Spinner dolphins

Spinner dolphins

Marine Mammals: Whales, Dolphins, Porpoises & Dugongs

Marine mammals in the northern Indian Ocean belong to two distinct groups: cetaceans and sirenians. The former include whales, dolphins and porpoises, while the latter comprises the dugongs. 


Cetacean (pronounced ‘see-tay-shun’) comes from the Greek word ketos, meaning sea monster. A Latinisation of this word, cetus, is used in scientific terminology to mean ‘whale’. Cetacea is the name formally given to the order of placental mammals having a blowhole for breathing and no hind limbs.

Observing marine mammals at close range, we are typically enchanted or awed by what we see. We bond with these wondrous creatures emotionally and aesthetically even as we gain first-hand knowledge about their lives and deeper understanding of the dangers facing them. Increased interest in and sympathy toward marine mammals tends to generate more support for conservation, helping preserve Earth’s marine mammal biodiversity for generations to come.


– Howard Martenstyn

Author 'Out of the Blue'

November 2013

Cetology is the branch of marine science associated with the study of whales, dolphins and porpoises. The name sirenia is derived from the Greek legend of the Sirens.


All cetaceans are divided into two scientific groups, baleen whales and toothed whales, depending on their oral anatomy and manner of feeding. Baleen whales, known to zoologists as belonging to the sub-order Mysticetes, comprise of whales which have ‘plates’ made of a keratinous substance called baleen that hang down from their upper jaws. They also lack teeth. Mysticetes are filter feeders, living on organisms such as plankton, krill and small fish, which they strain out of the water using their baleen plates.


Toothed whales or Odontocetes belonging to the suborder comprise the remaining species of whales, dolphins and porpoises. They are predatory in their feeding habits.



  • Approaching marine mammals too closely disrupting their natural behaviour, including feeding patterns and surfacing time.

  • Entanglement in fishing gear (by-catch) including "ghost" nets

  • Illegal fishing practices (eg. dynamiting, "Leila" nets)

  • Poaching of small animals

  • Ship and other vessel strikes

  • Marine pollution (toxic contamination and stomach disease caused by ingestion of foreign matter such as plastic) 

  • Noise pollution

  • Climate change

  • Electromagnetic radiation and geomagnetic storms

  • Oil and gas development including seismic activity

  • Habitat degradation.

Discovering Marine Mammals


The evolution of cetaceans goes back some 50 million years to the early Eocene period. This order of mammals was originally land-dwelling, with well-developed legs that were slowly lost as the ancestral whales-to-be returned to the sea from which they, like all land animals, originally emerged.

Modern cetaceans and sirenians are all fully aquatic. Their bodies are generally streamlined and fusiform (spindle-shaped) and come in a variety of shapes and sizes. Some are long and slender; others short and stocky. Some have large dorsal fins; others have small or no fins at all. And while a few, like orcas, are brightly and conspicuously marked, others are drab and hard to identify.

Why Protect Whales and Dolphins​

They play an important role in stabilizing the aquatic food chain and reproduction of other species through a benign form of geo engineering. Although they eat tiny fish and animal matter they also keep them alive by feeding at depths and releasing fecal plumes rich in iron and nitrogen at or near the surface. These plumes fertilize plant plankton that live in the sunlit layer.


By plunging up and down through the water column of the ocean, whales and dolphins keep kicking plant matter back up and further into the sunlit layer giving it more time for photosynthesis to occur and reproduce before it sinks again. More plant plankton means more animal plankton and so on through the food chain. In other words more whales and dolphins means more fish and krill.


They can help undo some of the damage we have done to the living system of the sea and to the atmosphere. Plant plankton absorbs Carbon dioxide from the atmosphere and eventually forms massive carbon sinks on the ocean floor (slowing global climate change). A dead whale carcass that sinks to the ocean depths is also important in carbon cycling. The whale fall takes carbon acquired at the surface (usually in the form of plankton) to the ocean depths. The larger the animal, the more carbon-filled tissues it has, meaning that larger whales contain larger carbon reservoirs. Estimates as much as 400,000 tonnes of carbon are extracted from the air due to sperm

whales each year! A whale carcass also provides food for hundreds of organisms usually devoid of such bountiful food resources. 


Whales and dolphins help regulate the flow of food by helping to maintain a stable food chain and ensuring that certain animal species do not overpopulate the ocean and possibly destroy the population of other species that it feeds on.


We learn a lot from cetaceans well known for their high level of intelligence, behaviour, echolocation, communication and environmental impact. This has led to a lot of discoveries and advancements regarding sonar, aquatic environments, marine life/biology and animal intelligence/behaviour and other important oceanic topics. Our growing understanding of them is important for improving conservation measures of all marine mammals as well as improving the oceans ecosystem.


