1. Swimming speed and duration are closely tied:  high-speed swimming probably lasts only seconds while low-speed swimming may last for long periods of time.

2. Killer whales are among the fastest swimming marine mammals.  They can swim at speeds up to 48.4 kph (30 mph), making them perhaps the second fastest marine mammal next to the Commerson's dolphin, which reaches swimming speeds up to 56 kph (35 mph).   Killer whales generally cruise at much slower speeds, however, usually from 3.2 to 9.7 kph (2 - 6 mph).

3. Killer whales are very agile and maneuverable in the water.

4. When swimming near the surface, killer whales generally stay below water for 30 seconds or less.

1. When they dive, killer whales usually go to depths of about 30.5 to 61 m (100 - 200 ft.).  Killer whales generally do not dive deep, although the deepest dive known under experimental conditions was 274.3 m (900 ft.).

2. When diving, killer whales may surface about every four to five minutes.  At the surface they generally take two to five breaths at five to ten second intervals before another dive.  They make approximately three to five short dives, each lasting 10 to 35 seconds.  These are followed by longer dives lasting about one to four minutes.

3. Dives up to 10 minutes and longer have been seen, with the longest dive observed in the ocean lasting 12 minutes.  Under experimental conditions, killer whales have made dives lasting as long as 15 minutes.

4. All marine mammals have special physiological adaptations when they dive.   These adaptations enable a killer whale to conserve oxygen while under water.

a. Killer whales, like other marine mammals, have a slower heart rate while diving.   A killer whale's heart rate can slow from 60 beats to 30 beats per minute while diving.

b. When diving, blood is shunted away from tissues tolerant of low oxygen levels (like the extremities) and channeled toward the heart, lungs, and brain, where more oxygen is needed.

c. Marine mammals have a higher concentration of the oxygen-binding protein myoglobin in the muscles.  Myoglobin stores oxygen and helps prevent muscle oxygen deficiency.   These combined adaptations allow a killer whale to conserve oxygen during a dive.

5. A serious threat to human divers is decompression sickness or "the bends".

a. When humans dive with air tanks, decompression sickness can result from changes in the state of nitrogen molecules (the largest component of air) inside the body following changes in pressure.  This occurs because nitrogen becomes more soluble as pressure increases.  As a human diver ascends, dissolved nitrogen returns to its gaseous state and tiny bubbles may form inside the capillaries (the tiniest blood vessels).

b. Because it breathes at the surface, a killer whale is not inhaling air under pressure.  And as a killer whale dives deeply, its flexible lungs collapse, forcing air into the windpipe and nasal ducts, where internal body surfaces cannot absorb nitrogen.

c. Nevertheless, after repeated dives, the nitrogen concentration in a killer whale's muscle tissue may increase to levels high enough to cause decompression sickness in humans.  Diving experiments with bottlenose dolphins suggest that cetaceans can tolerate higher nitrogen concentrations than humans can.  How this works is unclear but may be related to differences in body chemistry.

1. Heat loss in water is about 27 times faster than in air at the same temperature.

2. Despite this rapid heat loss, killer whales are able to maintain a high body temperature that ranges from 36.4 C (97.5°F) to 38 C (100.4°F).

3. Killer whales have several adaptations to help them stay warm even in frigid water:

a. A killer whale has a thick layer of body fat, called blubber, that lies underneath its skin.  This blubber layer, from 7.6 to 10 cm (3 - 4 in.) thick, insulates the whale and streamlines its body.

b. The killer whale's fusiform body shape and reduced limb size, in comparison to land mammals, decreases the amount of surface area exposed to the external environment.   Blubber also functions as an energy reserve.

c. In general, cetaceans have a higher metabolic rate than land mammals of similar size.  This increased metabolism generates a great deal of body heat.

d. Mammals lose body heat when they exhale.  Because they breathe less frequently than land mammals, killer whales conserve a considerable amount of heat.

4. A killer whale's circulatory system adjusts to conserve or dissipate body heat and maintain body temperature.