Big ocean(海洋)fish have almost disappeared from the world since the start of business fishing in the 1950’s．The scientists found that the number of large fish has dropped by 90 percent in the past fifty years．The study took ten years．The researchers collected records from fishing business and governments around the world．The magazine Nature published the findings．
The scientists say the common way called longline fishing is especially harmful to large fish．This way includes many fishing lines that are connected to one boat．If these lines are joined together，they can reach one hundred kilometers．They hold thousands of sharp metal hooks to catch fish．Longline fishing is especially common in the Japanese fishing industry．Records show that Japanese boats used to catch about ten fish for every hundred hooks．The study says longline fishing boats now might catch one fish per hundred hooks．
The scientists say business fishing can destroy groups of fish much faster than in the past．The study suggests that large fish can disappear almost completely from new fishing areas within ten to fifteen years．Ocean life system could be destroyed．
It’s not the only worry that the number of large fish is becoming smaller and smaller．What’s worse．they are smaller in size than their ancestors(祖先)．

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句型转换。