They play an important role in helping growing economies that can depend on whale watching and other marine spectator activities bring in capital and increase profitability through tourism. While whale watching is not a perfect alternative, it is significantly less harmful than unmanaged commercial fishing and provides a much greater economic benefit and alternative. Mirissa is modeled around this concept and has thrived economically as a result.

Marine Mammal Status


Based on current understanding 28 species of marine mammals (11 whales, 15 dolphins, 1 porpoise and the dugong) are known to be found in Sri Lankan waters. In addition, sightings of fin whales, sei whales and minke whales have also been recorded but may have been cases of mistaken identity.


Further scientific research, combined with sightings from whale-and dolphin-watching expedition logs, is likely to reveal or confirm species and/or subspecies. Also, future research may show that a confirmed species may not to be present. Research is also needed to improve the data on population sizes and the distribution of existing species.


Every species belongs to a family grouping. A list of common family names with the number of associated species found in Sri Lankan and adjacent waters is shown in the accompanying tables. The lists of whales, dolphins, porposie and dugong species found in Sri Lankan and adjacent waters are tabulated on this page.


All marine mammals are protected under the Fauna and Flora Protection (Amendment) Act, No. 22 of 2009.

Status of Marine Mammal Species in Sri Lankan & Adjacent Waters

Further reading:

Read more about whale and dolphin watching around Sri Lanka and plan your next trip at the Whale and Dolphin Watching Centre.

Blue whale geographical and depth distribution
Blue whale
Dugong geographical and depth distribution
Omura's whale
Whale Species
Dolphin Species
Porpoise Species
Sirenians - Manatees & Dugongs
Dugong Species

Although IUCN lists the dugong as 'vulnerable', studies indicate that the species is now critically endangered in Sri Lanka.

Marine Mammal Stranding


Every year several marine mammals, alone or in groups, are found stranded alive or dead on Sri Lankan beaches or at sea. Strandings are a natural phenomenon, occurring around the world and recorded through history. Some, nevertheless, are the result of human activity impacting upon the lives of mammals in unfortunate ways, such as fish dynamiting, fisheries by-catch (net entanglement), vessel collisions, acoustic disorientation from shipping and other man made sounds.


A number of natural causes are also known or thought to cause strandings. Among these are:

  • Death from sickness or simply old age, followed by the body simply being washed ashore.

  • Entrapment in shallow water, when the animal is unable to find its way back to the ocean; this sometimes happens after a cow enters shallow water to give birth.

  • An echolocation failure of some kind.

  • Panic and loss of bearings after a storm or seismic event.

  • Disorientation due to physiological causes, such as an infection, external trauma, or the need to rest due to illness.

  • Terrestrial magnetic anomalies, such as those caused by heavy local deposits of iron, interfering with the magnetoceptic navigational sense cetaceans are thought to possess.


Most difficult to explain are mass strandings. It is unknown whether all the stranded individuals are similarly afflicted or disoriented, or whether the whole group follows a single animal that is disoriented, sick or responding to some reproductive imperative such as the need to give birth.

Strandings provide an opportunity to collect marine mammal data that cannot be obtained at sea. For example, the lengths of various parts of the carcass can be measured and the teeth examined. The number, size, shape and location of cetacean teeth can be very distinctive, helping to identify the species of the carcass.


Many marine mammals change colour after death, sometimes within a few hours, giving observers a false impression of their true colouration while alive. Normally, the change involves substantial darkening.

How to Deal with Live Strandings


First, establish that the animal is still alive by listening for its breath (in some species there may be a gap of as much as 15 minutes between breaths) and looking for eye movement. Stranded false killer whales have been measured breathing at 10-42 sec intervals.



  • Get expert help (call the local police) as quickly as possible.

  • Keep the mammal’s skin moist.

  • If possible erect a shelter to provide shade.

  • Keep the flippers and flukes cool.

  • Keep onlookers at a distance.

  • Make as little noise as possible.

  • Try to keep the mammal oriented correctly (back uppermost and its blowhole out of the water).

The main cause of death in live strandings is overheating. In the case of mass strandings, try to return as many cetaceans as possible to the water simultaneously; if not, the animals will beach themselves again in an attempt to rejoin their companions.

Do Not


  • Stand very close to the tail or head.

  • Push or pull on the flippers, flukes or head.

  • Cover the blowhole.

  • Let either water or sand enter the blowhole.

  • Apply lotion to the mammal’s skin.

  • Touch the mammal more than necessary.

Indian Ocean bottlenose dolphin distribution © Howard Martenstyn Out of the Blue