Four dolphins have escaped from an aquatic zoo resort in Japan, near to where dozens are killed during annual hunts.

The creatures were able to swim away after the nets separating their pens from the ocean were slashed open at the DolphinBase centre in Taiji.

Staff from the park said the animals were between three and five years old, and had been trained in small enclosed pools along the coastline.

Taiji 'cove' dolphin hunt

Every year fishermen from Taiji shepherd scores of dolphins into secluded bays and slaughter them for sport, a practice that has been widely condemned by activists around the world.

At DolphinBase captured dolphins are exhibited in hourly shows, and tourists are invited to swim and interact with them. Staff said it was likely campaigners had cut the nets to free the dolphins.

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“We are enraged by this heinous act which can easily lead to the dolphins dying,” the centre said in a blog post. “It was a very optimistic, selfish and irresponsible act by someone without any knowledge, and we feel it risks the lives of these dolphins in a real way.”

Since their escape, three of the four dolphins have been returned to their pens. A spokesperson from Taiji Police said an investigation had been launched to find out who cut the nets.

The annual dolphin hunt first gained global attention in 2009 when it became the subject of the documentary The Cove, which won an Oscar the following year.