Aquatic Life

Breathing

Bottle-nose dolphins breathe through their blowhole, which is a specialized single nostril, located at the top of their head. A dolphin may empty and refill its lungs in less than a fifth of a second. As the dolphin breathes the air leaves the blowhole at speeds of over 100 mph. Complex nerve endings around the blowhole sense pressure changes so the dolphin knows exactly when the blowholeis in or nearing air and can be opened. Water in a dolphin's blowhole will actually drown it so powerful muscles close the blowhole as it dives under the water again.

Although dolphins may take a breath of air on the average of 2 to 3 per minute, they can hold their breath for periods in excess of 10 minutes. Dolphins open its blowhole and begins to exhale just before reaching the surface of the water. At the surface, the dolphin quickly inhales and relaxes the muscular flap to close it.

As the dolphin exhales, seawater that has collected around the blowhole is carried up with the respiratory gases. Seawater and the water vapor condensing in the respiratory gases as they expand in the cooler air form the visible blow of a dolphin. During each respiration a dolphin exchanges 80 percent or more of its lung air. This is much more efficient than humans, who exchange only about 17 percent of their with each breath. Exhaling and inhaling takes about 0.3 seconds.

Sleeping

To sleep, a bottle-nose dolphin must shut down only half of its brain, as its breathing is under voluntary control. Dolphins take short catnaps, floating just below the surface, then slowly rising to breathe. Often dolphins are very active during nighttime, for some this is their main feeding time.

A dolphin's behavior when sleeping or resting depends on the circumstances and possibly on individual preferences. They can either:

	Swim slowly and surface every now and then for a breath.
	Rest at the surface with their blowhole exposed.
	Rest on the bottom (in shallow water) and rise to the surface every now and then to breathe.

Generally, female bottle-nose dolphins lie on the water's surface with their blowholes exposed to the air; male dolphins sleep just below the surface and rise to breathe periodically as a reflex action.

Swimming and Diving

"It is the dolphin's birthright to swim in a straight line in the ocean as far as it's heart desires". -Ric O'Barry

The bottle-nose dolphin's skin is completely smooth allowing the dolphin to move easily through the water, and also reduce heat loss. Their bodies are very streamlined so they may swin at high speeds through the water. Their pectoral flippers are used to steer them through the water. Dolphin "friends" may swim along face to face touching fiippers. Dolphins that appear to be closely bonded may swim in synchrony, twisting, turning, and swimming in perfect harmony together.

The dolphin's fast cruising speed, a travelling speed they can maintain for quite a while, is about 6 to 7 knots. When they move faster, they will start jumping clear of the water (porpoising). They are actually saving energy by jumping. It is possible that dolphins can reach speeds of over 15 knots during very short bursts (like in preparation for a high jump), but they can't maintain that speed.

Dolphins are capable of diving more than 1,000 feet below sea level and able to leap to great heights. They may leap to avoid predators or to show how powerful they are to females at mating time. Noisy splashing jumps may also be used to herd fish. Dolphins can stay submerged for up to 15 minutes.

Generally dolphins do not need to dive very deep to catch food. Most dolphins regularly dive to depths of 10 to 150 ft. It is possible for a dive to last eight to ten minutes. All marine mammals have special physiological adaptations used during a dive. These adaptations enable a dolphin to conserve oxygen while it is under water, have a slower heartbeat, blood is shunted away from tissues tolerant of low oxygen levels toward the heart, lungs, and brain, where oxygen is needed.
(Dolphins--The Oracles of the Sea)