Overfishing of one of the ocean’ s top predators has triggered a lethal chain reaction that threatens to decimate populations of bay scallops, oysters, and clams, warns a new study, e Plunging populations of11 large shark species have caused a spike in the numbers of their prey, including smaller sharks, rays and skates．These creatures in turn are wiping out other marine organisms and may be destroying sea grass habitat, which serves as a nursery for many species．
　　 Sharks have had a rough few decades．Demand for their fins and meat has resulted in increasin exploitation, and the creatures are often accidentally captured by swordfish and tuna fishers, As man as 73 million sharks are killed annually, and past studies have indicated many populations have been ct by half．Nonetheless, scientists have had difficulty gauging the decline in several shark species over the years because of a lack of data．The effect of this decline on ocean ecosystems has also proven hard t measure．
　　 To get a better grip on the problem’, marine biologist Julia Baum of Dalhousie University in Halifax Canada, and colleagues trawled 35 years of marine surveys and fisheries data to document declines i large sharks off the eastern seaboard of the U．S．The numbers, reported today in Science, are stark The blacktip shark population has plummeted 93% since 1972, with similar declines for tiger, bull, an smooth hammerhead sharks．
　　 Simultaneously, the abundance of 12 of the 14 species that these sharks prey on--including the litt] skate, the chain catshark, and the cownose ray--increased dramatically．The latter has seen its numbers swell ten-fold．The jump in ray numbers is especially troubling, notes co-author and marine biologist Charles Peterson of the University of North Carolina at Chapel Hill, because the fish shred the sea grass that houses crabs and clams．In fact, he notes, by 2004 ray predation had shut down Nort Carolina’s century-old bay scallop fishery．
　　 The 11 other shark prey species whose populations rose over the 35-year period could be havin similar impacts to that of the cownose ray, says Baum．
　　 The result is profound because the high diversity of fishes in the northwest Atlantic has bee thought to minimize catastrophic changes in the food web, says marine scientist Kenneth Frank of the Bedford Institute of Oceanography in Dartmouth, Canada．Sharks are only part of the puzzle, however Frank warns．People’s appetites for oysters, clams, and scallops are likely having a more direct impact on these populations, he says．[414 words]
　　 1．The overfishing of sharks may result in______
　　 A．the abundance of sea grass habitat
　　 B．the ruin of nursery for many marine species
　　 C．the obvious increase of most marine species
　　 D．the huge decline of the populations of their prey
　　 2．What contributes most to the overfishing of sharks is______
　　 A．the sharks accidentally captured by tuna fishers
　　 B．the rough few decades that sharks have suffered
　　 C．the ever-increasing demand for their fins and meat
　　 D．the millions of sharks killed deliberately each year
　　 3．Julia Baum studied marine surveys and fisheries data in order to______
　　 A．prove the fact that shark populations have fallen sharply
　　 B．cast light on the effect of shark decline on ocean ecosystrems
　　 C．document the shark species which have declined most rapidly
　　 D．understand the subtle relationship between predators and prey
　　 4．The rapid increase of the cownose ray results from______
　　 A．the ten-fold increase of its numbers in a short time
　　 B．the abundance of the 12 species that sharks prey on
　　 C．the tremendous decline of the number of its predators
　　 D．the decline of sharks off the eastern seaboard of America
　　 5．The populations of bay scallops, oysters, and clams are threatened directly by______.examda.
　　 A．the high diversity of fishes in the northwest Atlantic
　　 B．the catastrophic changes in the food web in the Atlantic
　　 C．the lethal reaction triggered by the overfishing of sharks
　　 D．the strong desire of many people for them as their delicious food

　难句透析
