Dolphins

Intelligent marine mammals

All animals except man know that the ultimate of life is to enjoy it" - Samuel Butler 1912.

Today we feature yet another unique marine mammal which is facing serious problems due to us humans. It is the lovable dolphin, a cousin of the famous dolphin

named Flipper in the popular TV series which was telecast sometime ago. Let's check out the lifestyle, habits, and physical features of these cute-faced marine creatures who are known to be very intelligent when compared to most other marine animals,These intelligent mammals are found in our country too. There have been several reports of dolphins being caught in the nets of our fishermen and being injured or killed, eventually.

Dolphins belong to the family Delphinidae, which is the largest and most diverse family of the cetacean order and include 26 living species. Several species of dolphins are found in the Hawaiian waters. However, it is not only in this area that they are found. Dolphins inhabit the oceans worldwide, mostly in the shallower seas of the continental shelves. The family Delphinidae is considered a relatively recent addition to the cetacean family, having evolved more recently than the others of its family. Most species of dolphins are larger than porpoises, with the males usually being larger than the females.

The name is originally from the Ancient Greek word (delphs; "dolphin"), which was related to the Greek word (delphys; "womb"). The name can therefore be interpreted as meaning "a 'fish' with a womb.

Dolphins are extremely social creatures and they depend on their social relations even while hunting as well as in reproduction. Unlike the humpback whales and other species of baleen whales, dolphins live in tightly knit groups - smaller groups are called pods which range between two to forty members, and larger groups called schools or herds. These groups can include more than one species, because each species has its own niche. Spotted and Spinner dolphins are constantly found living in such groups. Researchers believe that this is possible because spotted dolphins usually prey on larger creatures closer to the surface, while the Spinner dolphins tend to feed in deeper waters on smaller prey.

They are carnivores, maintaining a diet of mainly fish and squid.

Dolphins are some of the most intelligent animals, and their playful behaviour and friendliness have made them very popular among humans.

Dolphins are adapted extremely well to the sea. Even though their hind limbs have disappeared, their front limbs have developed into flippers. Their powerful tail is the main instrument for them to move forward. Dolphins possess a distinct beak. Their teeth are conical in shape Dolphins usually breathe through what is called the blowhole on the top of their heads. They can empty their lungs and refill them in one fifth of a second. As they breathe, the air leaves the blowholes at speeds of over 100mph. But how do they know when to open their blowholes, because if they open them in the water, they could die?. Well, as we know by now, all creatures are built with special features needed to help them survive in the habitats they live in. So, dolphins too have such special features and they know exactly when the surface is near so that they could open their blowholes. Water in a dolphin's blowhole will definitely drown it, therefore powerful muscles close the blowhole as soon as it dives under the water after taking in a breath of air.

Its eyes produce a slippery liquid which protects the dolphin from unknown substances as well as the water. Like whales the dolphin can only sleep with one brain resting at a time or else it can drown. Dolphins take short cat-naps, floating just below the surface, and then slowly rising to breathe, because breathing is a voluntary procedure for the cetaceans. Often dolphins are very active during night time, and for some, this is their main feeding time.

The skin is completely smooth unlike that of most other mammals, and this allows the dolphin to move faster in the water.

Their bodies are built in a way they could swim at high speeds through the water, and an example of this is their ears. Dolphin's ears are barely noticeable marked only by a small hole just behind the eye. In a bottlenose dolphin, the ear is about 5-6 cms behind the eye and only 2-3 mm in diameter.

Because dolphins feed on schools of prey, most species have developed communal and cooperative hunting practices, as searching for food as a group is more efficient than searching individually. The exception to this rule is the river dolphin who usually feeds on individual prey on the river bottom. They are often found living alone or in very small groups.

Most dolphins move in groups that are wider than long. They do this so that they can scan as large an area as possible, using their echo location. The size of the groups may be determined by the number of dolphins able to be sustained by the school of prey.

Dolphins and all species of whale use their exceptional hearing in an extremely sophisticated manner, known as echolocation. This is when the animal emits a variety of split-second "clicks" through its blowhole. The "clicks" are pulses of ultrasonic sound (sounds repeated as rapidly as 800 times/second) produced in a dolphin's nasal passages and are focused in a large, lens-shaped organ in the forehead known as the melon. The melon focuses the sound on to a specific area. When the sound waves bounce back in to the dolphins' path as it hits the object, the dolphins can map its route and find its prey.

Using this amazing skill, a dolphin can create a picture of its surroundings and can determine the size, shape, direction of movement and distance of objects in the water. This allows the dolphin to hunt over a wider range than their limited visibility normally allows.

Most groups of dolphins have strict hierarchical patterns, and there are a few dominant members within the group. Large groups are often mixed in terms of age and gender, but smaller groups are generally one of three types: 1) A nuclear group that includes a single adult male and female; 2) A nursery group, consisting of a number of females and their young; 3) A bachelor group comprised of adult and younger males.

Regardless of the type, all groups of dolphins seem to have well-developed skills in cooperating and working together as a team whether it be for the purpose of finding food, mates or caring for their young.

The maturing period varies with the species of dolphin in question, however typically a calf is born every other year.

Dolphins are able to leap great distances, and the males frequently do this to demonstrate how powerful they are to a female. Research suggests that the average gestation period for a dolphin is round about twelve months. Like the whale, dolphins too give birth to their calf, tail first.

The newborns senses are fully developed and functioning. As soon as it is born, the calf is nosed to the surface by its mother so that it can breathe. The mother will stay with her calf for a period of two years to sometimes even eight, and as in humans, the mother will nurse her baby with milk and care for it till it can fend for itself.

Threats: Thousands of dolphins and small whales throughout the world continue to be hunted for food, oil, fertiliser and other products. The fishermen use boats and large nets to "drive" schools of dolphins into shallow bays and harbours where they are killed, often brutally.

The meat is often sold for human or animal consumption, or made into fertiliser. Japan is believed to be the largest consumer of dolphin.What may turn out to pose the greatest threat to dolphins (and other marine animals for that matter) is our contamination of the marine environment- their home.

Pesticides, PCBs, heavy metals, plastic particles, and other industrial wastes are released into our oceans, bays and rivers in unknown amounts daily.

Many of these pollutants do not break down in the environment, or take a very long time to do so. In addition, many dolphin deaths have been attributed to swallowing man-made objects including balls, nets and pieces of plastic.

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Fact file

* They are known to save humans in distress at sea.

* A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".

* Some types of dolphins must rise to the surface to breathe every 20 to 30 seconds.

* Each dolphin has its own signature whistle to identify itself.

* Five specific species live in fresh water; they are usually named after the river they swim in such as the Amazon, the Yangzi Jiang, or the Ganges.

*Dolphins seems to enjoy playing games with humans; they invent them if you don't.

* Males can whistle to get the attention of females or to warn the group of imminent danger.

* Cetaceans can taste, but have no sense of smell.

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-Salindri PERERA