Almost 2,000 endangered seals have mysteriously been found dead on Russia’s Caspian Sea coast.

Officials in the Russian province of Dagestan initially said that 700 dead Caspian seals had been discovered.

But on Sunday Zaur Gapizov, the director general of the Caspian Environmental Protection Center, said the number had risen to at least 1,700, according to Russian state-owned news agency RIA Novosti.

Gapizov said the seals likely died a couple of weeks ago and there was no evidence that they were killed by poachers.

“Signs of violent death, no remains of fishing nets were found,” Gapizov said.

“Most likely, the number of dead seals is much higher. The coastal patrol of the Caspian Environmental Center, as well as inspectors from the Federal Agency for Fishery and employees of other environmental departments continue to explore the coast.”

Russian authorities said the seals likely died of natural causes, although the reason remained unknown.

Specialists from Russia’s Federal Fisheries Agency and prosecutors inspected the coastline and collected data for research.

Data about the number of seals in the Caspian Sea varies. The fisheries agency puts the number between 270,000 and 300,000 while the environmental center estimates it is not more than 70,000.

Dead seals are found washed up on Dagestan’s shores of the Caspian Sea every few years.

The latest incident comes after more than 200 Caspian seals were found dead on Kazakhstani coast of the Caspian Sea this year, according to KASPIKA, an agency for the conservation of Caspian seals.

Caspian seals, the only mammal living in the Caspian Sea, have been listed as endangered by the International Union for Conservation of Nature (IUCN) since 2008.

They live only in the Caspian Sea, the largest landlocked body of water in the world borders by Russia, Azerbaijan, Kazakhstan, Turkmenistan and Iran.

According to the IUCN, the Caspian seal population declined by more than 70 percent in the 20th century, primarily due to unsustainable hunting for their fur and blubber.

“Currently the main threats for Caspian seals stem from human activities, including very high rates of seal mortality in fishing gear set for sturgeon poaching, and habitat degradation arising from coastal development,” Dr. Simon Goodman, an ecologist at the University of Leeds, said last year.

“Also a concern are reductions in the winter sea ice the seals use for breeding, and a decline in the Caspian Sea level predicted for the coming decades due to climate heating.”

Newsweek has contacted The Caspian Environmental Protection Center and the Federal Fisheries Agency for further comment.