Gentle giants that are vulnerable to human action
I saw it then: a huge, grey-blue mountain in the ocean. I raised my camera and looked through the viewfinder to take a picture. I could not fit the thing into the frame: it was just enormous. Understandably, as this was the largest animal that ever lived: the Great blue whale (Balaenoptera musculus).
A Great blue whale diving, showing its tail fluke, Mirissa. © Niroshan Mirando
Great blue whales are mammals, belonging to the group Cetacea. The root cetus originated from the Greek word ketos meaning ‘sea monster’. Cetaceans are highly specialised for a completely aquatic life, evolving from four-legged land mammals that moved to the sea in search of food some 50-60 million years ago.
Mammals are a group of animals that can regulate their internal body temperature i.e., they are ‘warm-blooded’; they breathe air through their lungs; and female mammals give birth to live young and feed them with milk produced from specialised sweat glands.
Cetaceans have evolved many special adaptations as mammals to live completely in water. These fall into two categories: adaptations to swim efficiently; and adaptations to breathe air in an aquatic environment.
The primary adaptation for life in water is that they are shaped like fish. (A fish-shape is the streamlined ideal for cutting through water with the least resistance.)
Ask a toddler what a whale is, and he or she is most likely to say ‘a fish’. In fact, many adults live under the misapprehension that cetaceans are fish. Cetaceans lack limbs, and instead have flippers — which look like flaps of skin, but which are supported internally by bones. In the front, a pair of flippers helps the animal to steer; there are no hind limbs. There is a dorsal fin that helps to prevent the animal from rolling and a tail fluke to provide the thrust — in an up down movement — to propel it through the water.
This fish-shape of cetaceans has no neck, no chest nor any other divisions of the body seen in many other mammals. Nothing sticks out, to impede movement in water, not even fur.
However, fur is the insulating material that mammals use to regulate their internal body temperature. So how do cetaceans do so without fur? They have a thick layer of fat — called blubber — under the skin. This layer can be about 50 centimetres thick in some species and is an efficient thermal insulator.
To breathe under water, but still breathe air like other mammals, cetaceans have many adaptations. Unlike us, they breathe very efficiently. Their nostrils are on top of their heads and are called a blowhole. They exhale mightily through this, expelling air forcibly out of their lungs so that all the air with carbon dioxide is sent out of the lungs. This is called the ‘blow’.
Cetaceans come to the surface to inhale and then dive. It is when they dive that these adaptations kick in. Cetaceans have more blood than we have: in humans, blood is about 7% of the body weight, whereas in cetaceans it is about 10-15%. Blood vessels are larger, so they serve as a reservoir for oxygenated blood. There are proportionately more red blood cells, which carry oxygen to various parts of the body.
During a dive, the heart rate slows down. Lungs automatically collapse, forcing air out of the lungs. The blood supply to tissues that can tolerate less oxygen (such as the digestive system, muscles and skin) is reduced to 1/10th to 1/20th of the normal amount. Most of the oxygen is shunted to the heart and the brain.
Cetaceans are either filter feeders or feed on fish or large invertebrates. Among the cetaceans there are two groups: baleen and toothed whales. All cetaceans — whales, dolphins and porpoises — are classed within these two groups.
Baleen whales filter the water on the surface of seas and obtain microscopic animals from this process. Baleen is like a large comb that hangs down from the upper jaw of these whales. It feels like a brush and is made out of the same substance as hair and fingernails. These whales lack teeth. Water is drawn in through the mouth and out through the baleen plates, which act like gigantic sieves to filter out microscopic animals. Great blue whales feed on krill, a tiny crustacean. However, in order to provide adequate energy for their enormous bodies, Great blue whales eat four tons of krill per day!
The toothed whales feed on fish and other large invertebrates — such as squid. Sperm whales feed on giant squid and octopuses, diving to great depths to find them. Like the Great blue whale, they need a lot of sustenance: nearly one ton of food per day. Moby Dick was a sperm whale.
Cetaceans are social animals that live in groups — called pods — that include females and their calves. They use complex vocalisations to communicate. Sight and smell are less useful in water than sound. Sound carries well through the dense medium of water, and cetaceans therefore, use hearing extensively. They use high frequency clicks to echolocate — much like bats do on land — to locate prey and find out about their environment. They also whistle to communicate with each other. Certain species of cetaceans — notably the male Humpback whales (Megaptera novaeangliae) — produce complex songs, each 10-20 minutes long, which they repeat for many hours. It is thought that these songs are used to attract females.
Despite these amazing adaptations, cetacean reproduction has left them vulnerable to the impact of human actions. As mammals, cetacean females give birth to live young, feed them with milk produced from their bodies and look after them until they are grown. It can take anything from 2-30 years for cetaceans to mature and females give birth only every 2-3 years. Pregnancy can vary from 8-16 months. A single calf is born and fed on its mother’s milk from 1-3 years, depending on the species. A female cetacean can have only about 11 calves in her lifetime, while a fish can lay a million eggs each year.
Since 3000 BC, whales have been hunted for their meat and blubber — which yielded oil. Industrial whaling — with fleets of ships hunting whales — commenced in the 17th century. The blubber from a single Great blue whale could yield 120 barrels of oil and these cetaceans were killed in the thousands. This killing peaked in 1939 when 29,000 were slaughtered. Demand far exceeded supply, and hunting, by this time, was by no means sustainable. By 1966, the International Whaling Commission set a moratorium and a quota system worldwide for killing whales to allow stocks to recover. Many countries have ratified the convention banning whaling. Notable exceptions are Canada (although hunting is only carried out by the Inuit community), Greenland, Iceland and the Faroe Islands.
But recovery of these decimated populations has been very slow. A multitude of other human actions is now threatening these gentle giants. Noise pollution in the sea — from ships, sonar and other human activities — appears to be disrupting cetacean communication, which relies so heavily on sound. In addition, these animals swim in a polluted — sometimes toxic — soup that we dump into the oceans, and often accumulate these toxins into their bodies.
As the number of ships plying the oceans increase, cetaceans are losing their habitats. There are fatal collisions with ships. The Gangetic River Dolphin (Platanista gangetica gagentica), found in the Ganges and Brahmaputra rivers, is Endangered because of loss of habitat. At least 50 dams have been constructed within the historical range of this animal, drastically reducing available habitat.
Another major threat to cetaceans is accidental entrapment in fishing nets. Unlike fish, these animals cannot breathe dissolved oxygen in water, and slowly and painfully suffocate. It is estimated that some 300,000 marine animals die from entanglement in nets.
What is perhaps the most insidious threat to these gentle giants is climate change. Climate change is altering ocean currents in terms of how heat is distributed, and this will not only affect the food supplies of these species, but also their migratory patterns.
Sri Lanka boasts of 27 species of cetaceans in its seas. But as with other flora and fauna of our island, we are not affording them the protection they need. These specialised mammals are harpooned and netted in by-catches on the coast and their flesh sold inland. We use our oceans as a dumping ground for solid waste, sewage and chemicals. We are opening more and more ports that increase shipping traffic. We ‘watch’ these amazing animals in Mirissa, Trincomalee and Kalpitiya without ensuring that these animals are not harassed in the process of this whale watching.
We need to be more committed to the conservation of cetaceans. As the onetime James Bond, Pierce Brosnan said ‘We owe it to our children to be better stewards of the environment. The alternative? — a world without whales. It’s too terrible to imagine.”