Marine Mammals in the Seas of Sri Lanka
BEAUTY AND VULNERABILITY: There are four groups of marine mammals in the seas around Sri Lanka. They are the Whales, Dolphins, Porpoises and Dugongs. Since the first three groups belong to the scientific order Cetacea, they are referred to as cetaceans.
The word Cetacea is derived from the Greek word Ketos, which means sea monster. Whales, Dolphins and Porpoises have evolved from forebears who were terrestrial many years ago. The Dugong too was terrestrial long years ago.
However it is not a cetacean but belongs to the order Sirenia also includes the Monateees, which are not found in Sri Lanka.
At present there are two sub-orders of Cetaceans, Mysticeti and Odontoceti. Earlier there was another sub-order, Archaeoceti, but the whales in this group became extinct over ten million years ago.
Whales, dolphins, porpoises and dugongs are, unlike fish, warm-blooded mammals, which breathe in air and produce live young. They feed mainly on different types of fish depending on the species and also on zooplankton.
There are 27 species of cetaceans in Sri Lanka, including Six species of large whales.
The whale is called Thalmaha in Sinhala. Whales, belonging to the Mysticeti group, are known as Baleen whales because on the two sides of their upper jaw they have baleen plates, which are like curtains. The baleen plates are the modified teeth of the upper jaw.
The whales consume the food that has been filtered through the baleen plates. Whales, belonging to the sub-order Odontoceti, have teeth with which they catch their food that they hunt and consume.
Another physical difference between these two groups is that the Mysticeti whales have two blowholes at the top of their head whilst those in the other group have only one hole through which they breathe.
The jaws of some dolphins are extended and shaped to enable them to catch fish. Of the 6 species of large whales 5 are baleen whales and the other is a toothed whale.
These marine mammals live in the sea all their lives, and unlike other mammals they do not live on land at all. They have to eat, sleep, travel, reproduce and suckle their young in a marine environment to which they have adequately adapted themselves over time.
This evolution and adaptation has been taking place over the past 50 million years. However, like the majority of other mammals they bear live young, suckle them to give them milk as nourishment and look after their young to adulthood.
All these marine mammals were land mammals many millions of years ago. They, however, took to a life in the sea and evolved into the marine mammals they are now. The whales are the largest mammals ever to have inhabited the earth.
Sri Lanka is very lucky in that within a few hours you can see the largest land mammal, the elephant, at Minneriya National Park or even further east and the largest marine mammal, the whale, in the seas off Trincomalee.
Anouk Ilangakoon, in her book, Whales & Dolphins in Sri Lanka, states, “Their terrestrial origins are betrayed, however, by vestigial bones from the hind legs, which can be seen embedded in the side muscles.
Other mammalian body parts such as the mammary glands and genitals have become internalized and now situated within slits in the body wall. The external ear too has disappeared leaving only a tiny opening, flush with the skin, to reduce drag whilst swimming.
Whales, dolphins and porpoises have also almost completely lost the external hair, which is a normal characteristic of all terrestrial mammals. Occasionally sparse hair can be seen on the snout of young animals but generally the skin is smooth”.
Since they have to breathe in air, they have lungs but their nostrils have, through evolution, moved to the top of their heads to suit their aquatic life. They ‘blow’ the air out through these nostrils. This blowing can be seen easily when watching whales.
The nostrils are now at the top of the head so that the whale, dolphin and porpoise need only to rise to the surface whilst moving forward, blow out, breathe in and dive to a lower depth.
They are, however, able to dive to great depths, sometimes down to the ocean bed, and stay down for long periods when in search of their food. They have adapted physiologically to meet these needs.
The tails of whales, dolphins and porpoises are flattened. This enables them to swim by moving the tails in an up and down motion. This flattened tail is also referred to as a fluke.
All three species have a highly developed sense of hearing. Whales, dolphins and porpoises have a highly developed system of communication, which is operative mostly at a low frequency.
Communication between marine mammals is complex. The ‘language’ in many cetaceans involves elaborate sequences of low-pitched moans or ‘songs’ which can travel considerable distances across oceans.
It may also be used for navigation or high pitched clicks and whistles for short range communication and echo location.