　　①Overfishing of one of the ocean’S top predators has triggered a lethal chain reaction Ethat threatens to decimate populations of bay scallops，oysters，and clams]，warns a new study．
　　【结构】“warns a new study”是本句的主句。“Oveffishing of…clams”是“warns”的宾语从句；其中的主语是“0ver fishin9”，谓语动词是“has triggered”。方括号所标示的“that threatens…clams”是“reaction”的后置定语从句。
　　【释义】一项新的研究成果警告说，对于一种海洋顶级食肉动物的过量捕捞已经引起了一串致命的连锁反应，可能将把绝大部分海湾扇贝、牡蛎、蛤蜊灭掉。
　　 ②”Demand for their fins and meat has resulted in increasing exploitation，and”the creatures are often accidentally captured by swordfish and tuna fishers．
　　【结构】本句是由逗号和“and”连接的两个分句组成的并列句。
　　【释义】对鲨鱼鳍和鲨鱼肉的需求导致对鲨鱼的捕捞日益增多；捕捞剑鱼和金枪鱼的渔民也常常偶然捕获鲨鱼。
　　 ③[To get a better grip on the problem]，marine biologist Julia Baum of Dalhousie University in Halifax，Canada， and colleagues trawled 35 years of marine surveys and fisheries data[to document declines in large sharks off the eastern seaboard of the U．S．]．
　　【结构】本句的主语是“marine biologist”，谓语动词是“trawled”。方括号所标示的两个动词不定式短语“To get…problem”和“to document…the U．S．”都是目的状语。
　　【释义】朱莉·鲍姆是位于加拿大哈利法克斯的达尔豪西大学的海洋生物学家。为了更透彻地了解此问题，朱莉·鲍姆和同事们研究了35年的海洋普查资料和渔业资料，以证明美国东海岸外海区的大型鲨鱼数量的减少。
　　 ④Simultaneously，the abundance of l2 0f the l4 species[that these sharks prey on]--including the little skate，the chain catshark，and the cownose ray increased dramatically．
　　【结构】本句的主语是“the abundance”，谓语动词是“increased”。方括号所标示的“that these sharks prey on”是“species”的后置定语从句。破折号之间的部分是对“species”的补充说明。
　　【释义】与此同时，这些鲨鱼捕食的14种海洋生物中，有12种数量急剧增长。其中包括小鳐鱼、网纹猫鲨和牛鼻鲅鱼等。
　　 ⑤“The result is profound”because the hiigh diversity of fishes in the northwest Atlantic has been thought to mini— mize catastrophic changes in the food web3，says marine scientist Kenneth Frank of the Bedford Institute of Ocea nography in Dartmouth，Canada．
　　【结构】方括号所标示的“because the high diversity…has been thought tO minimize…web”是原因状语从句；其中的主语是“the high diversity”，谓语动词是“has been thought”。
　　【释义】肯尼斯·弗兰克是加拿大达特茅斯的贝德福德海洋学研究所的海洋科学家。他说，“其结果影响深远”，因为人们一直认为西北大西洋鱼类品种的高度多样化能最大限度地降低食物网的灾难性变化。
　　 答案注释
　　 1．根据第一段最后一句中的“These creatures…may be destroying sea grass habitat，which serves as a nursery for many species”可知，选项B应为答案。
　　 2．根据第二段第二句“Demand for their fins and meat has resulted in increasing exploitation，…”可知，选项C应为 答案。
　　 3．根据第二段最后一句“The effect of this decline on ocean ecosystems has also proven hard tO measure”，以及第三段第一句“To get a better grip on the problem，marine biologist Julia Baum…trawled 35 years of marine sur— veys and fisheries data…”可知，选项B应为答案。
　　 4．根据第一段第二句“Plunging populations of ll large shark species have caused a spike in the numbers of their prey，includin9…rays…”，以及第四段第一句“…the abundance of…species that these sharks prey on— includin9…the cownose ray--increased dramatically”可知，选项C应为答案。
　　 5．根据本文最后一句“People’S appetites for oysters，clams，and scallops are likely having a more direct impact on these populations，he says”可知，选项D应为答案。

　 全文翻译 　
　　 一项新的研究成果警告说，对于一种海洋顶级食肉动物的过量捕捞已经引起了一串致命的连锁反应，可能将把绝大部分海湾扇贝、牡蛎、蛤蜊灭掉。11种大型鲨鱼物种数量的减少会导致其食物，比如体积较小的鲨鱼、缸和鳐数量急速增加。而这些生物又可能会导致其他海洋生物灭绝，破坏海草生长环境，海草历来是众多海洋物种的滋生地。
　　 过去的几十年是鲨鱼生存的艰难时期。对鲨鱼鳍和鲨鱼肉的需求导致对鲨鱼的捕捞日益增多；捕捞剑鱼和金枪鱼的渔民也常常偶然捕获鲨鱼。每年多达7300万头鲨鱼被捕杀，过去的研究表明许多鲨鱼数量减半。尽管如此，由于数据缺乏，过去多年科学家无法对几种鲨鱼的减少作出准确测算。鲨鱼种类减少对海洋生态系统的影响也很难估量。
　　 朱莉。鲍姆是位于加拿大哈利法克斯的达尔豪西大学的海洋生物学家。为了更透彻地了解此问题，朱莉。鲍姆和同事们研究了35年的海洋普查资料和渔业资料，以证明美国东海岸外海区的大型鲨鱼数量的减少。科学杂志今日报道中的数据显示：黑鳍鲨、老虎、公牛和锤头鲨自1972年后数量骤减93％。
　　 与此同时，这些鲨鱼捕食的14种海洋生物中，有12种数量急剧增长。其中包括小鳐鱼、网纹猫鲨和牛鼻鲅鱼等……增长数量急剧膨胀10倍之多。合著者——北卡罗来纳大学教堂山分校海洋生物学家查里。彼特森指出，觚数量的急速增长十分棘手，因为它们会把螃蟹和蛤栖身的海菜撕碎。他还指出，事实上，2004年以来舡的大量捕食已经导致北加利福尼亚长达百年的海湾扇贝产业倒闭。
　　 鲍姆表示，其他11种鲨鱼食物物种在过去的35年间的大量增长，会产生与东部鲽鲛舡相似的影响。
　　 肯尼斯。弗兰克是加拿大达特茅斯的贝德福德海洋学研究所的海洋科学家。他说，“其结果影响深远”，因为人们一直认为西北大西洋鱼类品种的高度多样化能最大限度地降低食物网的灾难性变化。然而，弗兰克警告说，鲨鱼只是难题的一部分。人们对牡蛎、蛤和扇贝的需求将会对其数量产生更加直接的影响。
　　 超纲词汇
　　 Predator n．捕食者，食肉动物
　　 Decimate vt．每十人杀一人，大批杀害
　　 scallop n．扇贝，干贝
　　 Oyster n．[动]牡蛎，蚝
　　 clam n．蛤
　　 Plunge vt．使投入，使插入，使陷入
　　 shark n．鲨鱼
　　 Spike n．峰值
　　 Ray n．鲅鱼，鳐鱼
　　 Skate n．[动]鳐
　　 Marine adj．海的，海产的
　　 fin n．鳍
　　 Exploitation n．开采，开发
　　 swordfish n．旗鱼，剑鱼
　　 Tuna n．金枪鱼
　　 Gauge vt．估量，评价，判断
　　 trawl vt．水下观测
　　 Stark adj．硬的，完全的，十分明显的
　　 plummet vi．骤然跌落，垂直落下
　　 bull n．公牛，公象，公鲸等
　　 Hammerhead adj．锤头状的
　　 shred v．撕碎，切碎
　　 Crab n．螃蟹
　　 Predation n．捕食作用
　　 Catastrophic adj．悲惨的，灾难的
　　 参考答案：1．B 2．C 3．B 4．C 5．D