Polar bears and hippos have joined the ranks of threatened species, along with a third of amphibians and a quarter of mammals and coniferous plants, according to the World Conservation Union.

The conservation group's Red List of endangered species found that 16,119 species are at the highest levels of extinction threat, equivalent to nearly 40% of all species in its survey.

Fish are in particular danger, with more than half of freshwater species in the Mediterranean basin facing threats and formerly common ocean fish such as skate disappearing.

The World Conservation Union, known by the acronym IUCN, found that more than 500 species had been added to the ranks of those classified as endangered, critically endangered or vulnerable since 2004 - a rise of 3%.

There are estimated to be around 15m species in the world, although only around 12% of that number have ever been classified by scientists and the Red List examines 40,000 species.

At present, animals are believed to be going extinct at 100 to 1,000 times the usual rate, leading many researchers to claim that we are in the midst of a mass extinction event faster than that which wiped out the dinosaurs.

IUCN director general Achim Steiner said that there was no slackening in the rate of global extinctions, and warned that tackling the problem would require governments, civil society groups and businesses to work together with environmentalists.

"Biodiversity loss is increasing, not slowing down," he said. "Reversing this trend is possible [but] biodiversity cannot be saved by environmentalists alone - it must become the responsibility of everyone with the power and resources to act."

The Arctic Climate Impact Assessment said in 2004 that Polar Bears would be extinct within 100 years, and some scientists believe that they could disappear within 25 years. The IUCN predicted a more conservative decline of 30% in the next 45 years.

The report also said that civil breakdown in the Democratic Republic of Congo had led to a catastrophic decline in hippo populations, with the country's 30,000-strong herds losing 95% of their numbers to poaching and ivory hunting since 1994.

The list showed 784 species as extinct and 65 as existing only in captivity. Other particularly threatened animals included the dama gazelle of the Sahara, the goitred gazelle of central Asia, the Angel shark of the North Sea, the West African pygmy hippo, and a species of trout from Lake Malawi.

Two carp species from Turkey and Croatia were listed as extinct and one in eight classified bird species were endangered or vulnerable, along with a third of dragonflies. The Mediterranean herbs bugloss and centuary were listed as critically endangered.

The IUCN said that people were responsible for the majority of extinctions, via habitat destruction or degradation. Invasive species, overhunting, pollution and unsustainable harvesting were also mentioned as major causes of threats, along with climate change.

A 2004 report by the University of Leeds found that a quarter of land animals and plants could be driven to extinction by global warming.

However, the IUCN did report some success stories. White-tailed eagles have been downlisted from the "near threatened" category to "least concern" after anti-poaching and pollution enforcement measures led to a doubling of its population in Europe during the 1990s.

It also said that the future of the Indian vulture looked positive despite a 97% population decline leading to it being listed as critically endangered in 2002. A veterinary drug responsible for accidentally poisoning the vultures has since been banned in India.