Hypoxia is believed to be the most likely cause of the seals' deaths, Svetlana Radionova of Russia's natural resources monitoring agency Rosprirodnadzor told state-run Rossiya 24 television.
Radionova said scientists are investigating whether natural gas emissions in the Caspian Sea could explain the low oxygen levels.
The first results of the examinations are expected by the end of the week, according to the official. The aim is to determine whether water contamination from the large natural gas reserves exploited in the Caspian Sea could have been one of the causes.
Число обнаруженных мертвых краснокнижных нерп на побережье Каспийского моря в Дагестане увеличилось до 2,5 тыс. Подсчет количества погибших животных продолжается, сообщается на официальном Telegram-канале министерства природных ресурсов и экологии региона:https://t.co/Ico9k8QVctpic.twitter.com/MLFtxKVz9Q
The number of dead Red Book seals found on the coast of the Caspian Sea in Dagestan has increased to 2.5 thousand, counting the number of dead animals continues, according to the official Telegram channel of the Ministry of Natural Resources and Environment of the region.
According to Radionova, a similar tragedy occurred in 2000, when a mass die-off of some 2 000 seals was recorded in Dagestan and neighboring Azerbaijan.
The Caspian seal, declared endangered in 2008, is the only mammal living in the Caspian Sea, the world's largest inland body of water stretching between Europe and Asia.