IELTS Academic Reading Practice Test 1: Passage 1

Floating on its back among the waves, cracking open a shellfish on its chest, the sea otter is one of the most familiar animals of the North Pacific coast. Its range once stretched in a long arc from northern Japan, through the Aleutian Islands and Alaska, and down the western coast of North America as far as Mexico. Today the sea otter is also one of the clearest examples of how the fortunes of a single species can shape an entire coastal environment.

Although the sea otter is the heaviest member of the weasel family, it is one of the smallest marine mammals, and this creates a problem. Most animals that live in cold seas, such as seals and whales, are kept warm by blubber, a thick layer of fat beneath the skin. Sea otters have almost none. Instead, they depend on their fur, which is the densest of any animal in the world. Air trapped among the hairs forms an insulating layer that keeps the cold water away from the skin. For this system to work, the fur must be kept perfectly clean, so otters spend a large part of each day grooming, a task that involves rubbing the fur and blowing air into it.

Keeping warm also demands a great deal of energy, and to fuel their bodies, sea otters must eat roughly a quarter of their own body weight every day. They dive to the sea floor to collect sea urchins, crabs, clams, mussels and snails, which they carry back to the surface in loose folds of skin under their front legs. Some individuals use stones as tools, balancing one on their chest and striking shells against it until they break. When resting, otters often gather in groups known as rafts, and they may wrap themselves in strands of kelp, a large brown seaweed, so that they do not drift away while they sleep.

Unfortunately for the sea otter, the fur that protects it from the cold also made it extremely valuable to people. After members of a Russian expedition returned from the North Pacific with otter pelts in the 1740s, a commercial trade developed rapidly. Russian, British and American hunters pursued the animals along the entire coast, and the pelts were sold for high prices, particularly in China. Over the following century and a half, the population collapsed. By the early twentieth century, the species survived only in a handful of small, isolated colonies, and in many places it had disappeared completely.

In 1911, an international treaty finally gave the animals legal protection by banning hunting for commercial purposes. Recovery, however, was slow. Along the coast of California, the sea otter was widely believed to be extinct until 1938, when the existence of a small group off the Big Sur coast was made public. In later decades, wildlife agencies tried to speed up the process by moving otters from Alaska, where numbers had grown, to parts of the coast where they had vanished. Some of these relocations, such as those to British Columbia and Washington, led to growing populations, while others failed.

It was only when otters began to return that scientists came to appreciate their importance. Sea urchins feed on kelp, and when nothing controls their numbers, they can strip the sea floor bare, turning rich underwater forests into what are known as 'urchin barrens'. In the 1970s, researchers working in the Aleutian Islands compared islands where otters had recovered with others where they were still absent. Around the islands with otters, urchins were small and scarce and kelp grew thickly; where otters were missing, urchins were abundant and kelp was rare. The sea otter has since become a textbook example of a 'keystone species', one whose effect on its surroundings is far greater than its numbers alone would suggest.

Healthy kelp forests matter to many other creatures. They provide shelter and food for a wide variety of fish and invertebrates, help to reduce the force of waves reaching the shore, and absorb carbon dioxide as they grow. More recently, research in a Californian estuary has suggested that otters may benefit seagrass meadows too. By eating crabs, otters allow the numbers of certain small animals that feed on the algae growing on seagrass leaves to increase, and with less algae blocking the light, the seagrass is able to thrive.

The return of the sea otter has not been welcomed by everyone. Because the animals eat so much shellfish, people who make a living from harvesting crabs, clams and sea urchins have sometimes seen their catches fall as otters have spread into new areas. Otters also remain vulnerable. Their dependence on fur makes oil especially dangerous to them: once their coats are soaked with oil, they lose their insulation and may quickly die of cold. The 1989 oil spill in Prince William Sound, Alaska, killed large numbers of otters. In parts of south-west Alaska, numbers fell sharply again in the 1990s, for reasons that scientists still debate.