Surface activities may also be associated with communication, including tail-slapping, breaching (leaping clear of the water), ‘spy-hopping (hanging vertically in the water with the head at the surface) and other postures.
Marine mammals give birth to live young, which they feed on milk from the mammary glands. The gestation period of the larger whales can be from 10-16 months but are certainly much shorter than the elephant whose gestation period is 22 months.
Though there is a great diversity of physical forms amongst the whales and dolphins, there are also a number of similarities. Dolphins and porpoises look very much alike.
The whales and porpoises are only found in the sea whereas dolphins are found in many rivers in Asia and in countries like India, Vietnam, Laos etc. Sri Lanka does not have any river dolphins.
Some river dolphins do not come completely out of the water when swimming, as the dolphins that live in the sea do. Some river dolphins, due to the murky water in which they live, are blind since there is no use for their eyes. However, there are other species of river dolphins that have sight.
In baleen whales the females tend to be larger than the males. In some species of toothed whales the males are larger. Some male toothed whales have other distinguishing features such as larger fins (e.g., killer whales) or distinctive teeth (e.g. beaked whales).
A good look at the genital apparatus of a beached specimen will reveal a cetacean’s sex. All sexual organs are internal, the genital slit in males is positioned midway between the navel and the anus, whereas that of the females is much farther back, generally joined to the anal slit, with a smaller mammary slit on either side.
Baleen whales are capable of expanding their pleated throats, allowing them to take enormous gulps of water. Water is filtered through baleen plates, which hang from the top jaw, and the food, which remains, is swept backwards by the large tongue.
Whales are found stranded on our beaches quite often. They are those that have died at sea, due to various reasons, and have been washed ashore.
However, rarely a live whale, or sometimes more than one, is found stranded on the beach. The reason for this is difficult to ascertain but it may be due to the reduction in their buoyancy in shallow waters.
Maybe they are ill, lost their ability to communicate, got disoriented after an accident at sea or some such reason. Such stranded whales should be kept wet by pouring sea water on them regularly. Each specimen that is beached has to be looked at as an individual case and action taken accordingly.
Some may need treatment and recovery maybe possible. some may die eventually and some can be towed out gently when the tide rises, to the deeper parts of the sea.
Even though there is a ban on the hunting of whales, they are still hunted for their meat and oil from blubber, especially by the Japanese. Blubber is a thick layer of fat that whales, being warm-blooded animals, need to regulate their body temperatures when in a cold environment.
Whales live longer and have a low reproductive life cycle in that they take a long period to produce their young. This makes them vulnerable to extinction due to the over exploitation of whales by hunters.
The International Whaling Commission is the only international regulatory body responsible for the management of whales and cetaceans.
The International Whaling Commission has a difficult task to regulate the stocks of the whales, especially those that are close to extinction, because a group of countries are lobbying very strongly for whaling, which they have been doing for a long time, to continue.
Dolphins and Porpoises
Both Dolphins and Porpoises belong to the suborder Odontoceti. Members of this order possess teeth, a single blowhole, and sometimes exhibit sexual dimorphism. Odontocetes also possess bilaterally asymmetrical skulls that often support a well developed bulbous forehead.
Most odontocetes are more social than other groups of cetaceans and use echolocation for navigation. Echolocation is the use of sound waves bounced off on objects. It is also used to locate shoals of fish for food.
These similarities often lead to a misconception about the dolphins and the porpoises. Although the terms ‘dolphin’ and ‘porpoise’ are often used interchangeably, they describe two different groups of cetaceans.
Dolphins belong to the Family Delphinidae, while porpoises belong to the Family Phocoenidae. Many external characteristics that are useful in distinguishing these two families exist. For example, the extended beak present in most dolphins is absent in most porpoises.
All dolphins and porpoises have a melon.
Some members of both families lack dorsal fins altogether. The teeth of dolphins and porpoises are distinct from one another. Dolphins possess homodont conical teeth in their jaws.
Some dolphins have teeth in only one jaw whilst others have teeth in both jaws. Porpoises posses spatulate, or spade-shaped, teeth in both jaws. Homodont is where the species has one type of teeth. Humans have four types of teeth and are hetrodont.
