High seas drift nets, made of non-biodegradeable plastic or nylon, can be up to 60km (37mls) in length. They are suspended vertically in the water with floats attached to the top and weights fixed to the bottom. Once set, the nets are then allowed to drift with the wind and currents, indicriminately entangling any living creature that swims into them, including marine mammals.

Their use has been reported in virtually every ocean, especially the Pacific, Atlantic and Indian Oceans, and in many seas including the Mediterranean.

In the North Pacific alone, more than 32,000km (20,000mls) of net are set each night, which means that over the course of the year, a staggering one and a half million kilometres (1 million nautical mls) of net are deployed there in the course of a year.

Because high seas drift net fisheries are unregulated and conducted far out at sea, it is impossible to say how many marine mammals they kill annually. However, a few examples serve to demonstrate the destruction caused by this form of fishery.

In early 1989, a trial use of drift nets to catch skipjack tuna in South Pacific waters killed an average of four and a half marine mammals in every 'set' - one marine mammal for every 10 tuna caught. The results of the trial prompted the State of Yap, which had initiated the experiment, to terminate the fishery permanently.

In 1986, one Japanese squid boat in the Pacific was observed to kill 59 small cetaceans in just 30 sets - a rate of almost two per set. Extrapolation from figures such as these is risky, but with 50,000-60,000 sets made by these fisheries annually, it is clear that the number of dolphins and porpoises dying each year in drift nets around the world could very well reach a six figure number.

It is believed that the small cetacean species most commonly caught are the Dall's porpoise, and the northern right whale, Pacific white-sided and common dolphins. Tens of thousands of Dall's porpoises are known to be killed by Japanese squid fisheries each year and in the Mediterranean at least 2,000 striped dolphins die annually in the Italian swordfish and bonito drift net fisheries.

Drift nets often break loose in the course of operations. They sail through the oceans, 'ghost fishing', until under the weight of the marine creatures they have ensnared, they sink to the bottom of the ocean. It is estimated that drift net fleets leave approximately 1,000km (600mls) of these 'ghost nets' floating in the North Pacific annually. At present rates of fishing, by the year 2000 there will be enough of this abandoned net to stretch one-third of the way around the world.

Many nations, such as New zealand, Australia and a number of South Pacific states, are vigorously opposed to the use of such fishing technology by foreign fleets in their waters because of the disruption they cause to the marine ecosystem. In june 1989, the South Pacific Forum issued the Tarawa Declaration, which called for an end to all drift net fishing in the Forum areas and this was followed a few months later by a resolution from the South Pacific Commission calling for an immediate ban on drift net fishing.

When it became known that drift net fleets in the North Pacific were intercepting large shoals of salmon bound for spawning streams in the US, as well as huge numbers of marine mammals and birds, the United States reached agreements with Taiwan, Japan and South Korea, requiring that they allow US observers on their drift net vessels or face an embargo of their products. Unfortunately, these agreements are very weak as there are, for example, only 14 American observers for a Japanese fleet of over 500 vessels.

In December 1989, the United Nations General Assembly passed a resolution which prohibited further expansion of drift net activities and called for their provisional phase-out in the South Pacific by 30 June, 1991 and throughout the rest of the world by 1992. This 'provisional moratorium' would still allow the use of drift nets of research showed that their impact could be limited through the adoption of 'conservation and management programmes.' At present [1990], this research will be restricted to reports, from a limited number of vessels, carried out by observers appointed by the drift netting nations themselves. Conservationists argue that the indiscriminate nature of drift netting is such that it can never be properly managed, and should be banned.

Such is the determination of some nations to act against the effects of drift net fisheries that they have banned large-scale drift nets completely from their waters. New Zealand passed a law in 1989 making it an offense for ships that use drift nets in any sea or ocean, any any ships supplying drift netters, to enter New Zealand waters. Other countries are now instituting similar measures.

Ironically, even Japan - which has one of the largest drift net fishing operations in the world - has banned large-scale drift nets deom its own waters because of the impact they have had on the ecosystem of its own Exclusive Economic Zone (EEZ).

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