Purpose of Porpoises' Porpoising

As porpoises swim near the ocean surface, they are often seen to jump completely out of the water. The behavior is called porpoising. This leaping into the air has been suggested to be a playful antic, but it has a benefit that goes beyond merely having fun. For the porpoise it is a matter of conserving energy as it swims.

Porpoises and dolphins--there is no sharp distinction between the two, except that porpoises are smaller and lack the characteristic beak nose of dolphins--are high-speed swimmers able to move at sustained speeds near 20 mph. To achieve such speed, these mammals must swim at least five or ten feet below the ocean surface. If they try to swim nearer the surface, the passage of their bodies creates waves on the surface, a process which consumes considerable energy. Thus, the porpoise or dolphin will tire quickly if ;i swims very close to the surface for long periods.

Being mammals, porpoises and dolphins must breathe air, hence they must surface at frequent intervals. By experience, they have learned that high-speed swimming and the necessary breathing that accompanies it is best accomplished by swimming well below the surface and then leaping through the highly resistive surface region as quickly as possible. They shoot up out of the water and breathe before falling back through the surface layer to a depth where there is less resistance to their passage. Thus, a porpoise's porpoising has a real purpose.

Porpoises and dolphins also have discovered that they can surf by riding the bow wave of a ship or by riding in storm waves. They cleverly locate their bodies in just the right position in the wave to enable them to move at the speed of the wave with no effort whatsoever.