This order of marine creatures is known as cetacea and includes 76 species of whale, dolphin and porpoise. All are highly specialised mammals, living entirely in water, and yet breathing air. They are warm blooded (they control their own body temperatures), and give birth to live young, which the mother suckles on milk secreted by mammary glands. Cetaceans are social animals, and dolphins in particular have a reputation not only for their sociability with each other, but also with humans. Living in groups is thought to be the most efficient way of finding their food - small fish and squid.
Cetaceans are divided into two groups. One of these groups - the toothed whales - includes small whales, dolphins and porpoises, all of which prey on fish and squid. The other group comprises the largest whales, known as baleen whales. Members of this group feed on microscopic sea life called plankton. They extract plankton from the sea by filtering water through 'baleen plates' a special upper jaw adaptation.
Specially adapted to marine life
The shape of cetaceans is ideally suited for moving through water, as their bodies are smooth and streamlined. The front limbs are modified into flippers, there are no visible hind limbs, and the tail is strong, with horizontally set flukes. To help them maintain a stable body temperature in low water temperatures, they have an insulating layer of fat called blubber.
In cetaceans the lungs compress air, driving it into the windpipe and nasal passages. These passages have thick linings preventing nitrogen passing into the tissues which could cause a dangerous condition known as 'the bends'. This condition sometimes affects humans who dive. When the cetacean returns to the surface, its lungs gradually expand and air and waste gases are expelled through an opening on the upper surface of the body known as a blowhole.
The senses
Sound travels more effectively through water than through air and cetaceans rely more upon sound than vision. Their senses of smell and taste are not very well developed. They produce a wide variety of sounds, and use sound both to communicate and to form a 'picture' of their surroundings through 'echolocation' reflecting soundwaves or ultrasonic signals from objects around them. The sounds they emit range from squeaks and clicks to whistles and moans.
The limbs are used primarily for moving through water, but they are also important for touch, and dolphins in particular use their whole bodies for touch sensations.
Cetaceans around Britain Whales were once common around our shores, and commercial whaling used to be an important industry. Minke, fin and sperm whales are still seen occasionally on western coasts, while the smaller toothed whales, dolphins, porpoises and pilot whales are more numerous. Bottlenose dolphins and harbour porpoises are the cetaceans most likely to be seen close to shore, with regular sightings of bottlenose dolphins in the Moray Firth and Cardigan Bay. It is estimated there are about 75,000 common dolphins in the Celtic Sea, but apart from the winter months, they rarely come close enough inshore to be seen from the coast.
A massive decline in overall numbers means the English Channel and southern North Sea are hardly ever visited by cetaceans, which now favour Atlantic coasts and islands. This was not always so, and in fact at one time there were porpoise 'fisheries' on the lower Thames, where porpoises were hunted using harpoons.
Your local wildlife trust will be able to advise you on the nearest places to see cetaceans.
Threats to cetaceans
Pollutants in the seas have affected all marine life and certain toxic pollutants can accumulate in the bodies of marine creatures. Research shows that the most common contaminants found in cetaceans are the insecticide DDT; PCBs which are used in the plastics industry; and the heavy metal mercury which can enter the seas via polluted air, or by direct discharge of polluted water into rivers and the sea. These three toxic contaminants are found particularly in cetaceans which feed primarily on fish or squid, and which live in coastal habitats for most or all of the year.
Fishing can also be a threat. Gill nets do not discriminate between species and this can mean that dolphins and porpoises are caught and die needlessly. Cornwall Trust found that harbour porpoises particularly are suffering in this way, and they are working with the fishing industry to find more selective ways to fish.
Cornwall Wildlife Trust has undertaken a special study of dolphins and porpoises. Local fishermen cooperated with the trust in their research and trust observers on the fishing boats took details of cetacean catches in gill nets. The Wildlife Trusts are continuing to research catches of cetaceans by UK fisheries and are investigating means of reducing cetacean deaths caused as a by-product of fishing for edible catches.
Sometimes cetaceans become stranded in shallow water or on beaches. We do not fully understand why this happens, but it has been established that individuals which become stranded are often sick. Group strandings can happen when several members of a group follow a sick individual member ashore. If you spot a stranded cetacean, contact your local wildlife trust. Sometimes groups can be helped back out to sea .
Further contacts and reading
Mammal Society Cetacean Group,
Edward
Grey Institute,
Zoology Department,
Oxford University, South
Parks Road,
Oxford OXl 3PS.
The Seawatch Foundation collects reports from all around the
UK and operates a scheme of regular observers.
The Seawatch Foundation,
7 St. Andrews Lane,
Southwater,
West Sussex RH13 7DY.
Cornwall Wildlife Trust have a free dolphin identification guide.
Send SAE to:
Cornwall Wildlife Trust,
Five Acres,
Allet,
Truro TR4 9DJ.
Further reading:
Eyewitness Guides - Whale. Vassili Papastavrou, published by Dorling Kindersley. £8.99
Whales and Dolphins. Anthony R. Martin and others published by BCA.
If you don't know where to contact your local wildlife trust, then ask The Wildlife Trusts, The Green, Witham Park, Waterside South, Lincoln LN5 7JR Tel: 01522 544400
Did you know...
No two dolphin dorsal fins are the same - so photographs showing this fin on the dolphin's back t are very important in identifying individual dolphins and studying their movements.