By Alex Kirby
BBC News Online environment correspondent
Some whales, dolphins and porpoises are now so endangered they could vanish within a decade, scientists say.
The warning comes from an international group of cetacean experts at IUCN-The World Conservation Union.
They say species like the baiji (the Yangtze River dolphin) are unlikely to last for another 10 years.
Other small cetaceans and several of the great whale species are almost as endangered, they believe.
The experts issue their warning in Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans.
The plan is the third of three written by IUCN's Cetacean Specialist Group (CSG) in the last 15 years.
Help for the overlooked
It lists the 86 recognised cetacean species, from the whales of the high seas to the small and increasingly seldom-seen freshwater species in southern Asia and Latin America.
A Ganges River dolphin: Endangered (Image: Brian D Smith)
Dr Randall Reeves, who chairs the CSG, said: "Some of the great whales such as the blue, humpback, sperm and right whales often receive a lot of attention.
"They are magnificent animals, and certainly important to the CSG's mission. The Group focuses, however, on smaller species, often lesser-known and in developing countries, that are particularly threatened with extinction."
The CSG says humans have not so far caused the extinction of any cetacean species, but it thinks that could change.
A former CSG chair, William Perrin, said: "It seems unlikely the baiji will still be around when the next action plan is formulated eight or 10 years from now."
The baiji, a freshwater dolphin now limited to the main channel of the Yangtze river in China, is considered the most endangered cetacean.
Monofilament nets are death to dolphins (Image: Brian D Smith)
From surveys in 1985 and 1986, the total population was estimated at around 300 animals. Between 1997 and 1999, extensive surveys sighted only 21-23 dolphins.
Other cetaceans thought at extreme risk are the vaquita (the Gulf of California porpoise) and several local populations of whales and dolphins, all classed on IUCN's Red List as critically endangered.
Other endangered cetaceans include northern hemisphere right whales, the blue whale, Hector's dolphin, and the Ganges/Indus River dolphins. Some species still awaiting formal assessment are known to be in serious danger of extinction.
William Perrin said: ""Some progress has been made, but... grave threats to the continued existence of many cetaceans still exist, and some threats are worsening.
North Atlantic right whale (Image: Noaa)
"Cetacean diversity, like all biodiversity worldwide, is crumbling, so we must redouble our efforts."
Threats to cetaceans include the deliberate killing of some species for food and predator control.
Animals die after becoming entangled in fishing gear, or colliding with vessels. Some species are targeted to supply the demand from aquaria for live animals.
Glimmers of hope
Fishing depletes food sources, coastal habitats are damaged by development, and new types of military sonar can apparently cause lethal damage to deep-diving cetaceans.
But the CSG sees some signs for hope. It says: "Several populations of southern right whales, humpbacks in many areas, grey whales in the eastern North Pacific, and blue whales in both the eastern North Pacific and central North Atlantic have begun to show signs of recovery."
The plan includes recommendations for action to protect some of the most threatened species. These include modifications to fishing methods that would benefit the baiji, vaquita, and Hector's dolphin.
Blue whale image courtesy of Dan Shapiro/US National Oceanic and Atmospheric Administration