A six-year lion survey across 11 African nations has ended with some sobering results: The West African lion is facing extinction across the entirety of its range.

Lions in the West Africa region once held a comfortable position the territory, ranging continuously from Senegal to Nigeria. But a new report by the big cat conservation organization Panthera reveals there are only about 250 adult lions in West Africa.

The remaining West African lions are "restricted to four isolated and severely imperiled populations," Panthera said in a statement. "Only one of those populations contains more than 50 lions."

According to the International Union for the Conservation of Nature (IUCN), lion populations of 50 or greater are "necessary to conserve genetic diversity and avoid inbreeding."

"When we set out in 2006 to survey all the lions of West Africa, the best reports suggested they still survived in 21 protected areas. We surveyed all of them, representing the best remaining lion habitat in West Africa," said Philipp Henschel, Panthera's Lion Program Survey Coordinator and co-author of a paper detailing the research in the journal PLOS One.

"Our results came as a complete shock; all but a few of the areas we surveyed were basically paper parks, having neither management budgets nor patrol staff, and had lost all their lions and other iconic large mammals," Henschel said.

The survey revealed that West African lions now only exist in five West African nations: Senegal, Nigeria and a single trans-frontier population on the shared borders of Benin, Niger and Burkina Faso.

West African lions are genetically distinct from the more well-recognized lions of East and southern Africa. The West African lion is closely related to the now-extinct Barbary lion, which once roamed North Africa. The group also has genetic ties to Asiatic lions.

"West African lions have unique genetic sequences not found in any other lions, including in zoos or captivity," said Christine Breitenmoser, the co-chair of the IUCN/SCC Cat Specialist Group, which determines the conservation status of wild cats around the world. "If we lose the lion in West Africa, we will lose a unique, locally adapted population found no-where else. It makes their conservation even more urgent."

The number one threat to lion populations is indiscriminate killing by humans protecting livestock, which typically occurs in the form or preemptive or retaliatory attacks against the cats, according ot the IUCN. Prey-base depletion is another significant threat.

The loss of lions is so rapid that population studies do little to establish meaningful estimates of lion numbers.

"Every survey we do is inaccurate because as soon as you complete it, it is already out of date; the declines are so rapid," said Dereck Joubert, co-founder of National Geographic's Big Cats Initiative. "It is a terribly sad state of affairs when you can very accurately count the lions in an area because there are so few of them. This is critical work that again confirms that we are underestimating the rate of decline of lion populations and that the situation requires a global emergency intervention."

According to Panthera, the lion's present range in West Africa is less than 50,000km2, an area less than half the size of New York State, and just 1 percent of the lion's original historic range in the region.

"Lions have undergone a catastrophic collapse in West Africa. The countries that have managed to retain them are struggling with pervasive poverty and very little funding for conservation," said Panthera president and study co-author Luke Hunter. "To save the lion - and many other critically endangered mammals including unique populations of cheetahs, African wild dogs and elephants - will require a massive commitment of resources from the international community."