OCEAN ANIMALS
EPIPELAGIC ZONE
There are also large predators in the epipelagic zone. Tuna feed on squid and fish. They are streamlined and can swim powerfully for long distances.
Marine mammals live in this zone. At first glance, fish and marine mammals look similar but they differ in very important ways. Fish are scaly; marine mammals such as the whale or dolphin are covered with soft skin. Fish breathe through gills; whales have lungs and respire through a blowhole in the top of the head. Fish fins are spiny; whale fins are solid and their flippers are bony. Whales evolved from land animals like the wolf, with long legs for walking. They may have gone through a seal-like stage with short limbs for walking or swimming. Now, they have only front limbs and a long, flexible backbone.
Seals are highly streamlined, with a good deal of body fat which helps to keep them warm, and improves the smoothness of their streamlining. Seals and sea lions can spend days or weeks in the water, feeding at sea, making sea journeys of hundreds or thousands of kilometres, and returning to land to breed.
The largest predators are whales. They are by far the most efficient of all the aquatic animals, hunting and catching all their food in the water. They sleep floating on the surface. Whales, like dolphins, mate in the sea and bear their calves in the water. The baby whale (calf) can swim as soon as it is born. A whale may eat 10.000 kg of plankton at one meal, though the main constituents of a whale's diet are shrimplike krill.
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