A. Swimming.
1. Harbor seals swim with all four flippers: their hind flippers propel them forward, and their foreflippers help them steer.
2. Harbor seals can swim forward and upside-down. They rarely swim backward.
3. Harbor seals can swim up to 19 kph (12 mph), but they generally cruise at slower speeds.
B. Diving.
1. Harbor seals can dive to depths of 90 m (295 ft.). They probably don't routinely dive this deep, however, since most of their food is found in shallow waters.
2. Adult harbor seals can stay submerged for 15 to 28 minutes, but dives usually last only three to ten minutes. A two-day-old harbor seal pup can stay submerged for up to two minutes.
3. All marine mammals have special physiological adaptations for diving. These adaptations enable a harbor seal to conserve oxygen while it is under water.
a. Harbor seals, like other marine mammals, have a slower heart rate while diving. The heart rate slows from 75 to 120 beats per minute to only four to six beats per minute. When a seal surfaces after a long dive, it experiences an accelerated heart rate for a short time.
b. When diving, blood is shunted away from tissues that are tolerant of low oxygen levels to the heart, lungs, and brain, where oxygen is needed.
c. A harbor seal has a greater volume of blood than a land mammal of the same size; therefore, it can retain more oxygen.
d. The muscle of harbor seals also has a high content of the oxygen-binding protein myoglobin (about 10 times as much as humans). Myoglobin stores oxygen and helps prevent muscle oxygen deficiency.
4. Before a deep dive, a harbor seal exhales to reduce the amount of air in its lungs. Oxygen is stored in the blood and muscle tissues, rather than in the lungs.
C. Respiration.
Like most other marine mammals, a harbor seal's typical respiration cycle is a short
exhalation, a short inhalation, and a longer breath-holding (apnea) period. 
D. Sleep.
Harbor seals sleep on land or in the water. In the water they sleep at the surface and often assume a posture known as bottling - their entire bodies remain submerged with just their heads exposed. This enables them to breathe when necessary.
E. Thermoregulation.
1. A harbor seal's core temperature is about 37.8°C (100°F). There is a heat gradient throughout the blubber from the body core to the skin. The skin remains about one degree (C) warmer than the surrounding water.
2. Harbor seals have a metabolic rate somewhat higher than land mammals of the same size. This helps keep them warm by generating body heat.
3. A thick layer of blubber insulates the harbor seal, reducing heat loss. The blubber of a northern Pacific harbor seal during winter may account for 27% to 30% of its total body mass. Blubber also streamlines the body and functions as an energy reserve from which the harbor seal can draw energy during periods of fasting. A harbor seal's hair provides no insulation.
4.In cold water, blood is shunted inward as blood vessels in the skin constrict, reducing heat loss to the environment.
5. When hauled out on land, blood vessels in the skin dilate, allowing heat to be released to the environment.
6. To prevent heat from escaping through the extremities, seals hold them close to the body.
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