Dolphins at Sea

Masters of the ocean

Dolphins have evolved into masters of the ocean by developing hairless, smooth-skinned and streamlined bodies perfectly suited to moving through the relatively dense medium of water. Dolphins can swim with ease at speeds of up to 55 kph (34 mph). The speed and agility of dolphins has been recognised ever since humans first ventured out on to the sea, but clearer appreciation of their ability only developed as a result of research carried out in the late 1940's.

Swimming

Although dolphins possess the low-drag, tear-drop shape of a typical fish, they swim quite differently. Most fish swim by flexing the body sinuously and sweeping the tail fin through the water from side to side. Dolphins, (and whales), swim by thrusting their flukes up and down. The flukes are themselves shaped like the wing of an aircraft. Forward motion is generated largely on each upstroke, the power stroke, which drives the water from the upper surface of the flukes to their lower surface. On the downward, or recovery, stroke this process continues while the natural buoyancy of the head causes the front of the body to rise. Two blocks of powerful muscles on either side of the spine drive the flukes, but the whole of the body also flexes as part of the swimming action. The skin of a dolphin has texture rather like rubber. Not only does this present a smooth surface over which the water can flow easily, but some scientists also believe that a dolphin can actually flex its skin while swimming to subtly alter its body profile and minimise drag still further.

Dolphins can stay submerged for up to 15 minutes whilst diving to depth of up to 300 metres (1000 feet). At this depth their lungs are almost totally compressed.

The distance a dolphin travels depends very much on its food supply. The optimum swimming speed (the speed at which a dolphin spends a minimum of energy and hence can maintain for a long time) is about 8 kph (4 mph). Dolphins sleep about 8 hrs/day which would leave 16 hours for travel. This would mean they could travel up to 128 km/day (80 miles). How much they actually do travel is unknown.

Whilst all dolphins swim slowly at times those coastal dolphins which tend to feed on slower moving prey are rarely able to swim at high speeds. As they rise to breathe they barely disturb the surface water and show relatively little of themselves before disappearing again.

Some dolphins are able to achieve high speeds by leaping out of the water in a series of arcs every time they need to breathe instead of swimming along the surface. In exceptional circumstances they have been known to reach speeds of 40 kph (25 mph). By leaping completely out of the water they are able to reduce turbulence and drag at the water’s surface and maintain speed while using the minimum amount of energy.

Bow-riding

Bow-riding occurs when dolphins swim alongside a boat, riding a pressure wave. this seems to be great fun for them.

Logging

At quieter times they might be seen 'logging', this is when they float on the water's surface. This is a great energy saving, resting position.

Lobtailing

This is sometimes known as tail-slapping, which is just what it describes, a hard smack of the water by a whale's fluke, or tail. One of the reasons this might be done is in order to cause a loud sound to stun or confuse prey. When the other end of the body appears (i.e. the head) for a good look around, then this is known as spyhopping. This is thrilling for dolphin and whale watchers as everybody gets a good look at their face and eyes.

Breaching

This is the most exciting sight to see above the waves and catch on camera. Breaching requires a great deal of power. Sometimes whales breach multiple times in a row. Humpback, Right and Sperm whales are particularly fond of leaping clear of the water in this way. Whales may breach to dislodge parasites or it could be to create a similar effect to lobtailing, to convey messages to other members of their group, or for pleasure of play.

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