An elderly brown bear in the Pyrenees is facing castration or segregation amid fears that his sexual dominance is threatening the species' survival in the region by limiting genetic diversity.

Pyros, one of the oldest of the 30 or so bears who roam the mountains between France and Spain, is the father, grandfather or great-grandfather of nearly all of the cubs born in the Pyrenees over the past two decades. There are four other males in the colony – only one of them is not related to Pyros – and none of them have fathered any offspring.

Spanish officials said they were being forced to decide between castration or segregation for Pyros after the recent birth of a cub who was both his daughter and grand-daughter.

"If he keeps up this sexual vigour and dominant attitude for a few more years, the other males in the mountains have no chance of mating with any of the females," José Enrique Arró, the councillor who oversees environmental issues in the Val d'Aran, told La Vanguardia.

Officials in Spain and France have been working for more than a decade to reintroduce brown bears to the mountain range. Now the colony's survival is threatened by serious inbreeding, much of it directly linked to the continued sexual dominance of Pyros. Most brown bears are sexual active until they reach 19 years of age. But Pyros, now aged 26, shows no sign of slowing down.

At a recent meeting in France, several strategies were suggested to deal with Pyros's sexual dominance. Arró is pushing for a solution to the problem before a new male bear, probably from Slovenia, is introduced to the area next spring.

Two possibilities were being considered, Ignasi Rodríguez, from the Catalan regional government, told La Vanguardia. "One of them is the capture of Pyros and finding him a new home, perhaps in a sanctuary for bears," he said. The cost of this plan and, more importantly, whether tranquillising and moving Pyros would affect his health or cause possibly fatal stress, have yet to be determined. If he did survive the move, another question is how Pyros would adapt after 26 years of living in the wild.

The other possibility, said Rodríguez, would be to "sterilise him and leave him in the mountains". However, there are concerns that Pyros's dominant behaviour would continue, in effect hindering the chances of other males without offering any kind of viable alternative.

Local officials are hoping that Pyros will be spared either fate by his biological clock. As bears age, they lose their teeth, making it difficult to eat and making them appear less vigorous to females. For most bears this decline begins in their late teens. Now regional officials are keeping their fingers crossed that old age might just be what saves this colony of bears.