Large schools of finless porpoises have been observed but they are porpoises which are seen in groups of one or two individuals. Dolphins move about in sizeable groups. Dolphins can often be seen performing acrobatics, such as breaching, or leaping out of the water and returning with a splash.
Similarly, many dolphins can be observed bow-riding, riding on the pressure wave of a large ship or whale. Unlike dolphins, porpoises are rarely seen bow-riding.
Dolphins can live to about 40 years. The skin of the dolphins looks smooth but they have tiny ridges to allow the water to flow off and allow them to swim swiftly through the water. They have strong tail muscles that assist in their movements in water. They are graceful social animals.
Many dolphins rely on speed, agility and cooperation within well- organized hunting packs to catch their prey.
Observation of spinner dolphins off Muscat island feeding on tight balls of schooling sardines, showed the dolphins to be swimming through the school in sequential droves of three to four individuals, each seizing a mouthful of fish. Other dolphins circled around, herding the fish together, and awaiting their turn to feed.
Fishermen now, due to an increasing market for their flesh, catch dolphins and porpoises. Anouk Ilangakoon, says “Basically the dolphin harpoon fishery has come about in the last 20 years. With dolphins getting caught in the gillnets, people started consuming dolphins-therefore the market grew”.
Now that there is a market andfishermen in certain areas have resorted to this direct harpooning technique of taking dolphins. It happens only in some areas in the country, mainly on the south coast but has spread to areas on the west coast as well.
However, within the past ten years or so, this practice has spread further. Dolphin flesh is cheaper than the more popular kinds of fish.
It is necessary that an awareness is created amongst the people, especially those consuming their meat, and the threats to their populations highlighted.
This awareness will enable them to have a better understanding of the species. This would create public concern within the country and this concern would go a long way towards the conservation of these marine mammals.
The Dugaong (Dugong dugon) is called Mudu ura and in Tamil Kadal Pandi, both meaning sea pig.
The Dugong, or Sea Cow, as it is also known, is a large herbivorous mammal that lives in the sea entirely. The lip is fleshy and flat like a pad with a few hairs on it. Dugongs breathe from two nostrils at the front of its head. They feed in shallow water on a vegetarian diet consisting mostly of sea grass.
There are only a four species of Sirenians in the world. The dugong is the only Sirenian in the seas around Sri Lanka.
Here, too, they are found only off the North Western coastline from Puttalam to Jaffna and mainly off Mannar. Dugongs live close to the coast and prefer Puttalam to Jaffna coastline habitat since the extensive continental shelf here and the shallow waters provide ideal feeding grounds.
They have well developed mammary glands and have fooled sailors in the past into thinking that they are mermaids. They are sluggish harmless animals.
The dugong has a streamlined body to enable it to swim easily. Its fore-limbs are paddle shaped flippers. The tail fin, like in the Cetacens, is horizontal and flattened. It has a smooth and thick skin. They have small eyes compared to the rest of the body. The ears are two small holes with no covering.
Though dugongs are now extremely rare, they were once plentiful in these habitats, especially during the 19th century and the early part of the past century. Their numbers have greatly reduced due to fishermen catching them.
There is recent evidence that many dugongs were captured annually. Their flesh is in demand and hence their vulnerability. The rate of reproduction of the dugong is low and this contributes to the decline in numbers of this over-exploited mammal.
No real estimates have been made in recent times so that there is no inkling of the population status of the dugongs in their habitat. There is a great danger of the dugong quietly slipping to extinction due to the fact that it is rarely seen and that too by very few.
All cetaceans found in Sri Lankan waters and the dugong are protected by two ordinances, the Flora and Fauna Protection Ordinance and the Fisheries Act.
However, the law is rarely enforced and is in effect useless in terms of conserving these species. If there is to be a positive effect in the attempt to conserve these species, there must be an active campaign by the knowledgeable public and the law, as it stands, implemented.
If the law is found to be inadequate, to deal with the situation under present circumstances, the necessary amendments to the laws should be brought in.
(Since I am not fully versed with marine mammals, I have sought the assistance of Ms Anouk Ilangakoon, a longtime researcher of marine mammals, to look at this article)