2014年5月雅思考试模拟试题及答案(第六套)_第8页

　　SECTION 4

　　You’ll hear a talk about an animal called a dugong.

　　First, you have some time to look at questions 31 to 40.

　　[20 seconds]

　　Now listen carefully and answer questions 31 to 40.

　　Today you’re going to hear about one of my favourite animals – the dugong. I’m sure you’ve all seen photographs of, or maybe even documentaries about, this enormous but gentle marine mammal.

　　Now, firstly, a few vital statistics: The dugong can grow up to three metres long and they’re very heavy creatures, weighing in at over 400 kilograms. If they survive without interference or accident, they can reach an age of 70 years or more. You may have heard the dugong called something more familiar – it is often referred to as a sea cow – this is because it is unique among marine mammals in that it is entirely herbivorous. It grazes exclusively on plants and, for this reason, is probably more closely related to the elephant than to other marine mammals such as dolphins or whales.

　　You’ll see, in this first slide [click], that Dugongs are quite rotund and, like the

　　dolphin, they have a flattened fluked tail but, unlike dolphins, they don’t have a dorsal fin on their upper back. They have paddle-shaped flippers (I’ll tell you more about these later) and a quite distinctive head contour. They have very large mouths with an upper lip that is covered in bristles, like whiskers, I suppose. Can you see them? Ah, here, in this slide [click] there is a close-up view of the head and mouth. These

　　bristles play an essential role in their feeding routine – without them they wouldn’t be able to find and nibble on the sea grass which is the mainstay of their diet. They have two nostrils near the front of the head so they can breathe air above the surface of the water whilst their body, or most of it anyway, remains submerged.

　　I’d like to talk a little about their habitat and behaviour, now. Although dugongs can be found in the waters of up to 40 Indo-Pacific countries, it is the Australian

　　population that we will focus on in this talk. They inhabit shallow, warm water off Queensland going all around the northern coast of the continent to WA. There are probably about 80,000 dugongs in these waters. As I said before, they consume aquatic grass – around 50 kilograms a day. You’ll see in this slide [click] how they

　　use their flippers - it looks as though the dugong is actually ‘walking’ on the seabed. Their average swimming speed has been calculated to be around 10 kilometres an hour. Some marine mammals can stay submerged for long periods of time but not so the dugong. Typically, the dugong holds its breath for between one and three maybe, a maximum of, six minutes, depending on the level of its activity.

　　I’m going to move on to talk about the conservation status of the dugong. Dugongs are very slow to mature – and the female only has a calf about once every 5 years. The calf stays with the mother for up to 2 years. There are several natural predators, mostly sharks, which account for most of the juvenile fatalities, but crocodiles and killer whales also kill dugongs. However, as is the case with so many endangered species, it’s us, humans, who are the main threat to their survival. Of course, they have traditionally been hunted for food, but boat propellers, set nets and habitat destruction are all having serious effects on their numbers. Dugongs are particularly vulnerable because they live in shallow water where they are more likely to get caught in nets; not just fishing nets but, here in Australia, the shark nets. These anti-shark measures have become popular at swimming beaches since the 1960s. Unfortunately, once a dugong becomes entangled in a net, it can’t surface to breathe and drowns. Proponents of the shark nets argue that the number of dugongs being caught in nets is dwindling; however, this is seen by dugong researchers as just another indication of argument for the elimination of shark nets is stronger than ever.

　　NARRATOR: That is the end of section 4. You now have half a minute to check your answers.