Japan’s annual dolphin hunt, a practice fiercely opposed by animal rights activists around the world, has started in the small coastal town of Taiji.

The hunting season kicked off in the town in Wakayama Prefecture on Sunday, with 12 boats reportedly setting off at 5am, before returning empty handed later in the day.

The practice, which will continue for around six months, sees fishermen herding dolphins and small whales into a cove with a net, before they are either slaughtered with knives or sold to aquariums.

The town’s annual dolphin hunt was cast into the global spotlight after the 2009 Oscar-winning documentary The Cove captured graphic scenes of the slaughter, inspiring a growing number of activists visiting the town to oppose the practice.

Japan’s maritime hunting policies have long been at odds with the international community. The new dolphin season kicked off just months after Japan officially left the International Whaling Commission on June 30, paving the way for the resumption of commercial whaling in July for the first time in 31 years.