DOLPHINS AND PORPOISES

BOTTLENOSE DOLPHIN

Dolphins and porpoises were original land-dwelling mammals. Through a miracle of evolution they changed into an aquatic grace and power of a fish. A whole adaptation took place for location and pursuing their prey in the water. Originally their bodies are constructed on the same principle as ours. However, over 10 million years of continuing evolution and adaptation they changed into a fish. They have a stream like body and ability to propel themselves with their fin-like tails. Their acquired speed and agility even outnumbers their biggest enemy, the shark. Yet, they still have the most characteristics features of their land-based ancestors. They have warm blood, lungs for breathing air and suckle their young.

Their closest relatives are the great whales. The blue whale is the largest animal that has ever lived. The sperm whale with its vast, wax-filled head. The baleen whales which filters tiny planktonic animals from the water through the sieve-like curtain of baleen. The toothed whales which snatches its prey.

PORPOISE

Dolphins and porpoises are simply small toothed whales. Their diet consists mainly of fish and squid. The killer whale or orca is the biggest of the dolphins. Its prey are seals and other dolphins.

The distinction between dolphins and porpoises is that the porpoise has a flat, spade-shaped teeth. The dolphin has conical, peg-like teeth and has a fleshy beak. Other than that they two species are similar.

Quite a few mammals have adapted to be good swimmers. The seals are a perfect example. However, the dolphins and porpoises have changed so much to life in the water that they are helpless now on land.

Their biggest change was in their body shape. It was necessary to streamline their bodies because water is much more tense than air. Therefore, marine animal have to be streamlined to be able to move fast. Dolphins and porpoises changed into mini-torpedoes with no projections. Gone have their ear flaps and their hind limbs, their sexual organs are fully enclosed in their bodies and their fore-limbs changed into hydrofoils to stabilize and steer their bodies. Their tails extended into a broad, stiffened flukes which is powered by their massive back muscle and propels them through the water with such perfect efficiency.

 A FIFE WEEK OLD DOLPHIN EMBRYO.  THE HIND LEGS CAN STILL BE SEEN AS SMALL BUMPB NEAR THE TAIL.  THE PIN IS 2.5CM LONG

DALL'S PORPOISE

Their skin is silky and smooth. Any irregularities on their bodies such as bones or muscles are smoothed out by a thick layer of fat. The fat is also an insulator and protects the body from heat loss because sea water is always cooler than their warm blooded body.

The body of the dolphin is a nature miracle. When the water flows over the animal it will cause turbulence which drags the dolphin due to the alteration of the pressure. The dolphin's skin automatically resists this and develops small transverse ridges. It cancel the development of turbulence. Another incredible point is that the dolphins shed its outer layer of skin. Apparently 12 times a day. It also discharges droplets of oil and it is assumed that shedding skin and oil may increase its speed. The fastest species is the Dall's porpoise and it has a speed of up tp 50km/h for quite a distance.

These spectacular leaps of dolphins have two purposes. One it reduces the drag because air is less resistant than water. The other reason is it can breathe. It breathes out through the blowhole in the top of its head and take rapidly a breath before plunging into the water again.

Dolphins very seldom dive deeply. It only needs half a second above the water to get the required oxygen. If they do dive deep, they absorb more air in their lungs than us and store is in their red blood cells. The dolphins and porpoise have more blood in their body than land mammals of the same size. This enables them to store more oxygen.

Dolphins and porpoises hunt in clear, sunlit waters of the oceans. The important vision comes from an extreme flexible lens. It enables them to see in the air and under water. The beaked species like the bottle nose dolphin has a binocular vision. However, in an experiment, they blindfolded the dolphins and it was noted that they can still perform equally efficient. They using their sensing their surrounding.

Their ears are only small holes behind their eyes but they are most important. Their ears are highly efficient and adapting to the sound travelling under water. It is a true stereo system which enables the animal to know the direction of sound.

Human being's ears are not equipped to that. The sound goes through its head and affects the ears at the same time. Dolphins' and porpoises' ears are in a foam and this isolate it from the skull. The animal notes the time sounds arrive first in one ear and than in the other and from that it determines the direction it came from.

This is necessary because they live in a world of sounds. They use sonar like the bats. They themselves emit continuously short sound signals which then bounce off solid objects and come back as echos. The time between sending and receiving gives the animal the range of object.

The signals are a series of clicks. They are short but very frequent. The clicks seem to come from the blowhole, reflecting off the concave front surface of its skull. This is focused by an acoustic'lens' of fatty tissue above the snout. It is the domed forehead that can be seen on many species. By continuous analyzing the echoes the animals build a complete sound picture of their surroundings which warns them of obstructions or danger.

To work these information out continuously needs a lot of brain cells. The weight of a dolphins' or porpoises' brain is 2kg. The human brain is 1.5kg. It shows that they are intelligent and have a great capacity of learning.

Dolphins and porpoises mostly eat fish and squid. The beaked species with numerous small teeth are mainly fish-eaters. The killer whale, a very large dolphin, eats warm-blooded marine animals such as seals, penguins and other whales. It had been noted that they attack, kill and partially eat blue whales.

Porpoises hunt in small groups of tow to four individuals. The open-sea dolphins travel in herds of 1000 or more. They travel in a broad band with smaller groups within. The smaller group are more consistent and stay together for weeks or months. The large group changes with individuals come and go.

In place where the ocean currents pushes cold but nutrient rich water up from the sea bed and this mixes with the warmer water on the surface, creating plankton growth, there are the biggest prime feeding sites. This attracted great shoals of fish like capelin and anchovy which in turn attracts dolphins.

When dolphins discover these sites they swim round and round in ever decreasing circles. This method will force the fish together and force them to the surface. When they achieved this they snapping them up and swallow them whole.

BRIDLED OR SPOTTED DOLPHIN

In the Pacific, spinner and bridled dolphins hunt together.  When one species feeds the other watches out for predators.  The yellow-fin tuna usual mixes with them and take advantage of the dolphins echolocation skills to find preys.  It is no  loss to the dolphins because there usually is plenty for all of them.  The tuna then repays the hospitality and gives early warning of shark attack.

However, the sharks are not the worst predators but it is man.  The dolphins guide the fishing boats and because of the tuna joining the dolphins they are often in mortal danger.  Firsherman look out for dolphins which swim and leap on the surface.  They lay a purse-seine net around them knowing that the tuna swims underneath.  The bottom of the vast net is drawn together to form a mesh bag.  The fishermen tightening it slowly but surely together.  The dolphins are there in it with the tuna.  When the net is hauled on board the dolphins get crashed by machines.  Previously, it was estimated that 130,000 dolphins died that way in a year. 

More recently, because of the campaigns, the nets were produced with fine mesh panels.  The dolphins can recognize it and leap over it.  Also some divers and boats help the dolphins to escape but there are still a huge number of dolphins being unnecessarily killed by tuna fisheries.  In the drift-net the dolphins have not the chance to disentangle themselves and simply drown..

Dolphins and porpoises are more or less just mating for the recreational purpose.  The male does not help with bringing up the calf which will suckle for up to two years.  It will take solid food several months before it is weaned.  All this time is closely guarded by the mother. 

However. the killer whale consists of one male and several females.  The male will stay with them for life.  They will rear several broods of young.  The family group is called pod and has several sub-adult and juveniles whales of both sexes.  They all hunt together and the ones with more experience and knowledge show the other what to do.

KILLER WHALE

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