Aimed at our young people in particular, The Sri Lankan Guardian launches a campaign to help develop awareness of our rich natural assets and the need to protect and conserve them. We will from time to time publish features and reports on nature life which we are confident, will be used in schools as supportive material. Our first feature is based on ocean life and is all about dolphins written by our Consulting Editor, Victor Karunairajan.++++++++++++++++++++++++++++++
Delightful Dolphins
by Victor Karunairajan
(March 05, Toronto, Sri Lanka Guardian) Dolphins like the whales and porpoises are aquatic placental mammals. Though smaller than the whales they are larger than the porpoises and belong to the order Cetacea, fishlike water mammals without external hind limbs but with paddle-like forelimbs.
The earliest known scientific observations on dolphins go back to the time of the Greek philosopher, Aristotle, 384-322 BC. An amazing student of politics, literature, philosophy and biology, he had scientifically observed over five hundred animals and was primarily interested in marine life.
In his written work, Historia Animalium, he described the dolphin as a mammal with lungs and a blowhole, sleeps with its nose above the water and snores while sleeping. He further observed: “No one is ever seen to be supplied with eggs, but directly with an embryo, just as in the case of mankind. Its period of gestation is ten months, and it brings forth its young in the summer.
“The dolphin is provided with milk and suckles its young which accompany it for a considerable period. In fact, the creature is remarkable for the strength of its parental affection.
“The young grow rapidly, being full grown at ten years of age. It lives for many years; some are known to have lived for more than twenty-five and some thirty years. The fact is fishermen nick their tails sometimes and set them adrift again, and by this expedient their ages are ascertained.”
Dr Lyall Watson, an authority on whales has referred to these observations of Aristotle in his extremely fascinating sea guide to the Whales of the World, as an astonishing piece of natural history replete with accurate observations.
Aristotle’s information was acquired as a direct result of observations and experiments with live animals, and in the case of the dolphins, Dr Watson states the Greek philosopher’s account of the Common Dolphin (Delphinus delphis) is so good that there is little that could be added to it even now.
Three centuries later, the Roman writer, Pliny the Elder in his extensive study on natural history published as a 37-volume encyclopaedia, included a whole book on dolphins and their cetacean cousins, the whales. Pliny’s writings were based on material he had drawn from about two thousand ancient books written by almost five hundred scientists, naturalists and writers.
In recent times, the credit for the best works on marine biology, particularly in respect of studies on whales, dolphins and porpoises belong to the Swedish scientist, Carolus Linnaeus (1707-78) and much later, John Hunter a Scottish surgeon, and Edward Gray, a pioneer of cetacean taxonomy.
It was Linnaeus who established the binomial system of biological nomenclature that forms the basis of modern classification of plants and animals. This classification is based on certain characteristics common to each such as structure, embryology and biochemistry.
According to the classification of cetacean species there are three families of dolphins, the Platanistidae, Stenidae, and Elphinidae. The habitats of the five species of the Platanistidae family are spread over in some Asian and South American rivers such as the Ganges, Bramaputra, Indus, Yangtze, Amazon and the Orinoco.
The members of the Stenidae family are the Roughtooth Dolphins, Indo-Pacific Humpback Dolphins, and the Estuarine Dolphins. Their habitats which extend through the tropics, are largely coastal or more precisely, estuarine. The Common Dolphin and the Bottlenose Dolphin, easily the most popular ones are two of the twenty-two known Delphiniadae species.
They are found in the oceanic waters of the tropics and certain northern regions. The Common Dolphin species could be identified as ones that usually swim together in large active schools often churning up a wide area of water.
According to Dr Watson, in any school it is possible to see dolphins rolling up to breathe, leaping out in smooth arcs to re-enter head first, splashing down on their heads and backs, pounding on the water with their chins and flukes, or zigzagging along just beneath the surface. They usually breathe several times each minute, but have been known to dive for as long as five minutes.
“They readily come to bowride, shifting restlessly in the pressure wave to find the best position, often rolling over on their sides to look up at the humans. The speed of the ship seems to present no problems. A group of them were once seen at the bow of a destroyer in the Mediterranean travelling at 64 kph. A school, often with calves travelling in tender, may bowride for twenty minutes or more.”
Scientists have often asked the question as to how the dolphins are able to move so effectively, efficiently and at such speed. Soviet scientists who carried out extensive investigations into this aspect observed that in active swimming, all the dolphin layers of skin interact with the flowing current. They do so in such a way as to result in a reduction of hydrodynamic resistance. This is promoted by highly sensitive receptors that catch the slightest changes of water resistance in any part of the skin surface.
Due to vascular system mobility, the elasticity and other physio-mechanical skin characteristics alter, resulting in turbulence reduction in the onrushing current. The conclusion the scientists have drawn from this observation is that in the dolphins all skin layers interact with each other. The signals about the character of the current trigger the automatic regulation of the mechanical skin properties and as a consequence, the resistance to swimming declines; the higher the speed the lower the resistance becomes.
