Our knowledge about the health of living dolphin and porpoise populations is sadly incomplete. Only five species have been determined to be "vulnerable" or "endangered", and most others are described as "insufficiently known." Too many times, we can say only that the "total population is unknown" or the "number killed is unknown" or "much more research is necessary." The grave danger is that some unique and fascinating dolphin species will be gone before detailed research and population censuses can be carried out.

Urgent action is needed to avert the deaths of hundreds of thousands of dolphins and porpoises that are accidentally killed every year. Some years, the figure has surpassed half a million worldwide - all because of human activities. This is more than 10 times the number of large whales that were slaughtered in the early 1930s, the worst years of whaling.

Dolphins may be dying because of pollution from dumping at sea, oil spills and farm pesticides and other chemical runoff that enter the rivers, particularly in the Mediterranean and off the east coast of the United States, dolphins have been dying by the hundreds, then washing ashore, victims of explained viruses or weakened immune systems that may have been caused by pollution. In some cases, food poisoning from red-tide organisms may have been the cause. But some scientists believe that pollution from PCBs, DDT and other contaminants is responsible. The contaminants are picked up in plankton, then they move to fish and other plankton-eaters and, finally, to dolphins and porpoises. The contaminants might not cause immediate death but, rather, a weakening of the immune system that leaves the animals more susceptible to disease.

Dolphins and porpoises are commonly killed in encounters with fishermen in every ocean. Before the 1970s, fishermen in the North Pacific off British Columbia and Washington State and in the North Atlantic off Iceland shot orcas that they believed were scaring away or taking "their" fish. Fishermen in Japan and other places, angry that dolphins "steal" fish off their hooks or frighten fish away, drive great herd of dolphins into the shallows, killing them. Bottlenose dolphins, false killer whales, Risso's dolphins and Pacific white-sided dolphins are among the victims. Fishermen either sell them for meat and fertilizer or leave them to rot.

Some individual dolphins do learn to follow fishermen for a "free" lunch, yet such behaviour is uncommon, and it certainly does not threaten fish species. No dolphin or porpoise, no sea mammal, can compete with modern fishing fleets.

The biggest threat to dolphins is the fisherman's net. Nets sometimes kill dolphins accidentally, while other times, fishermen "set" on dolphins. In the eastern tropical Pacific and in other seas, tuna fishermen follow dolphins to locate schools of tuna. These fishermen are mainly on the lookout for spotted dolphins, but they also watch for the spinner, common and Fraser's dolphins that live in this part of the open Pacific and often associate with yellowfin tuna. The fishermen set their purse seines around the herd of dolphins, catching the dolphins and, down below, the commercially valuable tuna.

In the 1960s and 1970s, between 200,000 and 500,000 dolphins a year became entangled and suffocated in tuna nets. It was a staggering number and one that resulted in the Marine Mammal Protection Act, which was passed in the United States in 1972 to protect dolphins. Some nets were redesigned with escape panels so that dolphins could swim free. But most of the tuna boats were sold to other countries, which simply passed along the problem.

By the early 1980s, an estimated 80 percent of the spinner dolphins in the eastern Pacific had been killed. Environmental groups in Canada, the United States and Britain asked people to support dolphins by refusing to eat tuna. This consumer boycott helped create "dolphin-safe tuna" - the marketing of tuna that have been caught on lines or by methods which ensure that no dolphins are killed. By the early 1990s, dolphin kills by U.S. fishermen were down to fewer than 10,000 per year, and most U.S. fishermen had moved away from the eastern tropical Pacific. But fishermen from other countries continue to use dolphins to catch tuna in the eastern tropical Pacific and, to an unknown extent, in other areas of the world oceans as well.

Besides dying in tuna nets, dolphins are killed in every part of the world ocean by gill nets, trawls and even long-line fishing. The most indiscriminate killers - the new ocean drift nets - are up to 50 kilometers long. Made of strong nylon monofilament that dolphins cannot always detect, these nets are called "walls of death" by environmentalists. Tens of thousands of dolphins and porpoises are caught in drift nets every year, as are many noncommercial species of fish, birds, turtles and other marine mammals. Most of these go to waste, however, when drift-net fishermen haul in their nets, keeping the tuna and discarding the rest.

Some countries have banned these nets within their own territorial waters, up to 325 kilometers offshore. It's a start, but nets still crisscross the open seas, where neither government nor reason rules. In 1991, however, the United Nations General Assembly called for a global moratorium on long high-seas drift nets. UN resolutions are not binding, but Japan, Taiwan and South Korea - the three main drift-netting countries - agreed to reduce their operations immediately and to stop them completely by the end of 1993.

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