Adaptations

Baleen Whales

Adaptations

Swimming

  1. A baleen whale swims with up-and-down strokes of its powerful tail flukes. Muscles in the upper and lower regions of the caudal peduncle (tail stalk) provide power.
  2. Rorquals are more streamlined than other baleen whale families, and they swim fastest of baleen whales. The fastest can reach probably approach speeds of 32 kph (20 mph).
  3. Other species travel at slower speeds. Gray whales migrate at about 10 to 11 kph (6-7 mph).
  4. The thick layer of blubber under the skin of a whale results in a streamlined, fusiform body, making a whale energy-efficient for swimming.

Diving

  1. Many species of baleen whales feed in relatively shallow areas of the continental shelf. Most are not known for diving regularly to great depths.
    • Gray whales make shallow dives of 15 to 50 m (50-165 ft.), but may dive for food as deep as 120 m (390 ft.) in polar feeding grounds.
    • Humpback whales dive to at least 148 m (485 ft), and fin whales dive to a maximum of about 355 m (1,165 ft.).
  2. All marine mammals have special physiological adaptations during a dive. These adaptations enable a baleen whale to conserve oxygen while underwater.
    • Baleen whales, like other mammals, have a slower heart rate while diving.
    • When diving, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, lungs, and brain, where oxygen is needed most.
    • Certain protein molecules - hemoglobin and myoglobin - store oxygen in body tissues. Hemoglobin occurs in red blood cells. Myoglobin occurs in muscle tissue. The muscle of baleen whales has twice the myoglobin concentration of the muscle of land mammals.

Respiration

  1. Baleen whales breathe through two blowholes on top of the head. A baleen whale holds its breath under water and surfaces to breathe.
    • As it surfaces, the whale opens its blowholes and explosively exhales.
    • After exhaling, the whale quickly inhales, then closes the blowholes before diving.
    • For a gray whale, each exhalation/inhalation takes about two seconds.
  2. Baleen whales typically breathe several times at the surface before submerging again for several minutes. The number of respirations depends on the whale's activity level. For example, right whales often stay under water for 5 to 15 minutes, then surface and blow five to ten times at 3 to 15 second intervals before diving again.
  3. The visible spout of water that rises from a baleen whale's blowhole is not coming from the lungs, which (like ours) do not tolerate water.
    • Water that is on top of the blowhole when the powerful exhale begins is forced up with the exhaled respiratory gases.
    • Especially in cool air, a mist may form; it is water vapor condensing as the respiratory gases expand in the open air.
  4. Many baleen whale species can often be identified by the size and shape of the "blow".
    • Right whales have a low, bushy blow.
    • A blue whale's blow may reach 9 m (30 ft.) in the air.
    • A gray whale's blow looks heart-shaped when viewed from directly behind or in front of the whale.
    • Minke whales sometimes have no visible blow.

Thermoregulation

  1. Like all mammals, whales are warm-blooded. A baleen whale’s core body temperature is about 36.6˚ to 37.2˚C (98-99˚F) - about the same as that of a human. Living in the sea poses a particular challenge to marine mammals, because heat loss occurs about 27 times faster in water than in air at the same temperature.
  2. The large size of a baleen whale helps minimize heat loss.
    • In general, as an animal increases in size, its surface area decreases relative to volume. A whale's fusiform body shape and reduced limb size further decrease this surface-to-volume ratio.
    • A low surface-to-volume ratio helps an animal retain body heat: the large body core produces metabolic heat. Only through the relatively smaller surface area exposed to the external environment (the skin) is that heat lost.
  3. A thick layer of blubber just under a whale's skin helps insulates a whale from heat loss. There is a heat gradient from the body core, through the blubber, to the skin.
    • Blubber tissue is composed of fat cells and fibrous connective tissue.
    • The blubber layer can reach a thickness of 50 cm (20 in.) on a bowhead whale.
  4. A baleen whale's circulatory system adjusts to conserve or dissipate body heat and maintain body temperature.
    • Some arteries of the flippers, flukes, and dorsal fin are surrounded by veins. Thus, some heat from the blood traveling through arteries is transferred to venous blood rather than the environment. This phenomenon is called countercurrent heat exchange.
    • When a baleen whale dives, circulation decreases at the skin, shunting blood to the insulated body core.
    • During prolonged exercise or in warm water a whale may need to dissipate body heat. In this case, circulation increases near the surface of the flippers, flukes, and dorsal fin. Excess heat is shed to the external environment.