About 2,500 seals have been found dead on the Caspian Sea coast in southern Russia, officials said on Sunday.
Regional officials initially reported on Saturday that 700 dead seals had been found on the coast, but the Russian Ministry of Natural Resources and Environment later raised the figure to about 2,500.
Authorities in the Russian province of Dagestan said it was unclear why the mass deaths happened but that it was likely due to natural causes.
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.
Caspian seals are classified as endangered on the International Union for Conservation of Nature (IUCN) red list.
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 at the Federal Fisheries Agency and prosecutors inspected the coastline and collected data for laboratory research, which didn’t immediately spot any pollutants. Officials are now awaiting laboratory test results.
Several previous incidents of mass seal deaths have been attributed to natural causes. Kazakhstan, which has a long Caspian coastline, reported at least three such incidents this year.