The practical importance of this study opened up extensive possibilities to work out artificial skins or covers capable of significantly reducing both hydrodynamic resistance and vibrations. These covers may prove useful in the further development of underwater mechanisms for fishermen and seabed explorers with resistance to movement and noise lower than those in the existing models. The world of dolphins has much to offer the humans to study and understand the marine environment better.
In many areas, the Bottlenose Dolphins, known to make much out of bowriding, follow trawlers and shrimp boats feeding on fish stirred up or discarded by the nets. But they can easily hunt on their own. This was well illustrated by an incident observed by Dr Watson in the Black Sea.
A group of Bottlenose Dolphins chased a school of bluefish into a shallow bay and held it there by deploying two of their number to act as sentinels while the rest hung back outside the bay and took turns to feed on them. As a social unit, the Bottlenose Dolphins move around in a group of about twelve to fifteen but there are records of as many as a thousand.
Among the most interesting and clownish of the dolphins, a group of untrained Bottlenose Dolphins in captivity in South Africa were known to regularly mimic fur seals, skate and loggerhead turtles.
In one case, using a seagull feather held in its beak as a scraper, one of the dolphins imitated the actions of a human diver cleaning the side of a glass on underwater portholes, complete with vivid imitation of the sound involved in the cleaning and the breathing of the man through the aqualung, bubbles and all.
“The Bottlenose actually performed this task so effectively that, after just one demonstration, it was never necessary for a diver to do that job again.” Dr Watson has also related another interesting incident, which is perhaps very typical of the dolphins.
In what he calls the “most devastating example of mimicry that has been encountered in any animal,” a young Bottlenose Dolphin seeing a human observer blowing clouds of cigarette smoke in an idle offhand manner outside one of the viewing ports, sought its mother, returned with a mouth full of milk, waited until the smoker was at the window again and then blew the milk out in a cloud against the glass. This action produced precisely the same effect underwater that the smoke had in the air.
There are countless numbers of stories about dolphins safe-navigating sailors through many treacherous waters particularly in and around the regions of Panama: some of them are indeed most touching incredible acts of chivalry.
These examples alone indicate to the humans as to why the world of the dolphins in particular and the cetaceans in general is one that has been around for twenty million years. The human beings have clocked 500,000 years and are already struggling to survive. If the humans will learn from the dolphins they may not only save the cetaceans but in the process ensure their own future too. It is therefore vital that through the thoughtlessness of the humans, the cetaceans should never disappear from the face of the earth.
Delightful Dolphins
by Victor Karunairajan
(March 05, Toronto, Sri Lanka Guardian) Dolphins like the whales and porpoises are aquatic placental mammals. Though smaller than the whales they are larger than the porpoises and belong to the order Cetacea, fishlike water mammals without external hind limbs but with paddle-like forelimbs.
The earliest known scientific observations on dolphins go back to the time of the Greek philosopher, Aristotle, 384-322 BC. An amazing student of politics, literature, philosophy and biology, he had scientifically observed over five hundred animals and was primarily interested in marine life.
In his written work, Historia Animalium, he described the dolphin as a mammal with lungs and a blowhole, sleeps with its nose above the water and snores while sleeping. He further observed: “No one is ever seen to be supplied with eggs, but directly with an embryo, just as in the case of mankind. Its period of gestation is ten months, and it brings forth its young in the summer.
“The dolphin is provided with milk and suckles its young which accompany it for a considerable period. In fact, the creature is remarkable for the strength of its parental affection.
“The young grow rapidly, being full grown at ten years of age. It lives for many years; some are known to have lived for more than twenty-five and some thirty years. The fact is fishermen nick their tails sometimes and set them adrift again, and by this expedient their ages are ascertained.”
Dr Lyall Watson, an authority on whales has referred to these observations of Aristotle in his extremely fascinating sea guide to the Whales of the World, as an astonishing piece of natural history replete with accurate observations.
Aristotle’s information was acquired as a direct result of observations and experiments with live animals, and in the case of the dolphins, Dr Watson states the Greek philosopher’s account of the Common Dolphin (Delphinus delphis) is so good that there is little that could be added to it even now.
Three centuries later, the Roman writer, Pliny the Elder in his extensive study on natural history published as a 37-volume encyclopaedia, included a whole book on dolphins and their cetacean cousins, the whales. Pliny’s writings were based on material he had drawn from about two thousand ancient books written by almost five hundred scientists, naturalists and writers.
In recent times, the credit for the best works on marine biology, particularly in respect of studies on whales, dolphins and porpoises belong to the Swedish scientist, Carolus Linnaeus (1707-78) and much later, John Hunter a Scottish surgeon, and Edward Gray, a pioneer of cetacean taxonomy.
