There are more dolphins in captivity than ever before
In the seaside resort of Taiji in Japan, around 3,000 dolphins are hunted and killed for food each year.
Known as "drive hunting", the fishermen bang metal poles in the water, disturbing the dolphins' sonar and enabling them to drive the animals into shallow water where they can be caught.
At first unwilling to speak to the media, the handful of fishermen permitted to catch dolphins in Taiji reluctantly agreed to speak to reporter Paul Kenyon.
They insist their occupation is traditional and legal, and are enraged by the groups of international animal rights activists who travel to Japan to protest against the hunts.
One such protester, Ric O'Barry, a marine mammal specialist with One Voice, insists: "The dolphins have a brain larger than the human brain, so when they're being slaughtered like this they're aware... just like humans."
In a local bar, Paul shows the fishermen a research film on dolphin intelligence, but they dismiss the animals in the film as "highly-trained" and therefore more able to perform the tasks given to them.
Some dolphinarium scouts look for new performers at the drive hunts
Dolphin meat is a common sight on menus in Taiji, but food is not the only reason for drive hunting.
In 2003, 78 of the dolphins trapped in the hunts were used for dolphinarium shows and swim-with-dolphin programmes.
There are substantial rewards for dolphins employed by the increasingly-popular entertainment business; not for the hunters themselves, but for the industry's intermediaries - the groups who make money by buying the dolphins from the fishermen and selling them to dolphinariums for training.
It is estimated that "dolphin dealers" can sell one animal for up to $30,000 (£16,000). Paul confronts the head of one such intermediary organisation and puts it to him that the dealing business is actually the driving force behind the industry.
It also becomes apparent that there are international dealers. Footage of the hunts taken by Ric O'Barry show Westerners trying to buy dolphins from the fishermen in Taiji.
This astonishing evidence takes Paul further afield than the shores of Japan.
Producer/director/reporter: Paul Kenyon
Series producer: Sandy Smith
Executive producer: Karen O'Connor