A “highly unusual” number of reindeer deaths has been reported in Norway’s Svalbard region, according to the country’s authorities.

The Governor of Svalbard has found 13 recently deceased reindeer as part of the annual population count, a figure described as “highly unusual” for the summer.

“It is very unusual for breeding-age females and adult males to die during the summer. That’s why we want to monitor this development closely,” the Governor’s office said.

The Norwegian Institute for Nature Research noted that the causes of the deaths are not yet known and that there is “no clear indication or specific hypothesis” to explain them.

“Veterinary specialists are naturally looking for an explanation related to disease. However, it seems unlikely that a disease would primarily affect the most robust animals,” said the Institute’s Senior Research Scientist, Vebjørn Veiberg.