Almost 90% of the bears that currently inhabit the Pyrenees are descendants of the male Pyros

The bear population in the Pyrenees reached 76 individuals in 2022 and in 2023 it reached 83 individuals.

Oliver Thansan
Oliver Thansan
02 April 2024 Tuesday 10:31
5 Reads
Almost 90% of the bears that currently inhabit the Pyrenees are descendants of the male Pyros

The bear population in the Pyrenees reached 76 individuals in 2022 and in 2023 it reached 83 individuals. The data seem very positive, especially when compared to the very few native specimens surviving in 1996, when the first release operation of bears from Slovenia was carried out in the Pyrenees.

The numerical balance, however, hides a biological reality that worries experts and may put the future of this recovered population of bears in the Pyrenees at risk. Without counting the deaths caused by humans (remember that the Cachou poisoning is still pending trial), the main risk for the consolidation of a stable and healthy population of bears in the Pyrenees is now the low biological diversity, due to inbreeding, of the current population. A report (Etat des lieux de la population d'ours) prepared by the French association Pays de l'Ours–Adet highlights that the vast majority of specimens of this species (brown bear, Ursus arctos) currently present in the Pyrenees are descended from only three individuals from Slovenia and that, in conclusion, "the demographic evolution of the bear population hides a poor and deteriorating genetic situation."

"We no longer know on what bases we can reasonably base the hope of a favorable future for the bear population of the Pyrenees," concludes this report from Pays de l'Ours-Adet, an update of a first balance sheet prepared in 2020 with very similar conclusions. . This entity for the study and defense of the bear based in Arbas (Haute Garonne, France) has proposed on several occasions the need to improve the biological diversity of the population of this species in the Pyrenees with the incorporation of new male specimens, especially having into account what they consider "essential" to replace individuals killed by human actions, as was the case with the poisoning of the male Cachou, in Les (Aran) in April 2020.

Two data presented in the new report indicate that “almost 90% of the bears present [currently] in the Pyrenees are descendants of the Pyros male, including the current dominant males.” Furthermore, "in 2023, more than 90% of the bears present come from 3 individuals: the females Mellba and Hvala, and the male Pyros," says Pays de l’Ours–Adet.

The genetic data analyzed show that "with the exception of the male Cannellito [Canelito], all bears present come from the 11 bears released since 1996 in the Pyrenees [from Slovenia]." The reproductive life of the specimens transferred to the Pyrenees has been very uneven.

Seven of the 11 released bears bred, but with very different successes:

From the female Ziva (released in 1996) only one offspring remains: Nere, now 27 years old, who has had 5 offspring, none of which have reproduced to date.

Of the second female released in 1996, Mellba, only the female Caramelles remained, who had 20 cubs before being shot by a hunter in 2021.

The Pyros male, released in 1997, remained the dominant male until 2017, when he was reported missing.

The females Palouma, Franska and Sarousse, released in 2006, disappeared without having had a cub.

The female Hvala, also released in 2006, had 11 cubs before disappearing in 2018.

The males Balou and Goiat, released in 2006 and 2016, disappeared in 2014 and 2021. Their offspring (1 and 3 cubs) also disappeared.

The female Sorita, released in 2018, had 7 cubs, 5 of them alive in 2023.

The female Claverina, also released in 2018, is still alive but to date has not given birth to a cub.

The genetic diversity of the population is logically low. A 2020 study presented in the appendix to the 2021 Cross-Border Monitoring Group report stated:

“Almost 70% of the genetic heritage of the population is generated by a single male (Pyros) and a single female (Hvala)”

"The dominant male Pyros alone contributes almost 50% of the population's gene pool, while presenting low individual genetic diversity."

Many litters are inbred: “between 2006 and 2020, there were 13 matings between father and daughter, four between brother and sister, and one mating between a half-brother and half-sister. »

Logically, the indicators of the genetic health of the population are not good:

The effective population (number of individuals that actually contribute to the genetic future of the population) is only 8.2, while a viable population must have at least 50.

The inbreeding coefficient doubled between 2006 and 2020, going from 0.06 to 0.13. The threshold that must not be exceeded is 0.20.

Population heterozygosity is significantly lower in 2020 than in 2006 (from 0.572 to 0.637).

"Therefore, we have generally observed a loss of genetic diversity in the Pyrenean ursine population since 2006."

The 2020 study has not been updated, indicates the French association author of the new report. "We could have had some hope, but everything suggests that the situation has deteriorated even further, considering the events that have occurred since then," says Adet. Among the negative sections, the following stand out:

Disappearance of the male Goiat (released in 2016) and all his descendants;

Disappearance of the only descendant of the male Balou (released in 2006), he himself disappeared;

Disappearance of the female Sarousse (released in 2006), without offspring;

The Nere male, now 27 years old, has not bred since 2020 and none of his offspring have bred yet;

The Cannellito male (the only carrier of the gene in the Pyrenean stock population) has not yet reproduced;

The female Claverina (released in 2018) has not yet bred;

The only surviving cubs of the female Sorita are fathered by a descendant of the ultra-dominant male Pyros.