Rainbow warriors in the ocean killing fields

Eye witness: Greenpeace - Trying to save the Cornish dolphins

The shipping news was unpromising: "Low, south to south-west, force five to seven, increasing occasionally gale eight." Outside the warmth of the bridge, three scientists stand at their stations wrapped in oilskins, their eyes peeled, binoculars at the ready.

The vessel, a converted steam trawler, bounces along the white horses of the open seas. She is the Rainbow Warrior II, the emblematic flagship of Greenpeace, and once again she is sending out a conservation message to the world.

But this is not a tale of environmental apocalypse from a faraway tropical paradise. The Rainbow Warrior's present mission is closer to home: she is monitoring what environmentalists describe as the "killing season" of whales and dolphins off the west coast of England.

Winter heralds the main season for mid-water trawling of sea bass, but the gill nets used by fishermen catch not only fish but also by-catch cetaceans, the collective name for dolphins, porpoises and whales. More than 120 dead whales and dolphins were washed up on West Country beaches between January and April, according to the Whale and Dolphin Conservation Society (WDCS), which believes hundreds more are killed but their carcasses never found.

It is a cruel death. Trapped in the nets, the dolphins close their blowholes rather than drown and so instead suffocate. The tight nylon fishing nets leave deep cuts and carcasses have been deliberately mutilated by fishermen removing them from the nets.

Greenpeace has provided the Rainbow Warrior and her crew to assist the WDCS in a six-week population study of western Britain's coastal waters, from Cardigan Bay to Poole. More than 20 species of cetacean can be found in UK waters, including bottlenose dolphins, rarer Risso's dolphins and harbour porpoises. Due to the elusive lifestyles of the cetaceans and a lack of dedicated research, the full consequences of the threat from the intensive fisheries is not well understood. The message, though, is a stark one: unless action is taken, the much loved spectacle of dolphins playing in local waters could be lost within a few decades.

As we trundle along the Cornish coast towards Plymouth, the waves grow larger. We look for the distinctive dorsal fins of dolphins and the flukes of whales. Acoustic equipment is set up to track the animals by hydrophones. Dolphins squeal, I learn, while orcas can be individually identified by their speech – and even by dialect.

At Plymouth, the plan is to head due south and out to sea for perhaps 30 miles, following random routes to find a snapshot of the moving patterns of the animals. But the barometer is plunging and it is time to call it a day.

"The weather is right on the limit," said Derek Nicholls, the ship's captain. "You can spot dolphins in similar weather but even no sightings can be useful." Mr Nicholls was at the helm in 1995 when French commandos jumped on board as the second Warrior sailed to the Pacific to protest against nuclear testing. "I was really incensed by the French government," he recalls. "Conservation matters because I have a daughter and I want her to be able to see the things I've seen. This is entirely compatible with the work we do. The stuff people see on television tends to be the last resort."

Below decks in the mess, John Wills, Greenpeace's logistics co-ordinator, elaborates on the group's evolving tactics. "Perhaps we have been perceived as people who just say 'no'," he said. "We are doing more positive work. It isn't enough just to say dolphin populations are decreasing. We have to provide solutions."

Techniques being explored to reduce by-catch include the addition of sonar "pingers" to nets, so that the cetaceans are alerted to the obstacles. Meanwhile, results from the project will be used in developing marine Special Areas of Conservation. "It's about distribution and abundance," said Jessica Feghali, conservation officer with WDCS. "This is an important step on the ladder to protect these species."

Some conservationists believe the next phase should see observer boats equipped with cameras to shadow the big trawlers. Doug Beveridge of the National Federation of Fishermen's Organisations said such an approach could polarise opinion. "Fishermen are far more in tune with the environment than some conservationists," he said. "Fishermen don't want to see any animals suffer unnecessarily. On a practical level they want to avoid entangling animals because that damages their nets."

Few West Country fishermen work in the sea bass industry. The technology for catching bass with gill nets was developed by the French, whose vessels continue to operate in the Channel. Jim Portus of the South Western Fish Producer Organisation believes the will exists to achieve a sustainable solution. "This is a commercial business," he said. "But fishermen don't want to engage in destructive methods. They don't want to be the ones who catch the last fish. Concern for the environment is not the exclusive domain of Greenpeace. Fishermen have consciences too."