首页
登录
职称英语
When prehistoric man arrived in new parts of the world, something strange hap
When prehistoric man arrived in new parts of the world, something strange hap
游客
2023-12-24
33
管理
问题
When prehistoric man arrived in new parts of the world, something strange happened to the large animals: they suddenly became extinct. Smaller species survived. The large, slow-growing animals were easy game, and were quickly hunted to extinction. Now something similar could be happening in the oceans.
That the seas are being overfished has been known for years. What researchers such as Ransom Myers and Boris Worm have shown is just how fast things are changing. They have looked at half a century of data from fisheries around the world. Their methods do not attempt to estimate the actual biomass (the amount of living biological matter) of fish species in particular parts of the ocean, but rather changes in that biomass over time. According to their latest paper published in Nature, the biomass of large predators (animals that kill and eat other animals) in a new fishery is reduced on average by 80% within 15 years of the start of exploitation. In some long-fished areas, it has halved again since then.
Dr. Worm acknowledges that these figures are conservative. One mason for this is that fishing technology has improved. Today’s vessels can find their prey using satellites and sonar, which were not available 50 years ago. That means a higher proportion of what is in the sea is being caught, so the real difference between present and past is likely to be worse than the one recorded by changes in catch sizes. In the early days, too, longlines would have been more saturated with fish. Some individuals would therefore not have been caught, since no baited hooks would have been available to trap them, leading to an underestimate of fish stocks in the past. Furthermore, in the early days of longline fishing, a lot of fish were lost to sharks after they had been hooked. That is no longer a problem, because there are fewer sharks around now.
Dr. Myers and Dr. Worm argue that their work gives a correct baseline, which future management efforts must take into account. They believe the data support an idea current among marine biologists, that of the "shifting baseline". The notion is that people have failed to detect the massive changes which have happened in the ocean because they have been looking back only a relatively short time into the past. That matters because theory suggests that the maximum sustainable yield that can be cropped from a fishery comes when the biomass of a target species is about 50% of its original levels. Most fisheries are well below that, which is a bad way to do business. [br] The extinction of large prehistoric animals is noted to suggest that ______.
选项
A、large animals were vulnerable to the changing environment
B、small species survived as large animals disappeared
C、large sea animals may face the same threat today
D、slow-growing fish outlive fast-growing ones
答案
C
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3299998.html
相关试题推荐
Ifyou________tosomething,youmentionitinaveryindirectway,oryoujustb
BythetimeBobarrivesinBeijing,wehavealreadyarrivedherefortwodays.A、
Thenursegavemesomethingto________thepain.A、aggravateB、increaseC、augment
Shesearchedthefacesfortwobelovedones,butsomethingtoldhersoftlythat
Allofthepeopleinthelabwere________bythestrangeresultsoftheexperimen
Ifyouthoughtmultimediawassomethingtobeenjoyedintheprivacyofyour
[originaltext]Whenshefirstarrivedinthiscity,Ms.Allansharedaroomwith
[originaltext]Whenshefirstarrivedinthiscity,Ms.Allansharedaroomwith
[originaltext]Whenshefirstarrivedinthiscity,Ms.Allansharedaroomwith
Whenprehistoricmanarrivedinnewpartsoftheworld,somethingstrangehap
随机试题
Whohastakenstepstoresolvetheconflict?[originaltext]U.N.SecurityC
当可燃气体报警控制器有可燃气体报警信号、故障报警信号、屏蔽信号输入时,应向消防控
A.地西泮 B.硫喷妥钠 C.琥珀胆碱 D.哌替啶 E.肾上腺素治疗局麻
内部管理不良预警系统包括( )。A.质量管理预警 B.技术变化预警 C.设
感冒夹惊证的治疗应该在疏风解表基础上加用的方剂是()A.镇惊丸 B.保和
患者女,42岁。反复大量呕吐4天,尿少,伴恶心,乏力。查体:脉搏126次/分,血
商流费用包括()。A:市场分析费用 B:商品销售费用 C:谈判签订契约费用
关于评标委员会的表述,正确的是()。A.评标委员会成员的名单应当保密 B
填筑排水砂垫层施工前施工单位应做压实工艺性试验,确定主要工艺参数,并报()确认
《安全生产许可证条例》规定,除中央管理的建筑施工企业外,建筑施工企业安全生产许可
最新回复
(
0
)