On Saturday, around 700 dead seals were found, but on Sunday the death toll increased to 2,500. It is the highest death toll in the last ten years, the BBC reports.
- There are no bullet holes here, they haven't trampled each other to death, they haven't drowned either.
The most likely cause is canine distemper virus.
There is a risk that it was environmental toxins, but then not so many seals would die at once, says Tom Arnbom at WWF.
Caspian seals are declining sharply each year by 5 to 8 percent, and there are about 70,000 left, according to the WWF.
- It is quite a large part of the population that has died.
But they can come back if the conditions are right, says Arnbom.
Seals are a large consumer of fish.
Their role in the ecosystem includes regulating fish and removing the dead fish.