Conservation efforts have helped boost the fortunes of the European bison, which at one time only survived in captivity, experts have said.

The bison, Europe’s largest land mammal, is one of more than two dozen species which have seen an improvement in their status in the latest update of the International Union for Conservation of Nature (IUCN) Red List of Threatened Species thanks to conservation work.

But 31 species have become extinct, including 15 fish species found in a lake in the Philippines and three different Central America frogs, it reveals.

And all of the world’s freshwater dolphin species are now threatened with extinction, the update shows.

The Red List now includes 128,918 species, of which 35,756 are threatened with extinction.

As a result of long-term conservation management, the wild population of European bison has increased from around 1,800 in 2003 to more than 6,200 in 2019, the experts said.

In the early 20th century bison only survived in captivity after being hunted to extinction in the wild, and were reintroduced in the 1950s.

There are currently 47 free-ranging European bison herds, with the largest subpopulations found in Poland, Belarus and Russia, but their groups are isolated from each other and confined to forests that do not make the best habitat.

With only eight herds large enough to be genetically viable in the long term, they remain reliant on conservation measures such as moving bison to better, more open habitats to help them, the IUCN said.

They were historically reintroduced mostly to forest habitats, where they cannot find enough food in winter, but when they move out into agricultural land they can come into conflict with farmers.

Dr Rafal Kowalczyk, co-author of the new assessment, said: “To reduce the conflict risk and the bison’s dependence on supplementary feeding, it will be important to create protected areas that include open meadows for them to graze.”

But the increase in numbers has allowed the species to be moved from the category of “vulnerable” to extinction to the less severe listing of “near threatened” in the latest Red List assessment.

Elsewhere on the Red List, the tucuxi, a small grey dolphin species in the Amazon river system which has been hit by getting caught in fishing gear, as well as the damming of rivers and pollution, has been moved from the category of data deficient to being assessed as endangered.

That means all the world’s freshwater river dolphins are now threatened with extinction, the experts said.

The lost shark, which was only formally described as a species last year, is listed as critically endangered, possibly extinct, as it was last recorded in 1934 and its home in the South China Sea has been heavily fished.

Some 15 species of fish endemic to Lake Lanao and its outlet in the Philippines are now extinct, while the remaining two are critically endangered, possibly extinct, as a result of a predator species being introduced, as well as overfishing and destructive fishing methods.

In addition to three Central American frogs being declared extinct, 22 species across Central and South America are listed as critically endangered, possibly extinct, mostly due to chytrid disease.

There is better news for some amphibian species, including the Oaxaca treefrog, which has moved from critically endangered to near-threatened thanks to conservation action by local communities in Mexico.

Almost half (45%) of the striking flowering plants in the protea family are threatened with extinction, while an assessment of oak trees reveals that almost a third (31%) of species are also under threat.

IUCN director-general Dr Bruno Oberle said: “The European bison and 25 other species recoveries documented in today’s IUCN Red List update demonstrate the power of conservation.

“Yet the growing list of extinct species is a stark reminder that conservation efforts must urgently expand.

“To tackle global threats such as unsustainable fisheries, land clearing for agriculture, and invasive species, conservation needs to happen around the world and be incorporated into all sectors of the economy.”