Adaptations

Walrus

Adaptations for an Aquatic Environment

Swimming

  1. Normal swimming speed for walruses is about 7 kph (4.3 mph). They are capable of short bursts of up to 35 kph (21.7 mph).
  2. Most propulsion comes from alternate strokes of the hind flippers. Foreflippers also work with the hind flippers for maneuvering.

Diving

  1. Walruses generally breathe at the surface for about one minute after every five to eight minutes of subsurface activity. They can stay submerged for as long as 10 minutes.
  2. Walruses can stay submerged for as long as 10 minutes.

  3. A walrus's bottom-dwelling prey usually inhabit waters no more than about 80 m (262 ft.) deep: a walrus generally dives no deeper than this. Deeper dives, however, have been documented. When the stomach contents of one individual were examined, researchers concluded that the walrus dove to at least 91 m (299 ft.). Another observation confirmed a dive of 113 m (371 ft.) and submersion time of 25 minutes.
  4. All marine mammals have special physiological adaptations for diving. These adaptations enable a walrus to conserve oxygen while it is below water.
    • The heart rate slows during a dive.
    • When diving, blood is shunted away from tissues tolerant of low oxygen levels toward organs where oxygen is needed, such as the heart and brain.
    • The muscle of walruses has a high content of the oxygen-binding protein myoglobin, which transports and stores oxygen.
    • Pharyngeal muscles prevent water from entering the trachea when a walrus opens its mouth below water.

Respiration

  1. A walrus breathes through its nostrils and through its mouth.

Thermoregulation

  1. Heat loss in water is 27 times faster than in air.
  2. A walrus's core body temperature is about 36.6°C (97.9°F). There is a heat gradient throughout the blubber to the skin. The skin stays about 1° to 3°C (1.8° - 5.4°F) warmer than the water.
  3. From about -20° to 15°C (-4° - 59°F) a walrus's metabolism doesn't change, and the temperature doesn't appear to affect the walrus's behavior.
  4. Walruses can withstand even cooler temperatures; they have been observed at -35°C (-31°F).
  5. In cold water, blood is shunted inward as blood vessels in the skin constrict, reducing heat loss to the environment. The skin appears pale, almost white.
  6. When warm, blood vessels in the skin dilate (expand), releasing heat into the environment. The skin appears pink.
  7. When air temperatures rise above 15°C (59°F), walruses often stay in the water to stay cool.
  8. Walruses deposit most of their body fat into a thick layer of blubber - a layer of fat reinforced by fibrous connective tissue that lies just below the skin of most marine mammals. This blubber layer insulates the walrus and streamlines its body. It also functions as an energy reserve. Blubber may be up to 10 cm (3.9 in.) thick. During the winter, blubber may account for one third of a walrus's total body mass.
  9. Walruses have a thick layer of blubber
    that slows heat loss in the water.

  10. Walruses seek out physical contact with other walruses. This helps walruses retain body heat rather than lose it to the external environment. Physical contact is also indicative of their gregarious nature.