A trade ban is looming for two endangered otter species after 100 countries voted to increase protections following a social media-fuelled craze for acquiring the mammals as pets.

A majority of parties to the Convention on International Trade in Endangered Species (Cites) voted to place the smooth-coated otter on the treaty’s most endangered list on Sunday. On Monday, they voted to do the same for the Asian small-clawed otter.

Conservationists hailed the vote, insisting a trade ban was vital for the survival of the two species, whose numbers in the wild have fallen by at least 30% in the past 30 years.

This decline is believed to have accelerated significantly in recent years with a fad in Asia – and Japan in particular – of keeping otters as pets.

Matt Collis, the policy chief at the International Fund for Animal Welfare, said: “This is an important conservation victory.”

He said he hoped the move would “send an important message to unscrupulous traders, add further trade controls and enhance scrutiny of captive-breeding operations”.

The votes were to move the two otter species from Cites appendix II, where international trade must be regulated and monitored for sustainability, to appendix I, where all international trade is banned. They still need to be approved in a plenary session before the 12-day conference in Geneva wraps up on Wednesday.

Sumanth Bindumadhav of Humane Society International said he hoped the move would “send an important and timely warning, not least to online and social media audiences, that these are imperilled species and that trade in them is harmful to their welfare and their overall species survival”.

All Asian otter species have long been listed as vulnerable or endangered after decades of shrinking habitats and illegal trade in their pelts. But conservationists say the recent surge in social media hype around the animals has caused such frenzied demand for baby otters in Asia that it could drive entire species towards extinction.

To meet the growing demand, hunters and fishermen, especially in Indonesia and Thailand, are increasingly killing adult otters and snatching the babies, which are caged and shipped off to become exotic pets.

The main destination is Japan, where one otter pup can fetch up to $10,000 (£8,200). Several “otter cafes” have also popped up in the country, with patrons urged to buy small pieces of food to feed the caged mammals.

Countries also voted on Monday to move the Indian star tortoise – another species being endangered by the exotic pet trade – to appendix I.