About 2,500 seals have been found dead on the Caspian Sea coast in southern Russia.
The mass die-off was likely due to ‘natural causes’ rather than fishing or hunting, officials have said.
Caspian seals - the only mammals found in the Caspian sea - are classified as endangered on the International Union for Conservation of Nature (IUCN) red list.
In 1900, there were more than a million of the seals - but after a century of overfishing and habitat degradation, there are just 70,000 left, according to the Caspian Environmental Protection Centre.
Why did 2,500 seals die in Russia?
Regional officials initially reported Saturday that 700 dead seals were found on the coast, but the Dagestan division of the Russian Ministry of Natural Resources and Environment later raised the figure to about 2,500.
Zaur Gapizov, head of the Caspian Environmental Protection Center, said in a statement that the seals likely died a couple of weeks ago. He added that there was no sign that they were killed or caught in fishing nets.
Experts of the Federal Fisheries Agency and prosecutors inspected the coastline and collected data for laboratory research, which didn't immediately spot any pollutants.
Data about the number of seals in the Caspian vary widely. The fisheries agency has said the overall number of Caspian seals is 270,000-300,000, while the Caspian Environmental Protection Center put the number at 70,000.