This is the VOA Special English ENVIRONMENT REPORT.
Scientists in Canada say big ocean fish have almost disappeared from the world since the start of industrial fishing in the nineteen-fifties. The scientists found that populations of large fish like tuna, swordfish and cod have dropped by ninety percent in the past fifty years.
The study took ten years. The researchers gathered records from fishing businesses and governments around the world. The magazine Nature published the findings.
The scientists say the common method called longline fishing is especially damaging to populations of large fish. This method involves many fishing lines connected to one boat. These wires can be close to one-hundred kilometers long. They hold thousands of sharp metal hooks to catch fish.
Longline fishing is especially common in the Japanese fishing industry. Records showed that Japanese boats used to catch about ten fish for every one-hundred hooks. The study says longline fishing boats now might catch one fish per hundred hooks.
Modern methods also include the use of satellites and underwater radar to find fish.
The scientists say industrial fishing can destroy groups of fish much faster than in the past. The study suggests that whole populations can disappear almost completely from new fishing areas within ten to fifteen years.
Ransom Myers of Dalhousie University in Nova Scotia led the study with Boris Worm of Dalhousie and the University of Kiel in Germany. Mr. Worm says the destruction could lead to a complete re-organization of ocean life systems. Mr. Meyers says the decreased numbers of large fish is not the only worry. He says even populations that are able to reproduce do not get the chance to live long enough to grow as big as their ancestors. He says not only are there fewer big fish, they are smaller than those of the past.
American government scientists say even with the best efforts to protect fish populations, decreases are to be expected. Fishing industry groups say the study makes the situation seem worse than it is. They say programs are in place to help repopulate big fish where numbers are low. And they say there have already been some improvements.
Last year, many countries signed a declaration in South Africa to work toward the recovery of fishing areas by two-thousand-fifteen.
This VOA Special English ENVIRONMENT REPORT was written by Caty Weaver.