Moscow (AFP) - A young beluga whale looks down as it is winched in a net onto the deck of a rusty Russian ship moored at a far-eastern port.

"Don't forget us, bitch!" shouts one of its captors onboard the ship as the animal is deposited next to three more belugas and rows of other sea mammals such as seals.

The grim footage -- aired in a recent Russian documentary -- shines a spotlight on a murky and poorly regulated trade in marine mammals that has made the country the biggest supplier of some species to aquariums across the globe.

Activists documented squalid conditions and dead beluga whales being hastily buried as traders exploited loopholes in legislation to turn a lucrative profit.

"We started making a film about aquariums, but I couldn't imagine such a huge business behind them, a huge corrupt system," said Gayane Petrosyan, who directed the film "Born Free" that premiered earlier this year.

While many countries around the world are phasing out the use dolphins for entertainment, China's industry is expanding and Russian animals are its star performers.

"The animals are treated as a commodity," Petrosyan said.

- Loopholes -

Officially Russia has exported 91 live marine mammals -- including seals, whales and dolphins -- since the beginning of 2016, 84 of which went to China, according to available customs figures.

Each year, the government permits traders to catch about 10 orcas and 150 beluga whales for zoos and oceanariums, said Dmitry Glazov, deputy chairman of Russia's Marine Mammal Council of scientists.

Permits for orcas, which fetch at least a million dollars each, are especially in demand.

While these numbers may sound low, activists believe the true figure is higher as fishermen abuse quotas meant to cover animals captured for educational or scientific purposes to export them commercially.

"If you catch an orca for education and cultural purposes in Russia and then sell it to China for those purposes, that's against the law," said lawyer Maxim Krupsky, who helps scientists opposing the trade.

- Population fears -

While neither orcas or belugas are listed as globally endangered animals, Russian scientists say that the lack of oversight in the trade and recent research means they are left in the dark over the numbers remaining in their waters.

"For many marine mammal species, it's not even clear how many animals there are, there have been no studies since the Soviet times," academic Glazov said.

A rough headcount in 2010 suggested there are two separate populations of beluga whales in the Russian Far East, and it would be sustainable to only catch 15 annually from each group, he said.

In reality, hunters focus on one group in the Sea of Okhotsk, north of Japan, grabbing as many as 80 animals in a single season and especially going after the juvenile females most important for the population's reproduction.

And as the animals are caught for "education" rather than commercial purposes, the government is not even getting any money in taxes from their sales, Glazov added.

Glazov said that the controversy resulted in an unofficial halt on live catch in 2016, but this year the government has allowed it again.

- Orca shows -

Whale and dolphin species like belugas and orcas are highly intelligent mammals who travel large distances and have complex societies. Unlike other animals, they are believed to live shorter lives in captivity.

International controversies surrounding their wellbeing in captivity as well as several killings of trainers by orcas, also known as killer whales, have put public pressure on parks like SeaWorld in the US, which announced it would stop keeping them last year.

In China however, new parks are opening up. Nine Russian orcas were unveiled this year in Chimelong Ocean Kingdom park, and at least two more entertainment facilities are opening over the next few years that promise shows featuring orcas.

All orcas caught in Russia come from the less numerous mammal-eating killer whale variety, rather than the fish-eating one, said Erich Hoyt, a research fellow with the Whale and Dolphin Conservation and co-director of the Far East Russia Orca Project.

Hoyt estimated the number of mammal-eating orcas as "probably in the low hundreds" in the Russian Far East.

"There is a risk that live catch will significantly erode the Russian orca populations," he said.

Glazov agreed that the practice should be stopped for all marine mammals in Russia.

"Until we know their numbers, there should be a moratorium on catching them," he said.