The proportion of polar bear females around the Arctic islands of Svalbard who gave birth to cubs crashed to just 10% in 2014, according to a small scientific survey of the animals. It follows a series of warm years and poor sea ice.

The Barents Sea population of a few thousand polar bears is one of the biggest in the world. But global warming is rapidly reducing the extent of sea ice on which the bears hunt seals, their main food.

The annual survey undertaken by Jon Aars and his colleagues at the Norwegian Polar Institute was conducted in April, just after cubs and mothers leave their dens. They discovered that just three of the 29 adult females they tracked and examined had a cub born that year.

"This is a lower number than we would have expected," he told the Guardian. "Typically one third or more of the adult females have cubs from that year." But even this higher level is in long-term decline: annual records dating back two decades show that about half of adult females in Svalbard had cubs in the mid-1990s.

"Maybe this [year's low number] was because we have had mild years recently with worse ice conditions or maybe it was just a bad year," said Aars, who says it is too early to conclude the population is collapsing. "It is alarming but it is quite a small sample, so we have to be careful. But if this is something that repeats itself in coming years then it will be a concern."

Like a number of polar populations in remote regions, scientists do not have enough data to say whether Barents Sea polar bear numbers are rising or falling. Aars is confident that numbers bounced back after mass killing of polar bears by hunters was outlawed on Svalbard in 1973, and lie somewhere between 1900 and 3600.

"They were nearly hunted to extinction," he said. "But we are pretty sure there are more bears now than in 1973, probably about twice as many."

As to the future, he said: "With worse and worse sea ice conditions we think there will come a point when the population will suffer, but we don't know when that point is."

Winter ice cover in the Arctic fell to its fifth lowest extent on record in 2014. This continues a long-term trend of decline which is occurring more rapidly than scientists expected and the ice cap could vanish in summer within decades.