Japan's hunting of dolphins, smaller whales and porpoises is threatening some species with extinction in its coastal waters, a report by a British environmental group has said.
The Environmental Investigation Agency (EIA) report says that more than a million such creatures have been killed in Japanese hunts in the past 70 years.
It says that each year thousands are killed despite conservation concerns.
The Japanese government has not commented on the report.
But it has consistently defended its coastal whaling as a longstanding tradition, a source of livelihood and necessary for scientific research.
The government has also argued that small cetaceans should be excluded from the International Convention on Whaling.
The BBC's Rupert Wingfield-Hayes in Tokyo says that the Japanese practice of driving many dolphins and porpoises onto beaches to be slaughtered has drawn international condemnation.
The EIA says that it is also unsustainable, and a danger to human health. Studies have found high levels of mercury and industrial chemicals like PCBs in dolphin and porpoise meat.
One study found people living in one dolphin-eating community in central Japan have mercury levels five times higher than normal.
"A comprehensive analysis of the available scientific data demonstrates unequivocally that there are grave concerns regarding the sustainability of these hunts," the EIA report says.
It goes on to accuse the government of "displaying a lack of responsibility" in ensuring the sustainability of small cetacean populations in Japanese waters - warning that its annual quota of 16,000 dolphins is far too high.
The EIA says that the quota is based on 20-year-old data and that dolphin populations are much lower now.
The conservation status of each species varies, the report says, depending on its range and hunting practices.
Catch limits for Dall's porpoises are 4.7-4.8 times higher than the safe threshold, it claims.
For the striped dolphin, once the mainstay of the industry but now endangered and disappearing from some areas, catches have dropped from more than 1,800 in the 1980s to about 100 today.
Our correspondent says that anyone who has seen the documentary The Cove will know how controversial Japan's annual dolphin hunt can be.
Hundreds of animals are driven into a bay where men jump into the water and cut their throats, turning the sea red.