There were thousands of dead seals on the Russian coast.
The number of dead seals is still being counted, but the current count is 2,500, according to a Telegram post by the Ministry of Natural Resources.
Many of the seals were found between the mouths of the Shurinka river and the Yuzbash Canal.
The ministry did not say why the seals had died, but said that tests would be conducted to find out.
The head of the Caspian Environmental Protection Center, Zaur Gapizov, told the Associated Press that there was no evidence that the seals were killed by fishing nets.
Over the past decade, there have been a number of dead seals washing up on the shores of Dagestan.
The only marine mammal found in the Caspian Sea is listed as an "Endangered" species.
Fishing nets, hunting, and loss of habitat are threats to the species.