It wasn’t always so. Back in the sixties O’Barry was one of the most famous animal handlers in the world, being the principal trainer and dolphin handler on the popular television series Flipper. It was through his extended contact with Kathy, one of five bottlenoses who portrayed the show’s eponymous hero, that he came to regard dolphins as highly intelligent, cognizant beings (‘self aware’ as he puts it). Following the show’s cancellation Kathy died after months of isolation in a concrete tank, and it was then that O’Barry decided to devote the rest of his life to ensuring the liberty of the very animals he had once helped capture. He was arrested two days later for attempting to free a captive dolphin from a sea pen off the island of Bimini, and has been an active crusader for the rights of these much-loved creatures ever since.

With the aid of director Louie Psihoyos, a longtime National Geographic photographer, O’Barry’s principle aim in The Cove is to draw attention to the widespread herding and slaughter of dolphins in the waters surrounding the Japanese town of Taiji. Using a technique known as drive hunting, boatloads of Japanese fisherman surround swarms of migrating dolphins and herd them into the coves that dot the local coastline. They then return the following morning to round up a few show-quality females, which are highly desired by operators of dolphin shows around the world and can fetch upwards of $150,000 each. The remaining dolphins, many thousands each season, are then fenced together and stabbed to death by fisherman wielding spiked poles, harpoons and knives. It is not a quick or humane process; for several minutes the sea churns as the dolphins thrash in agony. It is a sight that once seen is difficult to forget. When the carnage finally ends the entire cove runs red with the blood of the slaughtered animals, which are then unceremoniously towed away in order to be sold at fish markets around Japan. It’s a haunting, horrifying and deeply disturbing spectacle. There are other ethical reasons for objecting to the mass culling of cetaceans; due to a semantic loophole dolphin meat is regularly passed off as whale in Japanese supermarkets. The main problem with this deception is that the meat of small cetaceans like bottlenose dolphins has been found to contain many times the levels of mercury considered safe for human consumption. Thus not only are Japanese consumers unwittingly contributing to this secretive and perennial bloodshed; they are also unknowingly poisoning themselves and their families.

The Japanese government and the local fishermen whose livelihoods depend on the dolphin slaughters zealously protect the area surrounding the infamous cove where the killings take place. Fences, barbed wire and patrols of stony-faced locals form a nearly impenetrable barrier between the township and the captive mammals. In addition O’Barry and his ilk are thoroughly unwelcome in fishing and whaling communities, facing constant harassment from police, officials and local residents. In the film’s opening scene in which the aged activist drives around Taiji and introduces its main points of interest, he wears a face mask and hunches in the driver’s seat so as to give the impression to passers-by of being an elderly Japanese. Occurring as it does so early in the piece one’s initial reaction is to dismiss him as an overly suspicious old kook. But this is a $2 billion dollar a year industry, and its main proponents do not take kindly to the interference of environmentalists. O’Barry’s paranoia is, it seems, justified; several of his colleagues over the years have been murdered for their participation in protest efforts, including conservationist Jane Tipson, who was killed in St Lucia in 2003 and Jenny May, a colleague of O’Barry’s, who was followed onto an isolated beach by disgruntled Russian dolphin traffickers and strangled with her own belt.

Needless to say, footage of the Taiji slaughters has never previously been captured on film. In order to record the dolphin hunts O’Barry and Psihoyos recruited a crack squad of divers, scientists and activists, smuggling caseloads of specially designed cameras and microphones into their Taiji hotel rooms. Then the mission turns into something out of a spy film; over a period of several nights the ragtag crew sneak up into the hills surrounding the cove, laying down their cleverly disguised audiovisual equipment before regrouping and sneaking back to their digs as discreetly as possible. They approach the task with all the planning and tactical nous of a covert operations task force, utilising radio communication, thermal cameras, night vision goggles and getaway cars. Their efforts inevitably attract the attention of hotel staff and the local police, and the ensuing game of cat and mouse is one of the most thrilling aspects of this deeply engaging film. The resultant footage by no means makes for pleasant viewing, but this audacious documentary stands as one of the most shocking, not to mention compelling, environmental wake-up calls of recent memory.

The fishermen of Taiji made some modest concessions in the wake of the outrage generated by The Cove. They delayed the onset of the 2009 dolphin hunting season by one week, and as a further PR measure released some of the dolphins captured on the first day of hunting. Unfortunately however these actions were nothing more than a half-hearted publicity measure, and recent reports by O’Barry and others who have returned to Taiji confirm the killing of dolphins and whales continues unabated in the region.

Guerrilla filmmaking of the highest calibre, The Cove is not an easy film to sit through. Many of its scenes of cruelty and corruption invoke strong reactions of anger, and you probably won’t be booking a family trip to SeaWorld anytime after having seen it. Nonetheless this important and compelling documentary deserves to be viewed by as wide an audience as possible; hopefully it makes a difference.