The world's oceans, seas, and coastal areas are an essential component of the global life support system. But like the atmosphere, oceans have long been used for disposal of human wastes.
Refuse from ships, sewage from cities, and even nuclear wastes have been dumped haphazardly at sea for decades. Spills of oil and other pollutants have added to the problem; the UN reports that about 600,000 tons of oil enter the oceans each year as a result of normal shipping operations.
The trends of the past 20 years, according to the World Resources Institute in Washington, show increasing coastal pollution, accelerated destruction of coastal marine habitats, and, in many areas, a declining catch of marine fish species that have been affected by overfishing and pollution.
For the first time in history, stocks of most marine-fish species are now being fully exploited. At present, fisheries account for about 16 percent of the total animal-protein consumption in the world, about the same as beef and pork. The marine-fish catch in 1990 was 84.2 million tons - a 35 percent increase over the 1980 catch and more than a fourfold increase since 1950. In eight of the world's 17 ocean fisheries, the amount of fish caught exceeded the lower range of the estimated sustainable catch.
Increasing pollution in coastal waters and destruction of coastal estuaries, which provide reproduction grounds for 90 percent of the world's marine catch, are also degrading the fisheries. Expanding the catch for an expanding population will be difficult; it may take years of natural-stock rehabilitation just to maintain current production levels.
Marine pollution-control efforts have shown positive results in a few areas. But despite years of effort, only a small fraction of the world's waste water is treated. And new surveys show that more than 50 percent of nitrogen, phosphorus, and sediment pollution is a result of runoff from cities, farms, and logging and mining operations, not from sewage discharge.
At the Fourth Session of the Preparatory Committee of the UN Conference on Environment and Development in early April, delegates agreed to strengthen existing global agreements aimed at controlling land-based sources of marine pollution - fertilizers, pesticides, and the like, which account for more than two-thirds of ocean pollution. They have also agreed to improve collection of data on both marine resources and damage from pollution.
The outstanding ocean issue for the Earth Summit is how to regulate fishing rights for species that migrate between exclusive national economic zones and international waters. Canada has been particularly concerned about overfishing by other nations off Newfoundland. Coastal states have exclusive jurisdiction over the fisheries that exist within 200 miles of their shores.