Click here for the updated InfoBook - Walrus.
Adaptations for an Aquatic Environment
A. 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.
B. Diving.
1. Walruses generally breathe at the surface for about one minute after every five to eight minutes of subsurface activity. Walruses can remain submerged for as long as ten minutes.
2. A walrus' benthic prey usually inhabits waters no more than about 80 m (263 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 at least 91 m (299 ft.). Another observation confirmed a dive of 113 m (371 ft.) and a submersion time of 25 minutes.
3. All marine mammals have special physiological adaptations for diving. These adaptations enable a walrus to conserve oxygen while it is below water.
a. Walruses, like other mammals, slow their heartbeat while diving.
b. 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.
c. The muscle of walruses has a high content of the oxygen-binding protein myoglobin. Myoglobin transports and stores oxygen in muscle tissue.
4. Pharyngeal muscles prevent water from entering the trachea when the walrus opens its
mouth below water.
C. Respiration.
A walrus breathes through its nostrils and through its mouth.
D. Thermoregulation.
1. Heat loss in water is 27 times faster than in air at the same temperature.
2. A walrus' core body temperature is about 36.6 degree C (97.9 degree F). There is a heat gradient throughout the blubber to the skin. A walrus' skin stays about 1 to 3 degree C (1.8 to 5.4 degree F) warmer than the water.
3. From about -20 to +15 degree C (-4 to +59 degree F) a walrus' metabolism doesn't change, and the temperature doesn't appear to affect the walrus' behavior.
4. Walruses can withstand even cooler temperatures; they have been observed at -35 degree C (-31 degree 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), losing heat to the environment. The skin appears pink.
7. When air temperatures rise above about 15 degree C (59 degree F), walruses often stay in the water to stay cool.
8. Walruses deposit most of their body fat into a thick layer of blubber
that lies just underneath the skin. 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' total
body mass.
A Walrus' blubber layer may be as thick as 10
cm (3.9 in.).
For an activity appropriate for grades 4-8, click here.
9. Walruses seek out physical contact with other walruses. This helps walruses retain their body heat rather than lose it to the external environment. Physical contact is also indicative of their gregarious nature.
