Around 2,200 Caspian Seals -- the only mammals that live in the Caspian Sea -- have washed up dead on the shores of Kazakhstan since November 2024.

Following tests, Kazakhstan's agriculture ministry said "chronic toxicosis, carnivore plague, acute pneumonia, and asphyxiation due to the release of natural gas from the seabed" were to blame.

Chronic toxicosis is an accumulation of pollutants in the seals' bodies which disrupts their immune system.

"The decline in seal numbers is due to a decline in the animals' immunity and their susceptibility to various diseases," the ministry said.

"Unfavourable climatic factors, such as the falling level of the Caspian Sea," as well as shorter winters and global warming were among the main threats facing the endangered species.

Human activities such as "winter shipping and fishing nets" also threatened the seals, Kazakhstan said.

The seal population has plunged by more than 70 percent over the last century, according to the International Union for Conservation of Nature.

Kazakhstan estimates there are now around 270,000 left.

All five nations that surround the Caspian Sea -- Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan -- have periodically reported discovering huge numbers of dead seals on their shores.