2021年7月1日雅思考试机经回忆完整版(4)

2023-06-08 15:58:22 来源：中国教育在线

2021年7月1日雅思考试机经回忆完整版(4) 关于这个问题下面小编就来为各个考生解答下。

2021年7月1日雅思考试机经回忆完整版(4)

2021.07.01

READING

Passage 3

Topic

Killer whale

Issues Affecting the Southern Resident Orcas

Orcas, also known as killer whales, are opportunistic feeders, which means they will take a variety of dfferent prey species. J, K and L pods (specilfie groups of orcas found in the

region) are almost exclusively fish eaters. Some studies show that up to 90% of thelr diet is salmon, with Chinook salmon being far and away their favorite. During the last 50 years,

hundreds of wild runs of salmon have become extinct due to habitat loss and overfishing of wild stocks. Many of the extinct salmon stocks are the winter runs of chinook and coho,

Although the surviving stocks have probably been suficient to sustain the resident pods, many of the runs that have been lost were undoubtedly traditional resources favored by the

resident orcas. This may be affecting the whale's nutrition in the winter and many require them to change their patterns of movement in order to search for food.

Toxic substances accumulate in higher concentrations as they move up the food chain, Because orcas are the top predator in the ocean and are at the top of several different food

chains in the environment, they tend to be more affected by pollutants than other sea creatures. Examinations of stranded kller whales have shown some extremely high levels|

of lead, mercury and polychlorianted hydrocarbans. Abondoned marine toxic waste dumps and present levels of industrial and human reluse pollution of the inland waters probably

presents the most serious threat to the continued existence of this orca population. Unfortunately, the total remedy to this huge problem would be broad societal changes on

many fronts. But because of the fact that orcas are so popular, they may be the best species to use as a focal point in bringing about the many changes that need to be made in

order to protect the marine environment as a whole from further toxic poisoning.

The waters around the San Juan islands are extremely busy due to intermational commercial shipping, fishing, whale watching, and pleasure boating. On a busy weekend day in the summer, it is not uncommon to see numerous boats in the vicinity of the whales as they travel through the area. The potential impacts from all this vessel trfflc with regard to the whales and other marine animals in the area could be tremendous. The surfacing and breathing space of marine birds and mammals is a critical aspect of their habitat, which the animals must consciously deal with on a moment-to-moment basis throughout their lifetimes. With all the boating activity in the vicinity, there are three ways in which surface impacts are most likely to affect marine animals: (a) collision (b) collision avoldance, and (C) exhaust emissions in breathing pockets. The first two impacts are very obvious and don't just apply to vessels with motors. Kayakers even present a problem here because they're so quiet. Marine animals busy hunting and feeding under the surface of the water, may not be aware that there is a kayak above them and actually hit the bottom of it as they surface to breathe. The third impact is one most people don't even think of, When there are numerous boats in the area, especially idling boats, there are a lot of exhaust fumes being spewed out on the surface of the water. When the whale comes up to take a nice big breath of "fresh" air, it instead gets a nice big breath of exhaust fumes. It's hard to say how greatly this affects the animals, but think how breathing polluted air affects us (i.e. smog in large cities like Los Angeles, breathing the foul air while stting in taffie jams, etc.).

D，

Similar to surface impacts, a primary source of acoustic pollution for this population of orcas would also be derived from the cumulative underwater noise of vessel taffc. For

cetaceans, the underwater sound environment is perhaps the most critical component of their sensory and behavioral lvs, Orcas communicate with each other over short and long distances with a variely of clicks， chirps, squeaks, and whisles, along with using echolocation to locate prey and to navigate. They may also rely on passive listening as a primary sensory source. The long-tem impact from noise pollution would not likely show up as noticeable behavioral changes in habitat use, but rather as sensory damage or gradual reduction in population health. A new study at the Whale Museum called the SeaSound Remote Sensing Network has begun studying undenwater acoustics and its relationship to orca communication.

27-30 LOH题

List of headings

i Top Ocean Predators

i Toxic Exposure

li Declining Fish Population

iv Pleasure Boating in the San Juan Islands

v Underwater noise

Vi Smog in Large Cities

Vii Impact of Boat Traffic

27 SectionA ii

28 Secion B ii

29 SectinC vii