The vaquita, a diminutive Mexican porpoise feared near-extinct, made a big splash at a world whaling meeting Tuesday with pleas to arrest illegal fishing to prevent its extermination.

Sometimes referred to as Mexico's "panda of the sea", there were a mere 59 known vaquitas by the end of last year, according to reports to the International Whaling Commission (IWC).

Then in March, three were found dead in fishing nets.

"The situation of the vaquita is now in its critical phase," Justin Cooke of the International Union for Conservation of Nature (IUCN) told delegates to the IWC's 66th meeting in Portoroz, Slovenia.

"The numbers have further declined from about 100 animals when we discussed it in this room two years ago, to less than 60 now.

"If the decline is not stopped then by the time we next discuss it... in two years' time, it will be already too late to save the species."

The commission was discussing an "emergency" proposal by the United States to save the world's most threatened cetacean -- the group of whales, dolphins and porpoises.

The vaquita is the smallest of all the porpoises, which are similar to dolphins but tend to have shorter beaks and more rounded bodies.

They perish in nets used to illegally catch totoaba, large fish whose swim bladders -- organs used to control buoyancy -- are believed in China to hold medicinal powers.

Totoabas, which share their habitat with vaquitas, are endangered too.

- Extinction imminent, 'preventable' -

Vaquitas are grey-coloured porpoises with prominent black lines around their eyes and lips. They grow to about 55 kiloss (120 pounds) and 1.5 metres (five feet) in length.

Found only in the upper Gulf of California, they are listed as "critically endangered" by the IUCN, which keeps a "Red List" of animal species at risk.

Vaquitas drown when they get entangled in gillnets, vertical sheets of netting used to catch fish, and cannot surface to breathe.

First discovered as a species only in 1958, vaquita numbers have plummeted by 92 percent from 1997 to 2005, scientists say.

Thought to have numbered 567 in 1997 and 245 in 2008, their population shrank by 80 percent in the short period from 2011 to 2015, according to the IWC's scientific committee.

"The choice is simple and stark: either gillnetting in the Upper Gulf ends or the vaquita will be gone," the committee said in its latest report in June.

The proposed US resolution, backed by the European Union and others, calls for a temporary gillnet ban imposed by Mexico in the vaquita's territory to be made permanent, and policed effectively.

It also urges IWC members to assist Mexico with funding and technical expertise to enforce the ban, to compensate affected fishers, and replacing outdated fishing gear with safe alternatives.

Mexico supported the proposal.

Efforts must also be made to dampen consumer demand, conservationists say -- though that may take too long.

"A surge in swim bladder trade is being driven by speculators and criminal groups attracted to rapidly rising totoaba swim bladder prices," said Clare Perry of the Environmental Investigation Agency.

A big one can fetch $50,000 (46,000 euros), she said.

There were groans from some delegates when representatives of countries including Japan, Russia and commercial whaling nation Iceland, argued that small cetaceans such as vaquitas did not fall under the jurisdiction of the IWC.

The matter was held over for negotiators to seek a consensus position to be adopted, failing which the US-led proposal will be put to a vote.

Elusive by nature, the vaquita is difficult to observe. Little is known about their reproductive life and longevity.

Females are believed to have a single calf every two years or more, according to conservation group WWF.

"This imminent extinction is preventable," warned Cooke. "If we don't prevent it, it will be our collective failure."