It was Linnaeus who established the binomial system of biological nomenclature that forms the basis of modern classification of plants and animals. This classification is based on certain characteristics common to each such as structure, embryology and biochemistry.
According to the classification of cetacean species there are three families of dolphins, the Platanistidae, Stenidae, and Elphinidae. The habitats of the five species of the Platanistidae family are spread over in some Asian and South American rivers such as the Ganges, Bramaputra, Indus, Yangtze, Amazon and the Orinoco.
The members of the Stenidae family are the Roughtooth Dolphins, Indo-Pacific Humpback Dolphins, and the Estuarine Dolphins. Their habitats which extend through the tropics, are largely coastal or more precisely, estuarine. The Common Dolphin and the Bottlenose Dolphin, easily the most popular ones are two of the twenty-two known Delphiniadae species.
They are found in the oceanic waters of the tropics and certain northern regions. The Common Dolphin species could be identified as ones that usually swim together in large active schools often churning up a wide area of water.
According to Dr Watson, in any school it is possible to see dolphins rolling up to breathe, leaping out in smooth arcs to re-enter head first, splashing down on their heads and backs, pounding on the water with their chins and flukes, or zigzagging along just beneath the surface. They usually breathe several times each minute, but have been known to dive for as long as five minutes.
“They readily come to bowride, shifting restlessly in the pressure wave to find the best position, often rolling over on their sides to look up at the humans. The speed of the ship seems to present no problems. A group of them were once seen at the bow of a destroyer in the Mediterranean travelling at 64 kph. A school, often with calves travelling in tender, may bowride for twenty minutes or more.”
Scientists have often asked the question as to how the dolphins are able to move so effectively, efficiently and at such speed. Soviet scientists who carried out extensive investigations into this aspect observed that in active swimming, all the dolphin layers of skin interact with the flowing current. They do so in such a way as to result in a reduction of hydrodynamic resistance. This is promoted by highly sensitive receptors that catch the slightest changes of water resistance in any part of the skin surface.
Due to vascular system mobility, the elasticity and other physio-mechanical skin characteristics alter, resulting in turbulence reduction in the onrushing current. The conclusion the scientists have drawn from this observation is that in the dolphins all skin layers interact with each other. The signals about the character of the current trigger the automatic regulation of the mechanical skin properties and as a consequence, the resistance to swimming declines; the higher the speed the lower the resistance becomes.
The practical importance of this study opened up extensive possibilities to work out artificial skins or covers capable of significantly reducing both hydrodynamic resistance and vibrations. These covers may prove useful in the further development of underwater mechanisms for fishermen and seabed explorers with resistance to movement and noise lower than those in the existing models. The world of dolphins has much to offer the humans to study and understand the marine environment better.
In many areas, the Bottlenose Dolphins, known to make much out of bowriding, follow trawlers and shrimp boats feeding on fish stirred up or discarded by the nets. But they can easily hunt on their own. This was well illustrated by an incident observed by Dr Watson in the Black Sea.
A group of Bottlenose Dolphins chased a school of bluefish into a shallow bay and held it there by deploying two of their number to act as sentinels while the rest hung back outside the bay and took turns to feed on them. As a social unit, the Bottlenose Dolphins move around in a group of about twelve to fifteen but there are records of as many as a thousand.
Among the most interesting and clownish of the dolphins, a group of untrained Bottlenose Dolphins in captivity in South Africa were known to regularly mimic fur seals, skate and loggerhead turtles.
In one case, using a seagull feather held in its beak as a scraper, one of the dolphins imitated the actions of a human diver cleaning the side of a glass on underwater portholes, complete with vivid imitation of the sound involved in the cleaning and the breathing of the man through the aqualung, bubbles and all.
“The Bottlenose actually performed this task so effectively that, after just one demonstration, it was never necessary for a diver to do that job again.” Dr Watson has also related another interesting incident, which is perhaps very typical of the dolphins.
In what he calls the “most devastating example of mimicry that has been encountered in any animal,” a young Bottlenose Dolphin seeing a human observer blowing clouds of cigarette smoke in an idle offhand manner outside one of the viewing ports, sought its mother, returned with a mouth full of milk, waited until the smoker was at the window again and then blew the milk out in a cloud against the glass. This action produced precisely the same effect underwater that the smoke had in the air.
There are countless numbers of stories about dolphins safe-navigating sailors through many treacherous waters particularly in and around the regions of Panama: some of them are indeed most touching incredible acts of chivalry.
These examples alone indicate to the humans as to why the world of the dolphins in particular and the cetaceans in general is one that has been around for twenty million years. The human beings have clocked 500,000 years and are already struggling to survive. If the humans will learn from the dolphins they may not only save the cetaceans but in the process ensure their own future too. It is therefore vital that through the thoughtlessness of the humans, the cetaceans should never disappear from the face of the earth.
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