaw line. Unfused neck vertebrae allow for some flexibility at the head and neck. Some species have ridges on the rostrum and a V- or U-shape to the tip of the snout. A humpback whale has several knobs on its head.
A gray whale has a narrow head with a slight curve to the jaw line. Unfused neck vertebrae allow for some flexibility at the head and neck.
In whales, the nasal openings (nostrils) are at the top of the head.
The nasal opening of a whale is called a blowhole. Baleen whales have two blowholes.
Just as our nostrils lead to an air passage that leads to our trachea and then our lungs, a baleen whale's blowholes lead to an air passage that leads to its trachea and then its lungs.
Each blowhole is covered by a muscular flap. In a relaxed position, the muscular flap provides a water-tight seal.
In the mouth of a baleen whale, stiff plates of keratin grow down from the gums of the upper jaw. These plates are called baleen. They grow in rows on each side of the mouth.
Keratin is a fibrous protein that also composes hair and fingernails. It is strong yet somewhat elastic. Like our hair and fingernails, it grows throughout a whale's lifetime, and the ends continually wear off.
Baleen plates range in color from black to yellow or white, depending on the species.
The outer edge of each plate is smooth. The inner edge is frayed. The frayed inner edges of the plates intertwine to form a mat.
Baleen plates arise in a whale fetus as thickenings of skin on the upper jaw.
Right whales have the longest baleen. Bowhead whales are particularly known for their long baleen plates, which reach lengths of 4 m (13 ft.). Bowhead whales typically have 230 to 360 baleen plates on each side of the upper jaw.
Gray whales have about 130 to 180 baleen plates on each side of the upper jaw. Each plate is about 5 to 25 cm (2-10 in.) long.
In the rorqual family, baleen size ranges from the blue whale's 91-cm (3-ft.) baleen plates to the minke whale's 12 to 20 cm (5 to 8 in.) baleen plates. Blue whales typically have 260 to 400 baleen plates on each side of the upper jaw. Minke whales have about 230 to 360 on each side.
Baleen is an adaptation for filter-feeding.
Parasitic copepods, nematodes, and protozoans can infest a whale's baleen plates.
Baleen whales do not have teeth. They do develop tooth buds during the embryonic stage, but these tooth buds disappear before birth.
Although baleen is not bone tissue, it is sometimes referred to as "whalebone". Baleen whales have also been known as "whalebone whales".
Baleen whales have smooth skin, without oil glands or pores. The epidermis is about 5 to 7 mm (0.2-0.3 in.) thick.
Many species have sparse hairs on the snout, jaws, and chin.
A whale's lack of fur is an adaptation for more efficient swimming: fur or hair creates drag as an animal swims.
A variety of parasites can infest a baleen whale's skin.
Diatoms grow on the skin of some species, including the blue whale. The diatom layer creates an olive-colored film on the skin.
Gray and humpback whales are heavily infested with external parasites. Barnacles and whale "lice" (actually amphipods) attach to skin around the head, blowhole, genital area, and throat grooves. Barnacles feed on plankton in the water. Whale lice feed on whale skin and damaged tissue such as a wound.
Rorqual, gray and pygmy right whales have grooves under the throat that extend to at least the pectoral flippers.
Members of the rorqual family have between 25 and 100 throat grooves, depending on the species.
A gray whale has between two and seven throat grooves.
A pygmy right whale has just two throat grooves.
Right whales do not have throat grooves.
Throat grooves are folds of skin and blubber that expand during feeding, greatly increasing the volume that the whale's mouth can hold. The throat grooves fold back into a streamlined shape when a whale isn’t feeding.