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| 人类对大鲨鱼的肆意捕杀破坏了整个海洋生态的平衡，造成海洋食物链一连串的反应……请尊重我们的自然，请保护地球的有限资源！ Dramatic declines of large North Atlantic sharks due to overfishing have upset the balance of entire marine ecosystems, a new study shows. Now scallops1), clams2) and oysters are paying the price. Smaller sharks, skates3), and rays4) that are normally eaten by the large sharks have become so abundant that they are ravaging5) shellfish stocks, the researchers say. The shark declines, fed by growing worldwide demand for shark-fin soup, are indirectly causing some scallop fisheries to collapse entirely, the scientists add. Wholesale Declines A 2003 study by Julie Baum and fellow Dalhousie biologist Ransom Myers used fisheries?logbooks6)to track severe declines in large sharks since the 1980s. In the new research, Myers, Baum, and three other marine biologists compiled7) additional fisheries?records and independent research surveys going back to the 1970s to reveal that the original study underestimated the declines. “This time we saw some species declining by 99 percent and more,” said co-author Charles Peterson, a biologist at the University of North Carolina. What was most alarming was that all 11 major species of predatory shark — including sandbar, blacktip, tiger, hammerhead, and bull sharks — drastically declined, Peterson said. “As a consequence we can explain why 12 of their 14 prey shark and rays species shot up in abundance in the same time frame,” he added. One species to benefit from the shark declines is the cownose ray, which has increased 20-fold8) in the last 30 years to around 40 million individuals. But the shellfish they feed on have been suffering. “Herds of rays may destroy seagrass beds as they go through looking for smaller buried mollusks9),” Baum, of Dalhousie University, said. “Our concerns are now that the cascade is going to continue one step further and threaten crucial nursery habitats for many marine species.” Worrying New Plans Eager to turn disaster into profit, U.S. entrepreneurs are now moving to establish cownose ray fisheries and promote new markets. That’s exactly the same situation as the early 1980s, when other sharks were regarded as an underutilized10) resource, Baum said. But just two decades later there’s a very real possibility of their extinction in the Northwest Atlantic. Furthermore, the World Conservation Union’s Sarah Fowler added, “recovery in the predatory sharks will not happen if some of their most important prey—the rays — have also been depleted11).” “This study,”Baum noted, “underlines the need to consider ecosystems as a whole.” 一项新的研究表明，由于过度捕捞，北大西洋中的大鲨鱼数量急剧减少，这一情况已经打破了整个海洋生态系统的平衡。现在，扇贝、蛤和牡蛎都在为此付出代价。 研究者们说，小型的鲨鱼、鳐和鱼通常是大鲨鱼口中的食物，如今它们的数量变得十分巨大，正在大肆破坏水生贝类资源。 科学家们补充说，由于世界范围内对鱼翅羹需求的不断增长，使得鲨鱼数量减少，这间接导致一些扇贝渔业全面陷入瘫痪。 数量大规模减少 2003年，朱莉·鲍姆和同事——达尔豪西大学的生物学家兰塞姆·迈尔斯进行了一项研究，利用渔业航海日志来跟踪了解自20世纪80年代以来大鲨鱼数量急剧减少的情况。 在新的研究中，迈尔斯、鲍姆，以及其他三位海洋生物学家把自20世纪70年代以来更多的渔业记录和独立研究调查汇编了进去，结果表明，先前的那项研究低估了大鲨鱼数量的减少。 “这一次我们了解到一些种类的鲨鱼数量减少了99%以上。”论文合著者查尔斯·彼得森说，他是北卡罗来纳州大学的一名生物学家。 彼得森说，最令人震惊的是，所有11种主要的食肉鲨鱼的数量都大幅度减少了，其中包括：阔口真鲨、侧条真鲨、鼬鲨、无沟双髻鲨以及公牛真鲨。 “因此，我们便能解释在作为大型鲨鱼主要捕食对象的14种鲨鱼和鱼中，为什么会有12种在同一时期数量增长极为迅猛。”他补充说。 从(捕食型)鲨鱼的数量减少中获益的一种鱼是大西洋牛鼻鲼，在过去的30年中它们的数量增长了20倍，达到了四千万头左右。但是，被它们当作食物的水生贝壳类动物却遭了殃。 达尔豪西大学的鲍姆说：“成群的鱼四处搜寻隐藏在海底的那些更小的软体动物，这可能会使海草生长的海床遭到破坏。” “我们现在的担心就是：这种一连串的影响会向前更进一步，威胁到对很多海洋物种极其重要的繁殖栖息地。” 令人担忧的新计划 美国的企业家们急于把灾难转化为利润，他们正建立以大西洋牛鼻鲼为捕捞对象的渔业，并努力开发新的市场。 鲍姆说，现在这种情形恰恰就同20世纪80年代早期的情形一样，当时的人认为其他品种的鲨鱼是还未被利用的资源。 但是，仅仅20年后，那些生活在大西洋西北海域的鲨鱼就真有可能消亡了。 此外，世界与自然资源保护联合会的莎拉·福勒说，“如果捕食型鲨鱼最重要的捕食对象——鱼——也被耗竭的话，那么捕食型鲨鱼的数量就不可能恢复。” “这项研究，”鲍姆说，“突显了把生态系统作为一个整体来考虑的必要性。”  |
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